fsck: give accurate error message on empty loose object files

Since 3ba7a065527a (A loose object is not corrupt if it
cannot be read due to EMFILE), "git fsck" on a repository with an empty
loose object file complains with the error message

  fatal: failed to read object <sha1>: Invalid argument

This comes from a failure of mmap on this empty file, which sets errno to
EINVAL. Instead of calling xmmap on empty file, we display a clean error
message ourselves, and return a NULL pointer. The new message is

  error: object file .git/objects/09/<rest-of-sha1> is empty
  fatal: loose object <sha1> (stored in .git/objects/09/<rest-of-sha1>) is corrupt

The second line was already there before the regression in 3ba7a065527a,
and the first is an additional message, that should help diagnosing the
problem for the user.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/sha1_file.c b/sha1_file.c
index 25f6965294fcc6bc440eda32187e0cc2b67e69d1..797b0634cefc1a354b4c6619461e483c64adc9af 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1070,6 +1070,11 @@ static void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 
                if (!fstat(fd, &st)) {
                        *size = xsize_t(st.st_size);
+                       if (!*size) {
+                               /* mmap() is forbidden on empty files */
+                               error("object file %s is empty", sha1_file_name(sha1));
+                               return NULL;
+                       }
                        map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
                }
                close(fd);