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Merge branch 'mh/tempfile' 

The "lockfile" API has been rebuilt on top of a new "tempfile" API.

* mh/tempfile:
  credential-cache--daemon: use tempfile module
  credential-cache--daemon: delete socket from main()
  gc: use tempfile module to handle gc.pid file
  lock_repo_for_gc(): compute the path to "gc.pid" only once
  diff: use tempfile module
  setup_temporary_shallow(): use tempfile module
  write_shared_index(): use tempfile module
  register_tempfile(): new function to handle an existing temporary file
  tempfile: add several functions for creating temporary files
  prepare_tempfile_object(): new function, extracted from create_tempfile()
  tempfile: a new module for handling temporary files
  commit_lock_file(): use get_locked_file_path()
  lockfile: add accessor get_lock_file_path()
  lockfile: add accessors get_lock_file_fd() and get_lock_file_fp()
  create_bundle(): duplicate file descriptor to avoid closing it twice
  lockfile: move documentation to lockfile.h and lockfile.c
This commit is contained in:
Junio C Hamano 2015-08-25 14:57:09 -07:00
parent 424f89f098 9e9033166b
commit db86e61cbb
18 changed files with 964 additions and 625 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

220
Documentation/technical/api-lockfile.txt
View File

@ -1,220 +0,0 @@
lockfile API
============
The lockfile API serves two purposes:
* Mutual exclusion and atomic file updates. When we want to change a
file, we create a lockfile `<filename>.lock`, write the new file
contents into it, and then rename the lockfile to its final
destination `<filename>`. We create the `<filename>.lock` file with
`O_CREAT|O_EXCL` so that we can notice and fail if somebody else has
already locked the file, then atomically rename the lockfile to its
final destination to commit the changes and unlock the file.
* Automatic cruft removal. If the program exits after we lock a file
but before the changes have been committed, we want to make sure
that we remove the lockfile. This is done by remembering the
lockfiles we have created in a linked list and setting up an
`atexit(3)` handler and a signal handler that clean up the
lockfiles. This mechanism ensures that outstanding lockfiles are
cleaned up if the program exits (including when `die()` is called)
or if the program dies on a signal.
Please note that lockfiles only block other writers. Readers do not
block, but they are guaranteed to see either the old contents of the
file or the new contents of the file (assuming that the filesystem
implements `rename(2)` atomically).
Calling sequence
----------------
The caller:
* Allocates a `struct lock_file` either as a static variable or on the
heap, initialized to zeros. Once you use the structure to call the
`hold_lock_file_*` family of functions, it belongs to the lockfile
subsystem and its storage must remain valid throughout the life of
the program (i.e. you cannot use an on-stack variable to hold this
structure).
* Attempts to create a lockfile by passing that variable and the path
of the final destination (e.g. `$GIT_DIR/index`) to
`hold_lock_file_for_update` or `hold_lock_file_for_append`.
* Writes new content for the destination file by either:
* writing to the file descriptor returned by the `hold_lock_file_*`
functions (also available via `lock->fd`).
* calling `fdopen_lock_file` to get a `FILE` pointer for the open
file and writing to the file using stdio.
When finished writing, the caller can:
* Close the file descriptor and rename the lockfile to its final
destination by calling `commit_lock_file` or `commit_lock_file_to`.
* Close the file descriptor and remove the lockfile by calling
`rollback_lock_file`.
* Close the file descriptor without removing or renaming the lockfile
by calling `close_lock_file`, and later call `commit_lock_file`,
`commit_lock_file_to`, `rollback_lock_file`, or `reopen_lock_file`.
Even after the lockfile is committed or rolled back, the `lock_file`
object must not be freed or altered by the caller. However, it may be
reused; just pass it to another call of `hold_lock_file_for_update` or
`hold_lock_file_for_append`.
If the program exits before you have called one of `commit_lock_file`,
`commit_lock_file_to`, `rollback_lock_file`, or `close_lock_file`, an
`atexit(3)` handler will close and remove the lockfile, rolling back
any uncommitted changes.
If you need to close the file descriptor you obtained from a
`hold_lock_file_*` function yourself, do so by calling
`close_lock_file`. You should never call `close(2)` or `fclose(3)`
yourself! Otherwise the `struct lock_file` structure would still think
that the file descriptor needs to be closed, and a commit or rollback
would result in duplicate calls to `close(2)`. Worse yet, if you close
and then later open another file descriptor for a completely different
purpose, then a commit or rollback might close that unrelated file
descriptor.
Error handling
--------------
The `hold_lock_file_*` functions return a file descriptor on success
or -1 on failure (unless `LOCK_DIE_ON_ERROR` is used; see below). On
errors, `errno` describes the reason for failure. Errors can be
reported by passing `errno` to one of the following helper functions:
unable_to_lock_message::
Append an appropriate error message to a `strbuf`.
unable_to_lock_error::
Emit an appropriate error message using `error()`.
unable_to_lock_die::
Emit an appropriate error message and `die()`.
Similarly, `commit_lock_file`, `commit_lock_file_to`, and
`close_lock_file` return 0 on success. On failure they set `errno`
appropriately, do their best to roll back the lockfile, and return -1.
Flags
-----
The following flags can be passed to `hold_lock_file_for_update` or
`hold_lock_file_for_append`:
LOCK_NO_DEREF::
Usually symbolic links in the destination path are resolved
and the lockfile is created by adding ".lock" to the resolved
path. If `LOCK_NO_DEREF` is set, then the lockfile is created
by adding ".lock" to the path argument itself. This option is
used, for example, when locking a symbolic reference, which
for backwards-compatibility reasons can be a symbolic link
containing the name of the referred-to-reference.
LOCK_DIE_ON_ERROR::
If a lock is already taken for the file, `die()` with an error
message. If this option is not specified, trying to lock a
file that is already locked returns -1 to the caller.
The functions
-------------
hold_lock_file_for_update::
Take a pointer to `struct lock_file`, the path of the file to
be locked (e.g. `$GIT_DIR/index`) and a flags argument (see
above). Attempt to create a lockfile for the destination and
return the file descriptor for writing to the file.
hold_lock_file_for_append::
Like `hold_lock_file_for_update`, but before returning copy
the existing contents of the file (if any) to the lockfile and
position its write pointer at the end of the file.
fdopen_lock_file::
Associate a stdio stream with the lockfile. Return NULL
(*without* rolling back the lockfile) on error. The stream is
closed automatically when `close_lock_file` is called or when
the file is committed or rolled back.
get_locked_file_path::
Return the path of the file that is locked by the specified
lock_file object. The caller must free the memory.
commit_lock_file::
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`, close the file descriptor, and
rename the lockfile to its final destination. Return 0 upon
success. On failure, roll back the lock file and return -1,
with `errno` set to the value from the failing call to
`close(2)` or `rename(2)`. It is a bug to call
`commit_lock_file` for a `lock_file` object that is not
currently locked.
commit_lock_file_to::
Like `commit_lock_file()`, except that it takes an explicit
`path` argument to which the lockfile should be renamed. The
`path` must be on the same filesystem as the lock file.
rollback_lock_file::
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`, close the file descriptor and
remove the lockfile. It is a NOOP to call
`rollback_lock_file()` for a `lock_file` object that has
already been committed or rolled back.
close_lock_file::
Take a pointer to the `struct lock_file` initialized with an
earlier call to `hold_lock_file_for_update` or
`hold_lock_file_for_append`. Close the file descriptor (and
the file pointer if it has been opened using
`fdopen_lock_file`). Return 0 upon success. On failure to
`close(2)`, return a negative value and roll back the lock
file. Usually `commit_lock_file`, `commit_lock_file_to`, or
`rollback_lock_file` should eventually be called if
`close_lock_file` succeeds.
reopen_lock_file::
Re-open a lockfile that has been closed (using
`close_lock_file`) but not yet committed or rolled back. This
can be used to implement a sequence of operations like the
following:
* Lock file.
* Write new contents to lockfile, then `close_lock_file` to
cause the contents to be written to disk.
* Pass the name of the lockfile to another program to allow it
(and nobody else) to inspect the contents you wrote, while
still holding the lock yourself.
* `reopen_lock_file` to reopen the lockfile. Make further
updates to the contents.
* `commit_lock_file` to make the final version permanent.

