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Merge branch 'kg/packed-ref-cache-fix'

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Avoid mmapping small files while using packed refs (especially ones
with zero size, which would cause later munmap() to fail).

* kg/packed-ref-cache-fix:
  packed_ref_cache: don't use mmap() for small files
  load_contents(): don't try to mmap an empty file
  packed_ref_iterator_begin(): make optimization more general
  find_reference_location(): make function safe for empty snapshots
  create_snapshot(): use `xmemdupz()` rather than a strbuf
  struct snapshot: store `start` rather than `header_len`
This commit is contained in:
Junio C Hamano 2018-02-15 14:55:42 -08:00
commit 9db22910f7
1 changed files with 55 additions and 51 deletions
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106
refs/packed-backend.c
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@ -68,17 +68,21 @@ struct snapshot {
int mmapped;
/*
* The contents of the `packed-refs` file. If the file was
* already sorted, this points at the mmapped contents of the
* file. If not, this points at heap-allocated memory
* containing the contents, sorted. If there were no contents
* (e.g., because the file didn't exist), `buf` and `eof` are
* both NULL.
* The contents of the `packed-refs` file:
*
* - buf -- a pointer to the start of the memory
* - start -- a pointer to the first byte of actual references
* (i.e., after the header line, if one is present)
* - eof -- a pointer just past the end of the reference
* contents
*
* If the `packed-refs` file was already sorted, `buf` points
* at the mmapped contents of the file. If not, it points at
* heap-allocated memory containing the contents, sorted. If
* there were no contents (e.g., because the file didn't
* exist), `buf`, `start`, and `eof` are all NULL.
*/
char *buf, *eof;
/* The size of the header line, if any; otherwise, 0: */
size_t header_len;
char *buf, *start, *eof;
/*
* What is the peeled state of the `packed-refs` file that
@ -169,8 +173,7 @@ static void clear_snapshot_buffer(struct snapshot *snapshot)
} else {
free(snapshot->buf);
}
snapshot->buf = snapshot->eof = NULL;
snapshot->header_len = 0;
snapshot->buf = snapshot->start = snapshot->eof = NULL;
}
/*
@ -319,13 +322,14 @@ static void sort_snapshot(struct snapshot *snapshot)
size_t len, i;
char *new_buffer, *dst;
pos = snapshot->buf + snapshot->header_len;
pos = snapshot->start;
eof = snapshot->eof;
len = eof - pos;
if (!len)
if (pos == eof)
return;
len = eof - pos;
/*
* Initialize records based on a crude estimate of the number
* of references in the file (we'll grow it below if needed):
@ -391,9 +395,8 @@ static void sort_snapshot(struct snapshot *snapshot)
* place:
*/
clear_snapshot_buffer(snapshot);
snapshot->buf = new_buffer;
snapshot->buf = snapshot->start = new_buffer;
snapshot->eof = new_buffer + len;
snapshot->header_len = 0;
cleanup:
free(records);
@ -442,23 +445,26 @@ static const char *find_end_of_record(const char *p, const char *end)
*/
static void verify_buffer_safe(struct snapshot *snapshot)
{
const char *buf = snapshot->buf + snapshot->header_len;
const char *start = snapshot->start;
const char *eof = snapshot->eof;
const char *last_line;
if (buf == eof)
if (start == eof)
return;
last_line = find_start_of_record(buf, eof - 1);
last_line = find_start_of_record(start, eof - 1);
if (*(eof - 1) != '\n' || eof - last_line < GIT_SHA1_HEXSZ + 2)
die_invalid_line(snapshot->refs->path,
last_line, eof - last_line);
}
#define SMALL_FILE_SIZE (32*1024)
/*
* Depending on `mmap_strategy`, either mmap or read the contents of
* the `packed-refs` file into the snapshot. Return 1 if the file
* existed and was read, or 0 if the file was absent. Die on errors.
* existed and was read, or 0 if the file was absent or empty. Die on
* errors.
