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load_contents(): don't try to mmap an empty file

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We don't actually create zero-length `packed-refs` files, but they are
valid and we should handle them correctly. The old code `xmmap()`ed
such files, which led to an error when `munmap()` was called. So, if
the `packed-refs` file is empty, leave the snapshot at its zero values
and return 0 without trying to read or mmap the file.

Returning 0 also makes `create_snapshot()` exit early, which avoids
the technically undefined comparison `NULL < NULL`.

Reported-by: Kim Gybels <kgybels@infogroep.be>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Michael Haggerty 2018-01-24 12:14:15 +01:00 committed by Junio C Hamano
parent f34242975f
commit 01caf20d57
1 changed files with 6 additions and 7 deletions
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13
refs/packed-backend.c
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@ -461,7 +461,8 @@ static void verify_buffer_safe(struct snapshot *snapshot)
/*
* 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)
{
@ -492,19 +493,17 @@ 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) {
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->mmapped = 0;
break;
case MMAP_TEMPORARY:
case MMAP_OK:
} else {
snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
snapshot->mmapped = 1;
break;
}
close(fd);