1
Makefile
View File

@ -786,6 +786,7 @@ LIB_OBJS += string-list.o
LIB_OBJS += submodule.o
LIB_OBJS += symlinks.o
LIB_OBJS += tag.o
LIB_OBJS += tempfile.o
LIB_OBJS += trace.o
LIB_OBJS += trailer.o
LIB_OBJS += transport.o

1
builtin/am.c
View File

@ -10,6 +10,7 @@
#include "dir.h"
#include "run-command.h"
#include "quote.h"
#include "tempfile.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "refs.h"

15
builtin/commit.c
View File

@ -324,6 +324,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
struct string_list partial;
struct pathspec pathspec;
int refresh_flags = REFRESH_QUIET;
const char *ret;
if (is_status)
refresh_flags |= REFRESH_UNMERGED;
@ -344,7 +345,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
die(_("unable to create temporary index"));
old_index_env = getenv(INDEX_ENVIRONMENT);
setenv(INDEX_ENVIRONMENT, index_lock.filename.buf, 1);
setenv(INDEX_ENVIRONMENT, get_lock_file_path(&index_lock), 1);
if (interactive_add(argc, argv, prefix, patch_interactive) != 0)
die(_("interactive add failed"));
@ -355,7 +356,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
unsetenv(INDEX_ENVIRONMENT);
discard_cache();
read_cache_from(index_lock.filename.buf);
read_cache_from(get_lock_file_path(&index_lock));
if (update_main_cache_tree(WRITE_TREE_SILENT) == 0) {
if (reopen_lock_file(&index_lock) < 0)
die(_("unable to write index file"));
@ -365,7 +366,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
warning(_("Failed to update main cache tree"));
commit_style = COMMIT_NORMAL;
return index_lock.filename.buf;
return get_lock_file_path(&index_lock);
}
/*
@ -388,7 +389,7 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
if (write_locked_index(&the_index, &index_lock, CLOSE_LOCK))
die(_("unable to write new_index file"));
commit_style = COMMIT_NORMAL;
return index_lock.filename.buf;
return get_lock_file_path(&index_lock);
}
/*
@ -475,9 +476,9 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
die(_("unable to write temporary index file"));
discard_cache();
read_cache_from(false_lock.filename.buf);
return false_lock.filename.buf;
ret = get_lock_file_path(&false_lock);
read_cache_from(ret);
return ret;
}
static int run_status(FILE *fp, const char *index_file, const char *prefix, int nowarn,

32
builtin/gc.c
View File

@ -11,6 +11,7 @@
*/
#include "builtin.h"
#include "tempfile.h"
#include "lockfile.h"
#include "parse-options.h"
#include "run-command.h"
@ -42,20 +43,7 @@ static struct argv_array prune = ARGV_ARRAY_INIT;
static struct argv_array prune_worktrees = ARGV_ARRAY_INIT;
static struct argv_array rerere = ARGV_ARRAY_INIT;
static char *pidfile;
static void remove_pidfile(void)
{
if (pidfile)
unlink(pidfile);
}
static void remove_pidfile_on_signal(int signo)
{
remove_pidfile();
sigchain_pop(signo);
raise(signo);
}
static struct tempfile pidfile;
static void git_config_date_string(const char *key, const char **output)
{
@ -199,20 +187,22 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
uintmax_t pid;
FILE *fp;
int fd;
char *pidfile_path;
if (pidfile)
if (is_tempfile_active(&pidfile))
/* already locked */
return NULL;
if (gethostname(my_host, sizeof(my_host)))
strcpy(my_host, "unknown");
fd = hold_lock_file_for_update(&lock, git_path("gc.pid"),
pidfile_path = git_pathdup("gc.pid");
fd = hold_lock_file_for_update(&lock, pidfile_path,
LOCK_DIE_ON_ERROR);
if (!force) {
static char locking_host[128];
int should_exit;
fp = fopen(git_path("gc.pid"), "r");
fp = fopen(pidfile_path, "r");
memset(locking_host, 0, sizeof(locking_host));
should_exit =
fp != NULL &&
@ -236,6 +226,7 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
if (fd >= 0)
rollback_lock_file(&lock);
*ret_pid = pid;
free(pidfile_path);
return locking_host;
}
}
@ -245,11 +236,8 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
write_in_full(fd, sb.buf, sb.len);
strbuf_release(&sb);
commit_lock_file(&lock);
pidfile = git_pathdup("gc.pid");
sigchain_push_common(remove_pidfile_on_signal);
atexit(remove_pidfile);
register_tempfile(&pidfile, pidfile_path);
free(pidfile_path);
return NULL;
}

1
builtin/pull.c
View File

@ -15,6 +15,7 @@
#include "dir.h"
#include "refs.h"
#include "revision.h"
#include "tempfile.h"
#include "lockfile.h"
enum rebase_type {

26
bundle.c
View File

@ -235,7 +235,9 @@ static int is_tag_in_date_range(struct object *tag, struct rev_info *revs)
return result;
}
static int write_pack_data(int bundle_fd, struct lock_file *lock, struct rev_info *revs)
/* Write the pack data to bundle_fd, then close it if it is > 1. */
static int write_pack_data(int bundle_fd, struct rev_info *revs)
{
struct child_process pack_objects = CHILD_PROCESS_INIT;
int i;
@ -250,13 +252,6 @@ static int write_pack_data(int bundle_fd, struct lock_file *lock, struct rev_inf
if (start_command(&pack_objects))
return error(_("Could not spawn pack-objects"));
/*
* start_command closed bundle_fd if it was > 1
* so set the lock fd to -1 so commit_lock_file()
* won't fail trying to close it.
*/
lock->fd = -1;
for (i = 0; i < revs->pending.nr; i++) {
struct object *object = revs->pending.objects[i].item;
if (object->flags & UNINTERESTING)
@ -416,10 +411,21 @@ int create_bundle(struct bundle_header *header, const char *path,
bundle_to_stdout = !strcmp(path, "-");
if (bundle_to_stdout)
bundle_fd = 1;
else
else {
bundle_fd = hold_lock_file_for_update(&lock, path,
LOCK_DIE_ON_ERROR);
/*
* write_pack_data() will close the fd passed to it,
* but commit_lock_file() will also try to close the
* lockfile's fd. So make a copy of the file
* descriptor to avoid trying to close it twice.
*/
bundle_fd = dup(bundle_fd);
if (bundle_fd < 0)
die_errno("unable to dup file descriptor");
}
/* write signature */
write_or_die(bundle_fd, bundle_signature, strlen(bundle_signature));
@ -445,7 +451,7 @@ int create_bundle(struct bundle_header *header, const char *path,
return -1;
/* write pack */
if (write_pack_data(bundle_fd, &lock, &revs))
if (write_pack_data(bundle_fd, &revs))
return -1;
if (!bundle_to_stdout) {