*/
static int load_contents(struct snapshot *snapshot)
{
@ -489,24 +495,23 @@ static int load_contents(struct snapshot *snapshot)
die_errno("couldn't stat %s", snapshot->refs->path);
size = xsize_t(st.st_size);
switch (mmap_strategy) {
case MMAP_NONE:
if (!size) {
return 0;
} else if (mmap_strategy == MMAP_NONE || size <= SMALL_FILE_SIZE) {
snapshot->buf = xmalloc(size);
bytes_read = read_in_full(fd, snapshot->buf, size);
if (bytes_read < 0 || bytes_read != size)
die_errno("couldn't read %s", snapshot->refs->path);
snapshot->eof = snapshot->buf + size;
snapshot->mmapped = 0;
break;
case MMAP_TEMPORARY:
case MMAP_OK:
} else {
snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
snapshot->eof = snapshot->buf + size;
snapshot->mmapped = 1;
break;
}
close(fd);
snapshot->start = snapshot->buf;
snapshot->eof = snapshot->buf + size;
return 1;
}
@ -515,9 +520,11 @@ static int load_contents(struct snapshot *snapshot)
* `refname` starts. If `mustexist` is true and the reference doesn't
* exist, then return NULL. If `mustexist` is false and the reference
* doesn't exist, then return the point where that reference would be
* inserted. In the latter mode, `refname` doesn't have to be a proper
* reference name; for example, one could search for "refs/replace/"
* to find the start of any replace references.
* inserted, or `snapshot->eof` (which might be NULL) if it would be
* inserted at the end of the file. In the latter mode, `refname`
* doesn't have to be a proper reference name; for example, one could
* search for "refs/replace/" to find the start of any replace
* references.
*
* The record is sought using a binary search, so `snapshot->buf` must
* be sorted.
@ -539,7 +546,7 @@ static const char *find_reference_location(struct snapshot *snapshot,
* preceding records all have reference names that come
* *before* `refname`.
*/
const char *lo = snapshot->buf + snapshot->header_len;
const char *lo = snapshot->start;
/*
* A pointer to a the first character of a record whose
@ -547,7 +554,7 @@ static const char *find_reference_location(struct snapshot *snapshot,
*/
const char *hi = snapshot->eof;
while (lo < hi) {
while (lo != hi) {
const char *mid, *rec;
int cmp;
@ -616,9 +623,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
/* If the file has a header line, process it: */
if (snapshot->buf < snapshot->eof && *snapshot->buf == '#') {
struct strbuf tmp = STRBUF_INIT;
char *p;
const char *eol;
char *tmp, *p, *eol;
struct string_list traits = STRING_LIST_INIT_NODUP;
eol = memchr(snapshot->buf, '\n',
@ -628,9 +633,9 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
snapshot->buf,
snapshot->eof - snapshot->buf);
strbuf_add(&tmp, snapshot->buf, eol - snapshot->buf);
tmp = xmemdupz(snapshot->buf, eol - snapshot->buf);
if (!skip_prefix(tmp.buf, "# pack-refs with:", (const char **)&p))
if (!skip_prefix(tmp, "# pack-refs with:", (const char **)&p))
die_invalid_line(refs->path,
snapshot->buf,
snapshot->eof - snapshot->buf);
@ -647,10 +652,10 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
/* perhaps other traits later as well */
/* The "+ 1" is for the LF character. */
snapshot->header_len = eol + 1 - snapshot->buf;
snapshot->start = eol + 1;
string_list_clear(&traits, 0);
strbuf_release(&tmp);
free(tmp);
}
verify_buffer_safe(snapshot);
@ -671,13 +676,12 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
* We don't want to leave the file mmapped, so we are
* forced to make a copy now:
*/
size_t size = snapshot->eof -
(snapshot->buf + snapshot->header_len);
size_t size = snapshot->eof - snapshot->start;
char *buf_copy = xmalloc(size);
memcpy(buf_copy, snapshot->buf + snapshot->header_len, size);
memcpy(buf_copy, snapshot->start, size);
clear_snapshot_buffer(snapshot);
snapshot->buf = buf_copy;
snapshot->buf = snapshot->start = buf_copy;
snapshot->eof = buf_copy + size;
}
@ -924,7 +928,12 @@ static struct ref_iterator *packed_ref_iterator_begin(
*/
snapshot = get_snapshot(refs);
if (!snapshot->buf)
if (prefix && *prefix)
start = find_reference_location(snapshot, prefix, 0);
else
start = snapshot->start;
if (start == snapshot->eof)
return empty_ref_iterator_begin();
iter = xcalloc(1, sizeof(*iter));
@ -934,11 +943,6 @@ static struct ref_iterator *packed_ref_iterator_begin(
iter->snapshot = snapshot;
acquire_snapshot(snapshot);
if (prefix && *prefix)
start = find_reference_location(snapshot, prefix, 0);
else
start = snapshot->buf + snapshot->header_len;
iter->pos = start;
iter->eof = snapshot->eof;
strbuf_init(&iter->refname_buf, 0);