Seek back to current filepos when mmap()ing with NO_MMAP

"git-index-pack --fix-thin" relies on mmap() not changing the current
file position (otherwise the pack will be corrupted when writing the
final SHA1). Meet that expectation.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/compat/mmap.c b/compat/mmap.c
index 55cb120..a4d2e50 100644 (file)
--- a/compat/mmap.c
+++ b/compat/mmap.c
@@ -7,6 +7,7 @@
 void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_t offset)
 {
        int n = 0;
+       off_t current_offset = lseek(fd, 0, SEEK_CUR);
 
        if (start != NULL || !(flags & MAP_PRIVATE))
                die("Invalid usage of gitfakemmap.");
@@ -39,6 +40,11 @@ void *gitfakemmap(void *start, size_t length, int prot , int flags, int fd, off_
                n += count;
        }
 
+       if (current_offset != lseek(fd, current_offset, SEEK_SET)) {
+               errno = EINVAL;
+               return MAP_FAILED;
+       }
+
        return start;
 }