14
config.c
View File

@ -2066,9 +2066,9 @@ int git_config_set_multivar_in_file(const char *config_filename,
}
close(in_fd);
if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
if (chmod(get_lock_file_path(lock), st.st_mode & 07777) < 0) {
error("chmod on %s failed: %s",
lock->filename.buf, strerror(errno));
get_lock_file_path(lock), strerror(errno));
ret = CONFIG_NO_WRITE;
goto out_free;
}
@ -2151,7 +2151,7 @@ int git_config_set_multivar_in_file(const char *config_filename,
return ret;
write_err_out:
ret = write_error(lock->filename.buf);
ret = write_error(get_lock_file_path(lock));
goto out_free;
}
@ -2252,9 +2252,9 @@ int git_config_rename_section_in_file(const char *config_filename,
fstat(fileno(config_file), &st);
if (chmod(lock->filename.buf, st.st_mode & 07777) < 0) {
if (chmod(get_lock_file_path(lock), st.st_mode & 07777) < 0) {
ret = error("chmod on %s failed: %s",
lock->filename.buf, strerror(errno));
get_lock_file_path(lock), strerror(errno));
goto out;
}
@ -2275,7 +2275,7 @@ int git_config_rename_section_in_file(const char *config_filename,
}
store.baselen = strlen(new_name);
if (!store_write_section(out_fd, new_name)) {
ret = write_error(lock->filename.buf);
ret = write_error(get_lock_file_path(lock));
goto out;
}
/*
@ -2301,7 +2301,7 @@ int git_config_rename_section_in_file(const char *config_filename,
continue;
length = strlen(output);
if (write_in_full(out_fd, output, length) != length) {
ret = write_error(lock->filename.buf);
ret = write_error(get_lock_file_path(lock));
goto out;
}
}

25
credential-cache--daemon.c
View File

@ -1,23 +1,11 @@
#include "cache.h"
#include "tempfile.h"
#include "credential.h"
#include "unix-socket.h"
#include "sigchain.h"
#include "parse-options.h"
static const char *socket_path;
static void cleanup_socket(void)
{
if (socket_path)
unlink(socket_path);
}
static void cleanup_socket_on_signal(int sig)
{
cleanup_socket();
sigchain_pop(sig);
raise(sig);
}
static struct tempfile socket_file;
struct credential_cache_entry {
struct credential item;
@ -221,7 +209,6 @@ static void serve_cache(const char *socket_path, int debug)
; /* nothing */
close(fd);
unlink(socket_path);
}
static const char permissions_advice[] =
@ -257,6 +244,7 @@ static void check_socket_directory(const char *path)
int main(int argc, const char **argv)
{
const char *socket_path;
static const char *usage[] = {
"git-credential-cache--daemon [opts] <socket_path>",
NULL
@ -273,12 +261,11 @@ int main(int argc, const char **argv)
if (!socket_path)
usage_with_options(usage, options);
check_socket_directory(socket_path);
atexit(cleanup_socket);
sigchain_push_common(cleanup_socket_on_signal);
register_tempfile(&socket_file, socket_path);
serve_cache(socket_path, debug);
delete_tempfile(&socket_file);
return 0;
}

2
credential-store.c
View File

@ -52,7 +52,7 @@ static void print_entry(struct credential *c)
static void print_line(struct strbuf *buf)
{
strbuf_addch(buf, '\n');
write_or_die(credential_lock.fd, buf->buf, buf->len);
write_or_die(get_lock_file_fd(&credential_lock), buf->buf, buf->len);
}
static void rewrite_credential_file(const char *fn, struct credential *c,

46
diff.c
View File

@ -2,6 +2,7 @@
* Copyright (C) 2005 Junio C Hamano
*/
#include "cache.h"
#include "tempfile.h"
#include "quote.h"
#include "diff.h"
#include "diffcore.h"
@ -308,11 +309,26 @@ static const char *external_diff(void)
return external_diff_cmd;
}
/*
* Keep track of files used for diffing. Sometimes such an entry
* refers to a temporary file, sometimes to an existing file, and
* sometimes to "/dev/null".
*/
static struct diff_tempfile {
const char *name; /* filename external diff should read from */
/*
* filename external diff should read from, or NULL if this
* entry is currently not in use:
*/
const char *name;
char hex[41];
char mode[10];
char tmp_path[PATH_MAX];
/*
* If this diff_tempfile instance refers to a temporary file,
* this tempfile object is used to manage its lifetime.
*/
struct tempfile tempfile;
} diff_temp[2];
typedef unsigned long (*sane_truncate_fn)(char *line, unsigned long len);
@ -597,25 +613,16 @@ static struct diff_tempfile *claim_diff_tempfile(void) {
die("BUG: diff is failing to clean up its tempfiles");
}
static int remove_tempfile_installed;
static void remove_tempfile(void)
{
int i;
for (i = 0; i < ARRAY_SIZE(diff_temp); i++) {
if (diff_temp[i].name == diff_temp[i].tmp_path)
unlink_or_warn(diff_temp[i].name);
if (is_tempfile_active(&diff_temp[i].tempfile))
delete_tempfile(&diff_temp[i].tempfile);
diff_temp[i].name = NULL;
}
}
static void remove_tempfile_on_signal(int signo)
{
remove_tempfile();
sigchain_pop(signo);
raise(signo);
}
static void print_line_count(FILE *file, int count)
{
switch (count) {
@ -2858,8 +2865,7 @@ static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
strbuf_addstr(&template, "XXXXXX_");
strbuf_addstr(&template, base);
fd = git_mkstemps(temp->tmp_path, PATH_MAX, template.buf,
strlen(base) + 1);
fd = mks_tempfile_ts(&temp->tempfile, template.buf, strlen(base) + 1);
if (fd < 0)
die_errno("unable to create temp-file");
if (convert_to_working_tree(path,
@ -2869,8 +2875,8 @@ static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
}
if (write_in_full(fd, blob, size) != size)
die_errno("unable to write temp-file");
close(fd);
temp->name = temp->tmp_path;
close_tempfile(&temp->tempfile);
temp->name = get_tempfile_path(&temp->tempfile);
strcpy(temp->hex, sha1_to_hex(sha1));
temp->hex[40] = 0;
sprintf(temp->mode, "%06o", mode);
@ -2895,12 +2901,6 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
return temp;
}
if (!remove_tempfile_installed) {
atexit(remove_tempfile);
sigchain_push_common(remove_tempfile_on_signal);
remove_tempfile_installed = 1;
}
if (!S_ISGITLINK(one->mode) &&
(!one->sha1_valid ||
reuse_worktree_file(name, one->sha1, 1))) {

