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load_contents(): don't try to mmap an empty file
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>
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@ -461,7 +461,8 @@ static void verify_buffer_safe(struct snapshot *snapshot)
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/*
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* Depending on `mmap_strategy`, either mmap or read the contents of
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* the `packed-refs` file into the snapshot. Return 1 if the file
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* existed and was read, or 0 if the file was absent. Die on errors.
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* existed and was read, or 0 if the file was absent or empty. Die on
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* errors.
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*/
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static int load_contents(struct snapshot *snapshot)
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{
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@ -492,19 +493,17 @@ static int load_contents(struct snapshot *snapshot)
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die_errno("couldn't stat %s", snapshot->refs->path);
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size = xsize_t(st.st_size);
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switch (mmap_strategy) {
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case MMAP_NONE:
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if (!size) {
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return 0;
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} else if (mmap_strategy == MMAP_NONE) {
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snapshot->buf = xmalloc(size);
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bytes_read = read_in_full(fd, snapshot->buf, size);
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if (bytes_read < 0 || bytes_read != size)
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die_errno("couldn't read %s", snapshot->refs->path);
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snapshot->mmapped = 0;
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break;
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case MMAP_TEMPORARY:
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case MMAP_OK:
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} else {
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snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
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snapshot->mmapped = 1;
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break;
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}
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close(fd);
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