[PATCH] mmap error handling

I have reviewed all occurrences of mmap() in git and fixed three types
of errors/defects:

1) The result is not checked.
2) The file descriptor is closed if mmap() succeeds, but not when it
fails.
3) Various casts applied to -1 are used instead of MAP_FAILED, which is
specifically defined to check mmap() return value.

[jc: This is a second round of Pavel's patch.  He fixed up the problem
that close() potentially clobbering the errno from mmap, which
the first round had.]

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -377,8 +377,10 @@ int diff_populate_filespec(struct diff_filespec *s, int size_only)
 		if (fd < 0)
 			goto err_empty;
 		s->data = mmap(NULL, s->size, PROT_READ, MAP_PRIVATE, fd, 0);
-		s->should_munmap = 1;
 		close(fd);
+		if (s->data == MAP_FAILED)
+			goto err_empty;
+		s->should_munmap = 1;
 	}
 	else {
 		char type[20];