211
lockfile.c
View File

@ -1,38 +1,9 @@
/*
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
#include "lockfile.h"
#include "sigchain.h"
static struct lock_file *volatile lock_file_list;
static void remove_lock_files(int skip_fclose)
{
pid_t me = getpid();
while (lock_file_list) {
if (lock_file_list->owner == me) {
/* fclose() is not safe to call in a signal handler */
if (skip_fclose)
lock_file_list->fp = NULL;
rollback_lock_file(lock_file_list);
}
lock_file_list = lock_file_list->next;
}
}
static void remove_lock_files_on_exit(void)
{
remove_lock_files(0);
}
static void remove_lock_files_on_signal(int signo)
{
remove_lock_files(1);
sigchain_pop(signo);
raise(signo);
}
/*
* path = absolute or relative path name
@ -101,60 +72,17 @@ static void resolve_symlink(struct strbuf *path)
/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
size_t pathlen = strlen(path);
int fd;
struct strbuf filename = STRBUF_INIT;
if (!lock_file_list) {
/* One-time initialization */
sigchain_push_common(remove_lock_files_on_signal);
atexit(remove_lock_files_on_exit);
}
strbuf_addstr(&filename, path);
if (!(flags & LOCK_NO_DEREF))
resolve_symlink(&filename);
if (lk->active)
die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
path);
if (!lk->on_list) {
/* Initialize *lk and add it to lock_file_list: */
lk->fd = -1;
lk->fp = NULL;
lk->active = 0;
lk->owner = 0;
strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
lk->next = lock_file_list;
lock_file_list = lk;
lk->on_list = 1;
} else if (lk->filename.len) {
/* This shouldn't happen, but better safe than sorry. */
die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
path);
}
if (flags & LOCK_NO_DEREF) {
strbuf_add_absolute_path(&lk->filename, path);
} else {
struct strbuf resolved_path = STRBUF_INIT;
strbuf_add(&resolved_path, path, pathlen);
resolve_symlink(&resolved_path);
strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
strbuf_release(&resolved_path);
}
strbuf_addstr(&lk->filename, LOCK_SUFFIX);
lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
if (lk->fd < 0) {
strbuf_reset(&lk->filename);
return -1;
}
lk->owner = getpid();
lk->active = 1;
if (adjust_shared_perm(lk->filename.buf)) {
int save_errno = errno;
error("cannot fix permission bits on %s", lk->filename.buf);
rollback_lock_file(lk);
errno = save_errno;
return -1;
}
return lk->fd;
strbuf_addstr(&filename, LOCK_SUFFIX);
fd = create_tempfile(&lk->tempfile, filename.buf);
strbuf_release(&filename);
return fd;
}
/*
@ -287,116 +215,29 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
return fd;
}
FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
{
if (!lk->active)
die("BUG: fdopen_lock_file() called for unlocked object");
if (lk->fp)
die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);
lk->fp = fdopen(lk->fd, mode);
return lk->fp;
}
char *get_locked_file_path(struct lock_file *lk)
{
if (!lk->active)
die("BUG: get_locked_file_path() called for unlocked object");
if (lk->filename.len <= LOCK_SUFFIX_LEN)
struct strbuf ret = STRBUF_INIT;
strbuf_addstr(&ret, get_tempfile_path(&lk->tempfile));
if (ret.len <= LOCK_SUFFIX_LEN ||
strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
die("BUG: get_locked_file_path() called for malformed lock object");
return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
}
int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;
FILE *fp = lk->fp;
int err;
if (fd < 0)
return 0;
lk->fd = -1;
if (fp) {
lk->fp = NULL;
/*
* Note: no short-circuiting here; we want to fclose()
* in any case!
*/
err = ferror(fp) | fclose(fp);
} else {
err = close(fd);
}
if (err) {
int save_errno = errno;
rollback_lock_file(lk);
errno = save_errno;
return -1;
}
return 0;
}
int reopen_lock_file(struct lock_file *lk)
{
if (0 <= lk->fd)
die(_("BUG: reopen a lockfile that is still open"));
if (!lk->active)
die(_("BUG: reopen a lockfile that has been committed"));
lk->fd = open(lk->filename.buf, O_WRONLY);
return lk->fd;
}
int commit_lock_file_to(struct lock_file *lk, const char *path)
{
if (!lk->active)
die("BUG: attempt to commit unlocked object to \"%s\"", path);
if (close_lock_file(lk))
return -1;
if (rename(lk->filename.buf, path)) {
int save_errno = errno;
rollback_lock_file(lk);
errno = save_errno;
return -1;
}
lk->active = 0;
strbuf_reset(&lk->filename);
return 0;
/* remove ".lock": */
strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN);
return strbuf_detach(&ret, NULL);
}
int commit_lock_file(struct lock_file *lk)
{
static struct strbuf result_file = STRBUF_INIT;
int err;
char *result_path = get_locked_file_path(lk);
if (!lk->active)
die("BUG: attempt to commit unlocked object");
if (lk->filename.len <= LOCK_SUFFIX_LEN ||
strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
die("BUG: lockfile filename corrupt");
/* remove ".lock": */
strbuf_add(&result_file, lk->filename.buf,
lk->filename.len - LOCK_SUFFIX_LEN);
err = commit_lock_file_to(lk, result_file.buf);
strbuf_reset(&result_file);
return err;
}
void rollback_lock_file(struct lock_file *lk)
{
if (!lk->active)
return;
if (!close_lock_file(lk)) {
unlink_or_warn(lk->filename.buf);
lk->active = 0;
strbuf_reset(&lk->filename);
if (commit_lock_file_to(lk, result_path)) {
int save_errno = errno;
free(result_path);
errno = save_errno;
return -1;
}
free(result_path);
return 0;
}

