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wrapper.c: add xpread() similar to xread() 

It is a common mistake to call read(2)/pread(2) and forget to
anticipate that they may return error with EAGAIN/EINTR when the
system call is interrupted.

We have xread() helper to relieve callers of read(2) from having to
worry about it; add xpread() helper to do the same for pread(2).

Update the caller in the builtin/index-pack.c and the mmap emulation
in compat/.

Signed-off-by: Yiannis Marangos <yiannis.marangos@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Yiannis Marangos 2014-04-10 21:54:12 +03:00 committed by Junio C Hamano
parent 7bbc4e8fdb
commit 9aa91af036
4 changed files with 21 additions and 4 deletions
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2
builtin/index-pack.c
View File

@ -542,7 +542,7 @@ static void *unpack_data(struct object_entry *obj,
do {
ssize_t n = (len < 64*1024) ? len : 64*1024;
n = pread(pack_fd, inbuf, n, from);
n = xpread(pack_fd, inbuf, n, from);
if (n < 0)
die_errno(_("cannot pread pack file"));
if (!n)

4
compat/mmap.c
View File

@ -14,7 +14,7 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
}
while (n < length) {
ssize_t count = pread(fd, (char *)start + n, length - n, offset + n);
ssize_t count = xpread(fd, (char *)start + n, length - n, offset + n);
if (count == 0) {
memset((char *)start+n, 0, length-n);
@ -22,8 +22,6 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of
}
if (count < 0) {
if (errno == EAGAIN || errno == EINTR)
continue;
free(start);
errno = EACCES;
return MAP_FAILED;

1
git-compat-util.h
View File

@ -534,6 +534,7 @@ extern void *xcalloc(size_t nmemb, size_t size);
extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
extern ssize_t xread(int fd, void *buf, size_t len);
extern ssize_t xwrite(int fd, const void *buf, size_t len);
extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
extern int xdup(int fd);
extern FILE *xfdopen(int fd, const char *mode);
extern int xmkstemp(char *template);

18
wrapper.c
View File

@ -174,6 +174,24 @@ ssize_t xwrite(int fd, const void *buf, size_t len)
}
}
/*
* xpread() is the same as pread(), but it automatically restarts pread()
* operations with a recoverable error (EAGAIN and EINTR). xpread() DOES
* NOT GUARANTEE that "len" bytes is read even if the data is available.
*/
ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
{
ssize_t nr;
if (len > MAX_IO_SIZE)
len = MAX_IO_SIZE;
while (1) {
nr = pread(fd, buf, len, offset);
if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
continue;
return nr;
}
}
ssize_t read_in_full(int fd, void *buf, size_t count)
{
char *p = buf;