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avoid looking at errno for short read_in_full() returns

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When a caller tries to read a particular set of bytes via
read_in_full(), there are three possible outcomes:

  1. An error, in which case -1 is returned and errno is
     set.

  2. A short read, in which fewer bytes are returned and
     errno is unspecified (we never saw a read error, so we
     may have some random value from whatever syscall failed
     last).

  3. The full read completed successfully.

Many callers handle cases 1 and 2 together by just checking
the result against the requested size. If their combined
error path looks at errno (e.g., by calling die_errno), they
may report a nonsense value.

Let's fix these sites by having them distinguish between the
two error cases. That avoids the random errno confusion, and
lets us give more detailed error messages.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King
2017-09-27 02:01:07 -04:00
committed by Junio C Hamano
parent 61d36330b4
commit 90dca6710e
2 changed files with 14 additions and 4 deletions
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7
pack-write.c
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@ -213,14 +213,19 @@ void fixup_pack_header_footer(int pack_fd,
git_SHA_CTX old_sha1_ctx, new_sha1_ctx;
struct pack_header hdr;
char *buf;
ssize_t read_result;
git_SHA1_Init(&old_sha1_ctx);
git_SHA1_Init(&new_sha1_ctx);
if (lseek(pack_fd, 0, SEEK_SET) != 0)
die_errno("Failed seeking to start of '%s'", pack_name);
if (read_in_full(pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
read_result = read_in_full(pack_fd, &hdr, sizeof(hdr));
if (read_result < 0)
die_errno("Unable to reread header of '%s'", pack_name);
else if (read_result != sizeof(hdr))
die_errno("Unexpected short read for header of '%s'",
pack_name);
if (lseek(pack_fd, 0, SEEK_SET) != 0)
die_errno("Failed seeking to start of '%s'", pack_name);
git_SHA1_Update(&old_sha1_ctx, &hdr, sizeof(hdr));