320
lockfile.h
View File

@ -4,80 +4,162 @@
/*
* File write-locks as used by Git.
*
* For an overview of how to use the lockfile API, please see
* The lockfile API serves two purposes:
*
* Documentation/technical/api-lockfile.txt
* * Mutual exclusion and atomic file updates. When we want to change
* a file, we create a lockfile `<filename>.lock`, write the new
* file contents into it, and then rename the lockfile to its final
* destination `<filename>`. We create the `<filename>.lock` file
* with `O_CREAT|O_EXCL` so that we can notice and fail if somebody
* else has already locked the file, then atomically rename the
* lockfile to its final destination to commit the changes and
* unlock the file.
*
* This module keeps track of all locked files in lock_file_list for
* use at cleanup. This list and the lock_file objects that comprise
* it must be kept in self-consistent states at all time, because the
* program can be interrupted any time by a signal, in which case the
* signal handler will walk through the list attempting to clean up
* any open lock files.
* * Automatic cruft removal. If the program exits after we lock a
* file but before the changes have been committed, we want to make
* sure that we remove the lockfile. This is done by remembering the
* lockfiles we have created in a linked list and setting up an
* `atexit(3)` handler and a signal handler that clean up the
* lockfiles. This mechanism ensures that outstanding lockfiles are
* cleaned up if the program exits (including when `die()` is
* called) or if the program is terminated by a signal.
*
* A lockfile is owned by the process that created it. The lock_file
* object has an "owner" field that records its owner. This field is
* used to prevent a forked process from closing a lockfile created by
* its parent.
* Please note that lockfiles only block other writers. Readers do not
* block, but they are guaranteed to see either the old contents of
* the file or the new contents of the file (assuming that the
* filesystem implements `rename(2)` atomically).
*
* The possible states of a lock_file object are as follows:
* Most of the heavy lifting is done by the tempfile module (see
* "tempfile.h").
*
* - Uninitialized. In this state the object's on_list field must be
* zero but the rest of its contents need not be initialized. As
* soon as the object is used in any way, it is irrevocably
* registered in the lock_file_list, and on_list is set.
* Calling sequence
* ----------------
*
* - Locked, lockfile open (after hold_lock_file_for_update(),
* hold_lock_file_for_append(), or reopen_lock_file()). In this
* state:
* - the lockfile exists
* - active is set
* - filename holds the filename of the lockfile
* - fd holds a file descriptor open for writing to the lockfile
* - fp holds a pointer to an open FILE object if and only if
* fdopen_lock_file() has been called on the object
* - owner holds the PID of the process that locked the file
* The caller:
*
* - Locked, lockfile closed (after successful close_lock_file()).
* Same as the previous state, except that the lockfile is closed
* and fd is -1.
* * Allocates a `struct lock_file` either as a static variable or on
* the heap, initialized to zeros. Once you use the structure to
* call the `hold_lock_file_for_*()` family of functions, it belongs
* to the lockfile subsystem and its storage must remain valid
* throughout the life of the program (i.e. you cannot use an
* on-stack variable to hold this structure).
*
* - Unlocked (after commit_lock_file(), commit_lock_file_to(),
* rollback_lock_file(), a failed attempt to lock, or a failed
* close_lock_file()). In this state:
* - active is unset
* - filename is empty (usually, though there are transitory
* states in which this condition doesn't hold). Client code should
* *not* rely on the filename being empty in this state.
* - fd is -1
* - the object is left registered in the lock_file_list, and
* on_list is set.
* * Attempts to create a lockfile by calling
* `hold_lock_file_for_update()` or `hold_lock_file_for_append()`.
*
* * Writes new content for the destination file by either:
*
* * writing to the file descriptor returned by the
* `hold_lock_file_for_*()` functions (also available via
* `lock->fd`).
*
* * calling `fdopen_lock_file()` to get a `FILE` pointer for the
* open file and writing to the file using stdio.
*
* When finished writing, the caller can:
*
* * Close the file descriptor and rename the lockfile to its final
* destination by calling `commit_lock_file()` or
* `commit_lock_file_to()`.
*
* * Close the file descriptor and remove the lockfile by calling
* `rollback_lock_file()`.
*
* * Close the file descriptor without removing or renaming the
* lockfile by calling `close_lock_file()`, and later call
* `commit_lock_file()`, `commit_lock_file_to()`,
* `rollback_lock_file()`, or `reopen_lock_file()`.
*
* Even after the lockfile is committed or rolled back, the
* `lock_file` object must not be freed or altered by the caller.
* However, it may be reused; just pass it to another call of
* `hold_lock_file_for_update()` or `hold_lock_file_for_append()`.
*
* If the program exits before `commit_lock_file()`,
* `commit_lock_file_to()`, or `rollback_lock_file()` is called, the
* tempfile module will close and remove the lockfile, thereby rolling
* back any uncommitted changes.
*
* If you need to close the file descriptor you obtained from a
* `hold_lock_file_for_*()` function yourself, do so by calling
* `close_lock_file()`. See "tempfile.h" for more information.
*
*
* Under the covers, a lockfile is just a tempfile with a few helper
* functions. In particular, the state diagram and the cleanup
* machinery are all implemented in the tempfile module.
*
*
* Error handling
* --------------
*
* The `hold_lock_file_for_*()` functions return a file descriptor on
* success or -1 on failure (unless `LOCK_DIE_ON_ERROR` is used; see
* "flags" below). On errors, `errno` describes the reason for
* failure. Errors can be reported by passing `errno` to
* `unable_to_lock_message()` or `unable_to_lock_die()`.
*
* Similarly, `commit_lock_file`, `commit_lock_file_to`, and
* `close_lock_file` return 0 on success. On failure they set `errno`
* appropriately, do their best to roll back the lockfile, and return
* -1.
*/
#include "tempfile.h"
struct lock_file {
struct lock_file *volatile next;
volatile sig_atomic_t active;
volatile int fd;
FILE *volatile fp;
volatile pid_t owner;
char on_list;
struct strbuf filename;
struct tempfile tempfile;
};
/* String appended to a filename to derive the lockfile name: */
#define LOCK_SUFFIX ".lock"
#define LOCK_SUFFIX_LEN 5
/*
* Flags
* -----
*
* The following flags can be passed to `hold_lock_file_for_update()`
* or `hold_lock_file_for_append()`.
*/
/*
* If a lock is already taken for the file, `die()` with an error
* message. If this flag is not specified, trying to lock a file that
* is already locked returns -1 to the caller.
*/
#define LOCK_DIE_ON_ERROR 1
/*
* Usually symbolic links in the destination path are resolved. This
* means that (1) the lockfile is created by adding ".lock" to the
* resolved path, and (2) upon commit, the resolved path is
* overwritten. However, if `LOCK_NO_DEREF` is set, then the lockfile
* is created by adding ".lock" to the path argument itself. This
* option is used, for example, when detaching a symbolic reference,
* which for backwards-compatibility reasons, can be a symbolic link
* containing the name of the referred-to-reference.
*/
#define LOCK_NO_DEREF 2
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
extern NORETURN void unable_to_lock_die(const char *path, int err);
/*
* Attempt to create a lockfile for the file at `path` and return a
* file descriptor for writing to it, or -1 on error. If the file is
* currently locked, retry with quadratic backoff for at least
* timeout_ms milliseconds. If timeout_ms is 0, try exactly once; if
* timeout_ms is -1, retry indefinitely. The flags argument and error
* handling are described above.
*/
extern int hold_lock_file_for_update_timeout(
struct lock_file *lk, const char *path,
int flags, long timeout_ms);
/*
* Attempt to create a lockfile for the file at `path` and return a
* file descriptor for writing to it, or -1 on error. The flags
* argument and error handling are described above.
*/
static inline int hold_lock_file_for_update(
struct lock_file *lk, const char *path,
int flags)
@ -85,15 +167,135 @@ static inline int hold_lock_file_for_update(
return hold_lock_file_for_update_timeout(lk, path, flags, 0);
}
extern int hold_lock_file_for_append(struct lock_file *lk, const char *path,
int flags);
/*
* Like `hold_lock_file_for_update()`, but before returning copy the
* existing contents of the file (if any) to the lockfile and position
* its write pointer at the end of the file. The flags argument and
* error handling are described above.
*/
extern int hold_lock_file_for_append(struct lock_file *lk,
const char *path, int flags);
extern FILE *fdopen_lock_file(struct lock_file *, const char *mode);
extern char *get_locked_file_path(struct lock_file *);
extern int commit_lock_file_to(struct lock_file *, const char *path);
extern int commit_lock_file(struct lock_file *);
extern int reopen_lock_file(struct lock_file *);
extern int close_lock_file(struct lock_file *);
extern void rollback_lock_file(struct lock_file *);
/*
* Append an appropriate error message to `buf` following the failure
* of `hold_lock_file_for_update()` or `hold_lock_file_for_append()`
* to lock `path`. `err` should be the `errno` set by the failing
* call.
*/
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
/*
* Emit an appropriate error message and `die()` following the failure
* of `hold_lock_file_for_update()` or `hold_lock_file_for_append()`
* to lock `path`. `err` should be the `errno` set by the failing
* call.
*/
extern NORETURN void unable_to_lock_die(const char *path, int err);
/*
* Associate a stdio stream with the lockfile (which must still be
* open). Return `NULL` (*without* rolling back the lockfile) on
* error. The stream is closed automatically when `close_lock_file()`
* is called or when the file is committed or rolled back.
*/
static inline FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
{
return fdopen_tempfile(&lk->tempfile, mode);
}
/*
* Return the path of the lockfile. The return value is a pointer to a
* field within the lock_file object and should not be freed.
*/
static inline const char *get_lock_file_path(struct lock_file *lk)
{
return get_tempfile_path(&lk->tempfile);
}
static inline int get_lock_file_fd(struct lock_file *lk)
{
return get_tempfile_fd(&lk->tempfile);
}
static inline FILE *get_lock_file_fp(struct lock_file *lk)
{
return get_tempfile_fp(&lk->tempfile);
}
/*
* Return the path of the file that is locked by the specified
* lock_file object. The caller must free the memory.
*/
extern char *get_locked_file_path(struct lock_file *lk);
/*
* If the lockfile is still open, close it (and the file pointer if it
* has been opened using `fdopen_lock_file()`) without renaming the
* lockfile over the file being locked. Return 0 upon success. On
* failure to `close(2)`, return a negative value and roll back the
* lock file. Usually `commit_lock_file()`, `commit_lock_file_to()`,
* or `rollback_lock_file()` should eventually be called if
* `close_lock_file()` succeeds.
*/
static inline int close_lock_file(struct lock_file *lk)
{
return close_tempfile(&lk->tempfile);
}
/*
* Re-open a lockfile that has been closed using `close_lock_file()`
* but not yet committed or rolled back. This can be used to implement
* a sequence of operations like the following:
*
* * Lock file.
*
* * Write new contents to lockfile, then `close_lock_file()` to
* cause the contents to be written to disk.
*
* * Pass the name of the lockfile to another program to allow it (and
* nobody else) to inspect the contents you wrote, while still
* holding the lock yourself.
*
* * `reopen_lock_file()` to reopen the lockfile. Make further updates
* to the contents.
*
* * `commit_lock_file()` to make the final version permanent.
*/
static inline int reopen_lock_file(struct lock_file *lk)
{
return reopen_tempfile(&lk->tempfile);
}
/*
* Commit the change represented by `lk`: close the file descriptor
* and/or file pointer if they are still open and rename the lockfile
* to its final destination. Return 0 upon success. On failure, roll
* back the lock file and return -1, with `errno` set to the value
* from the failing call to `close(2)` or `rename(2)`. It is a bug to
* call `commit_lock_file()` for a `lock_file` object that is not
* currently locked.
*/
extern int commit_lock_file(struct lock_file *lk);
/*
* Like `commit_lock_file()`, but rename the lockfile to the provided
* `path`. `path` must be on the same filesystem as the lock file.
*/
static inline int commit_lock_file_to(struct lock_file *lk, const char *path)
{
return rename_tempfile(&lk->tempfile, path);
}
/*
* Roll back `lk`: close the file descriptor and/or file pointer and
* remove the lockfile. It is a NOOP to call `rollback_lock_file()`
* for a `lock_file` object that has already been committed or rolled
* back.
*/
static inline void rollback_lock_file(struct lock_file *lk)
{
delete_tempfile(&lk->tempfile);
}
#endif /* LOCKFILE_H */

40
read-cache.c
View File

@ -5,6 +5,7 @@
*/
#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.h"
#include "tempfile.h"
#include "lockfile.h"
#include "cache-tree.h"
#include "refs.h"
@ -2113,7 +2114,7 @@ static int commit_locked_index(struct lock_file *lk)
static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
unsigned flags)
{
int ret = do_write_index(istate, lock->fd, 0);
int ret = do_write_index(istate, get_lock_file_fd(lock), 0);
if (ret)
return ret;
assert((flags & (COMMIT_LOCK | CLOSE_LOCK)) !=
@ -2137,54 +2138,27 @@ static int write_split_index(struct index_state *istate,
return ret;
}
static char *temporary_sharedindex;
static void remove_temporary_sharedindex(void)
{
if (temporary_sharedindex) {
unlink_or_warn(temporary_sharedindex);
free(temporary_sharedindex);
temporary_sharedindex = NULL;
}
}
static void remove_temporary_sharedindex_on_signal(int signo)
{
remove_temporary_sharedindex();
sigchain_pop(signo);
raise(signo);
}
static struct tempfile temporary_sharedindex;
static int write_shared_index(struct index_state *istate,
struct lock_file *lock, unsigned flags)
{
struct split_index *si = istate->split_index;
static int installed_handler;
int fd, ret;
temporary_sharedindex = git_pathdup("sharedindex_XXXXXX");
fd = mkstemp(temporary_sharedindex);
fd = mks_tempfile(&temporary_sharedindex, git_path("sharedindex_XXXXXX"));
if (fd < 0) {
free(temporary_sharedindex);
temporary_sharedindex = NULL;
hashclr(si->base_sha1);
return do_write_locked_index(istate, lock, flags);
}
if (!installed_handler) {
atexit(remove_temporary_sharedindex);
sigchain_push_common(remove_temporary_sharedindex_on_signal);
}
move_cache_to_base_index(istate);
ret = do_write_index(si->base, fd, 1);
close(fd);
if (ret) {
remove_temporary_sharedindex();
delete_tempfile(&temporary_sharedindex);
return ret;
}
ret = rename(temporary_sharedindex,
git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
free(temporary_sharedindex);
temporary_sharedindex = NULL;
ret = rename_tempfile(&temporary_sharedindex,
git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
if (!ret)
hashcpy(si->base_sha1, si->base->sha1);
return ret;

18
refs.c
View File

@ -3401,6 +3401,7 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
{
static char term = '\n';
struct object *o;
int fd;
o = parse_object(sha1);
if (!o) {
@ -3417,11 +3418,12 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
unlock_ref(lock);
return -1;
}
if (write_in_full(lock->lk->fd, sha1_to_hex(sha1), 40) != 40 ||
write_in_full(lock->lk->fd, &term, 1) != 1 ||
fd = get_lock_file_fd(lock->lk);
if (write_in_full(fd, sha1_to_hex(sha1), 40) != 40 ||
write_in_full(fd, &term, 1) != 1 ||
close_ref(lock) < 0) {
strbuf_addf(err,
"Couldn't write %s", lock->lk->filename.buf);
"Couldn't write %s", get_lock_file_path(lock->lk));
unlock_ref(lock);
return -1;
}
@ -4608,7 +4610,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
cb.newlog = fdopen_lock_file(&reflog_lock, "w");
if (!cb.newlog) {
error("cannot fdopen %s (%s)",
reflog_lock.filename.buf, strerror(errno));
get_lock_file_path(&reflog_lock), strerror(errno));
goto failure;
}
}
@ -4633,12 +4635,12 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
status |= error("couldn't write %s: %s", log_file,
strerror(errno));
} else if (update &&
(write_in_full(lock->lk->fd,
(write_in_full(get_lock_file_fd(lock->lk),
sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
write_str_in_full(lock->lk->fd, "\n") != 1 ||
close_ref(lock) < 0)) {
write_str_in_full(get_lock_file_fd(lock->lk), "\n") != 1 ||
close_ref(lock) < 0)) {
status |= error("couldn't write %s",
lock->lk->filename.buf);
get_lock_file_path(lock->lk));
rollback_lock_file(&reflog_lock);
} else if (commit_lock_file(&reflog_lock)) {
status |= error("unable to commit reflog '%s' (%s)",

41
shallow.c
View File

@ -1,4 +1,5 @@
#include "cache.h"
#include "tempfile.h"
#include "lockfile.h"
#include "commit.h"
#include "tag.h"
@ -208,50 +209,28 @@ int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
}
static struct strbuf temporary_shallow = STRBUF_INIT;
static void remove_temporary_shallow(void)
{
if (temporary_shallow.len) {
unlink_or_warn(temporary_shallow.buf);
strbuf_reset(&temporary_shallow);
}
}
static void remove_temporary_shallow_on_signal(int signo)
{
remove_temporary_shallow();
sigchain_pop(signo);
raise(signo);
}
static struct tempfile temporary_shallow;
const char *setup_temporary_shallow(const struct sha1_array *extra)
{
struct strbuf sb = STRBUF_INIT;
int fd;
if (temporary_shallow.len)
die("BUG: attempt to create two temporary shallow files");
if (write_shallow_commits(&sb, 0, extra)) {
strbuf_addstr(&temporary_shallow, git_path("shallow_XXXXXX"));
fd = xmkstemp(temporary_shallow.buf);
atexit(remove_temporary_shallow);
sigchain_push_common(remove_temporary_shallow_on_signal);
fd = xmks_tempfile(&temporary_shallow, git_path("shallow_XXXXXX"));
if (write_in_full(fd, sb.buf, sb.len) != sb.len)
die_errno("failed to write to %s",
temporary_shallow.buf);
close(fd);
get_tempfile_path(&temporary_shallow));
close_tempfile(&temporary_shallow);
strbuf_release(&sb);
return temporary_shallow.buf;
return get_tempfile_path(&temporary_shallow);
}
/*
* is_repository_shallow() sees empty string as "no shallow
* file".
*/
return temporary_shallow.buf;
return get_tempfile_path(&temporary_shallow);
}
void setup_alternate_shallow(struct lock_file *shallow_lock,
@ -267,8 +246,8 @@ void setup_alternate_shallow(struct lock_file *shallow_lock,
if (write_shallow_commits(&sb, 0, extra)) {
if (write_in_full(fd, sb.buf, sb.len) != sb.len)
die_errno("failed to write to %s",
shallow_lock->filename.buf);
*alternate_shallow_file = shallow_lock->filename.buf;
get_lock_file_path(shallow_lock));
*alternate_shallow_file = get_lock_file_path(shallow_lock);
} else
/*
* is_repository_shallow() sees empty string as "no
@ -314,7 +293,7 @@ void prune_shallow(int show_only)
if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
if (write_in_full(fd, sb.buf, sb.len) != sb.len)
die_errno("failed to write to %s",
shallow_lock.filename.buf);
get_lock_file_path(&shallow_lock));
commit_lock_file(&shallow_lock);
} else {
unlink(git_path_shallow());

305
tempfile.c Normal file
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@ -0,0 +1,305 @@
/*
* State diagram and cleanup
* -------------------------
*
* If the program exits while a temporary file is active, we want to
* make sure that we remove it. This is done by remembering the active
* temporary files in a linked list, `tempfile_list`. An `atexit(3)`
* handler and a signal handler are registered, to clean up any active
* temporary files.
*
* Because the signal handler can run at any time, `tempfile_list` and
* the `tempfile` objects that comprise it must be kept in
* self-consistent states at all times.
*
* The possible states of a `tempfile` object are as follows:
*
* - Uninitialized. In this state the object's `on_list` field must be
* zero but the rest of its contents need not be initialized. As
* soon as the object is used in any way, it is irrevocably
* registered in `tempfile_list`, and `on_list` is set.
*
* - Active, file open (after `create_tempfile()` or
* `reopen_tempfile()`). In this state:
*
* - the temporary file exists
* - `active` is set
* - `filename` holds the filename of the temporary file
* - `fd` holds a file descriptor open for writing to it
* - `fp` holds a pointer to an open `FILE` object if and only if
* `fdopen_tempfile()` has been called on the object
* - `owner` holds the PID of the process that created the file
*
* - Active, file closed (after successful `close_tempfile()`). Same
* as the previous state, except that the temporary file is closed,
* `fd` is -1, and `fp` is `NULL`.
*
* - Inactive (after `delete_tempfile()`, `rename_tempfile()`, a
* failed attempt to create a temporary file, or a failed
* `close_tempfile()`). In this state:
*
* - `active` is unset
* - `filename` is empty (usually, though there are transitory
* states in which this condition doesn't hold). Client code should
* *not* rely on the filename being empty in this state.
* - `fd` is -1 and `fp` is `NULL`
* - the object is left registered in the `tempfile_list`, and
* `on_list` is set.
*
* A temporary file is owned by the process that created it. The
* `tempfile` has an `owner` field that records the owner's PID. This
* field is used to prevent a forked process from deleting a temporary
* file created by its parent.
*/
#include "cache.h"
#include "tempfile.h"
#include "sigchain.h"
static struct tempfile *volatile tempfile_list;
static void remove_tempfiles(int skip_fclose)
{
pid_t me = getpid();
while (tempfile_list) {
if (tempfile_list->owner == me) {
/* fclose() is not safe to call in a signal handler */
if (skip_fclose)
tempfile_list->fp = NULL;
delete_tempfile(tempfile_list);
}
tempfile_list = tempfile_list->next;
}
}
static void remove_tempfiles_on_exit(void)
{
remove_tempfiles(0);
}
static void remove_tempfiles_on_signal(int signo)
{
remove_tempfiles(1);
sigchain_pop(signo);
raise(signo);
}
/*
* Initialize *tempfile if necessary and add it to tempfile_list.
*/
static void prepare_tempfile_object(struct tempfile *tempfile)
{
if (!tempfile_list) {
/* One-time initialization */
sigchain_push_common(remove_tempfiles_on_signal);
atexit(remove_tempfiles_on_exit);
}
if (tempfile->active)
die("BUG: prepare_tempfile_object called for active object");
if (!tempfile->on_list) {
/* Initialize *tempfile and add it to tempfile_list: */
tempfile->fd = -1;
tempfile->fp = NULL;
tempfile->active = 0;
tempfile->owner = 0;
strbuf_init(&tempfile->filename, 0);
tempfile->next = tempfile_list;
tempfile_list = tempfile;
tempfile->on_list = 1;
} else if (tempfile->filename.len) {
/* This shouldn't happen, but better safe than sorry. */
die("BUG: prepare_tempfile_object called for improperly-reset object");
}
}
/* Make sure errno contains a meaningful value on error */
int create_tempfile(struct tempfile *tempfile, const char *path)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, path);
tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
if (adjust_shared_perm(tempfile->filename.buf)) {
int save_errno = errno;
error("cannot fix permission bits on %s", tempfile->filename.buf);
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
return tempfile->fd;
}
void register_tempfile(struct tempfile *tempfile, const char *path)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, path);
tempfile->owner = getpid();
tempfile->active = 1;
}
int mks_tempfile_sm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
return tempfile->fd;
}
int mks_tempfile_tsm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode)
{
const char *tmpdir;
prepare_tempfile_object(tempfile);
tmpdir = getenv("TMPDIR");
if (!tmpdir)
tmpdir = "/tmp";
strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
return tempfile->fd;
}
int xmks_tempfile_m(struct tempfile *tempfile, const char *template, int mode)
{
int fd;
struct strbuf full_template = STRBUF_INIT;
strbuf_add_absolute_path(&full_template, template);
fd = mks_tempfile_m(tempfile, full_template.buf, mode);
if (fd < 0)
die_errno("Unable to create temporary file '%s'",
full_template.buf);
strbuf_release(&full_template);
return fd;
}
FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
{
if (!tempfile->active)
die("BUG: fdopen_tempfile() called for inactive object");
if (tempfile->fp)
die("BUG: fdopen_tempfile() called for open object");
tempfile->fp = fdopen(tempfile->fd, mode);
return tempfile->fp;
}
const char *get_tempfile_path(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_path() called for inactive object");
return tempfile->filename.buf;
}
int get_tempfile_fd(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_fd() called for inactive object");
return tempfile->fd;
}
FILE *get_tempfile_fp(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_fp() called for inactive object");
return tempfile->fp;
}
int close_tempfile(struct tempfile *tempfile)
{
int fd = tempfile->fd;
FILE *fp = tempfile->fp;
int err;
if (fd < 0)
return 0;
tempfile->fd = -1;
if (fp) {
tempfile->fp = NULL;
/*
* Note: no short-circuiting here; we want to fclose()
* in any case!
*/
err = ferror(fp) | fclose(fp);
} else {
err = close(fd);
}
if (err) {
int save_errno = errno;
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
return 0;
}
int reopen_tempfile(struct tempfile *tempfile)
{
if (0 <= tempfile->fd)
die("BUG: reopen_tempfile called for an open object");
if (!tempfile->active)
die("BUG: reopen_tempfile called for an inactive object");
tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
return tempfile->fd;
}
int rename_tempfile(struct tempfile *tempfile, const char *path)
{
if (!tempfile->active)
die("BUG: rename_tempfile called for inactive object");
if (close_tempfile(tempfile))
return -1;
if (rename(tempfile->filename.buf, path)) {
int save_errno = errno;
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
tempfile->active = 0;
strbuf_reset(&tempfile->filename);
return 0;
}
void delete_tempfile(struct tempfile *tempfile)
{
if (!tempfile->active)
return;
if (!close_tempfile(tempfile)) {
unlink_or_warn(tempfile->filename.buf);
tempfile->active = 0;
strbuf_reset(&tempfile->filename);
}
}

271
tempfile.h Normal file
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@ -0,0 +1,271 @@
#ifndef TEMPFILE_H
#define TEMPFILE_H
/*
* Handle temporary files.
*
* The tempfile API allows temporary files to be created, deleted, and
* atomically renamed. Temporary files that are still active when the
* program ends are cleaned up automatically. Lockfiles (see
* "lockfile.h") are built on top of this API.
*
*
* Calling sequence
* ----------------
*
* The caller:
*
* * Allocates a `struct tempfile` either as a static variable or on
* the heap, initialized to zeros. Once you use the structure to
* call `create_tempfile()`, it belongs to the tempfile subsystem
* and its storage must remain valid throughout the life of the
* program (i.e. you cannot use an on-stack variable to hold this
* structure).
*
* * Attempts to create a temporary file by calling
* `create_tempfile()`.
*
* * Writes new content to the file by either:
*
* * writing to the file descriptor returned by `create_tempfile()`
* (also available via `tempfile->fd`).
*
* * calling `fdopen_tempfile()` to get a `FILE` pointer for the
* open file and writing to the file using stdio.
*
* When finished writing, the caller can:
*
* * Close the file descriptor and remove the temporary file by
* calling `delete_tempfile()`.
*
* * Close the temporary file and rename it atomically to a specified
* filename by calling `rename_tempfile()`. This relinquishes
* control of the file.
*
* * Close the file descriptor without removing or renaming the
* temporary file by calling `close_tempfile()`, and later call
* `delete_tempfile()` or `rename_tempfile()`.
*
* Even after the temporary file is renamed or deleted, the `tempfile`
* object must not be freed or altered by the caller. However, it may
* be reused; just pass it to another call of `create_tempfile()`.
*
* If the program exits before `rename_tempfile()` or
* `delete_tempfile()` is called, an `atexit(3)` handler will close
* and remove the temporary file.
*
* If you need to close the file descriptor yourself, do so by calling
* `close_tempfile()`. You should never call `close(2)` or `fclose(3)`
* yourself, otherwise the `struct tempfile` structure would still
* think that the file descriptor needs to be closed, and a later
* cleanup would result in duplicate calls to `close(2)`. Worse yet,
* if you close and then later open another file descriptor for a
* completely different purpose, then the unrelated file descriptor
* might get closed.
*
*
* Error handling
* --------------
*
* `create_tempfile()` returns a file descriptor on success or -1 on
* failure. On errors, `errno` describes the reason for failure.
*
* `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile()`
* return 0 on success. On failure they set `errno` appropriately, do
* their best to delete the temporary file, and return -1.
*/
struct tempfile {
struct tempfile *volatile next;
volatile sig_atomic_t active;
volatile int fd;
FILE *volatile fp;
volatile pid_t owner;
char on_list;
struct strbuf filename;
};
/*
* Attempt to create a temporary file at the specified `path`. Return
* a file descriptor for writing to it, or -1 on error. It is an error
* if a file already exists at that path.
*/
extern int create_tempfile(struct tempfile *tempfile, const char *path);
/*
* Register an existing file as a tempfile, meaning that it will be
* deleted when the program exits. The tempfile is considered closed,
* but it can be worked with like any other closed tempfile (for
* example, it can be opened using reopen_tempfile()).
*/
extern void register_tempfile(struct tempfile *tempfile, const char *path);
/*
* mks_tempfile functions
*
* The following functions attempt to create and open temporary files
* with names derived automatically from a template, in the manner of
* mkstemps(), and arrange for them to be deleted if the program ends
* before they are deleted explicitly. There is a whole family of such
* functions, named according to the following pattern:
*
* x?mks_tempfile_t?s?m?()
*
* The optional letters have the following meanings:
*
* x - die if the temporary file cannot be created.
*
* t - create the temporary file under $TMPDIR (as opposed to
* relative to the current directory). When these variants are
* used, template should be the pattern for the filename alone,
* without a path.
*
* s - template includes a suffix that is suffixlen characters long.
*
* m - the temporary file should be created with the specified mode
* (otherwise, the mode is set to 0600).
*
* None of these functions modify template. If the caller wants to
* know the (absolute) path of the file that was created, it can be
* read from tempfile->filename.
*
* On success, the functions return a file descriptor that is open for
* writing the temporary file. On errors, they return -1 and set errno
* appropriately (except for the "x" variants, which die() on errors).
*/
/* See "mks_tempfile functions" above. */
extern int mks_tempfile_sm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode);
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile_s(struct tempfile *tempfile,
const char *template, int suffixlen)
{
return mks_tempfile_sm(tempfile, template, suffixlen, 0600);
}
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile_m(struct tempfile *tempfile,
const char *template, int mode)
{
return mks_tempfile_sm(tempfile, template, 0, mode);
}
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile(struct tempfile *tempfile,
const char *template)
{
return mks_tempfile_sm(tempfile, template, 0, 0600);
}
/* See "mks_tempfile functions" above. */
extern int mks_tempfile_tsm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode);
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile_ts(struct tempfile *tempfile,
const char *template, int suffixlen)
{
return mks_tempfile_tsm(tempfile, template, suffixlen, 0600);
}
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile_tm(struct tempfile *tempfile,
const char *template, int mode)
{
return mks_tempfile_tsm(tempfile, template, 0, mode);
}
/* See "mks_tempfile functions" above. */
static inline int mks_tempfile_t(struct tempfile *tempfile,
const char *template)
{
return mks_tempfile_tsm(tempfile, template, 0, 0600);
}
/* See "mks_tempfile functions" above. */
extern int xmks_tempfile_m(struct tempfile *tempfile,
const char *template, int mode);
/* See "mks_tempfile functions" above. */
static inline int xmks_tempfile(struct tempfile *tempfile,
const char *template)
{
return xmks_tempfile_m(tempfile, template, 0600);
}
/*
* Associate a stdio stream with the temporary file (which must still
* be open). Return `NULL` (*without* deleting the file) on error. The
* stream is closed automatically when `close_tempfile()` is called or
* when the file is deleted or renamed.
*/
extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
static inline int is_tempfile_active(struct tempfile *tempfile)
{
return tempfile->active;
}
/*
* Return the path of the lockfile. The return value is a pointer to a
* field within the lock_file object and should not be freed.
*/
extern const char *get_tempfile_path(struct tempfile *tempfile);
extern int get_tempfile_fd(struct tempfile *tempfile);
extern FILE *get_tempfile_fp(struct tempfile *tempfile);
/*
* If the temporary file is still open, close it (and the file pointer
* too, if it has been opened using `fdopen_tempfile()`) without
* deleting the file. Return 0 upon success. On failure to `close(2)`,
* return a negative value and delete the file. Usually
* `delete_tempfile()` or `rename_tempfile()` should eventually be
* called if `close_tempfile()` succeeds.
*/
extern int close_tempfile(struct tempfile *tempfile);
/*
* Re-open a temporary file that has been closed using
* `close_tempfile()` but not yet deleted or renamed. This can be used
* to implement a sequence of operations like the following:
*
* * Create temporary file.
*
* * Write new contents to file, then `close_tempfile()` to cause the
* contents to be written to disk.
*
* * Pass the name of the temporary file to another program to allow
* it (and nobody else) to inspect or even modify the file's
* contents.
*
* * `reopen_tempfile()` to reopen the temporary file. Make further
* updates to the contents.
*
* * `rename_tempfile()` to move the file to its permanent location.
*/
extern int reopen_tempfile(struct tempfile *tempfile);
/*
* Close the file descriptor and/or file pointer and remove the
* temporary file associated with `tempfile`. It is a NOOP to call
* `delete_tempfile()` for a `tempfile` object that has already been
* deleted or renamed.
*/
extern void delete_tempfile(struct tempfile *tempfile);
/*
* Close the file descriptor and/or file pointer if they are still
* open, and atomically rename the temporary file to `path`. `path`
* must be on the same filesystem as the lock file. Return 0 on
* success. On failure, delete the temporary file and return -1, with
* `errno` set to the value from the failing call to `close(2)` or
* `rename(2)`. It is a bug to call `rename_tempfile()` for a
* `tempfile` object that is not currently active.
*/
extern int rename_tempfile(struct tempfile *tempfile, const char *path);
#endif /* TEMPFILE_H */