Remove read_or_die in favor of better error messages.

Originally I introduced read_or_die for the purpose of reading
the pack header and trailer, and I was too lazy to print proper
error messages.

Linus Torvalds <torvalds@osdl.org>:
> For a read error, at the very least you have to say WHICH FILE
> couldn't be read, because it's usually a matter of some file just
> being too short, not some system-wide problem.

and of course Linus is right. Make it so.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

cache.h

@@ -434,7 +434,6 @@ extern char *git_log_output_encoding;
 
 extern int copy_fd(int ifd, int ofd);
 extern int read_in_full(int fd, void *buf, size_t count);
-extern void read_or_die(int fd, void *buf, size_t count);
 extern int write_in_full(int fd, const void *buf, size_t count);
 extern void write_or_die(int fd, const void *buf, size_t count);
 extern int write_or_whine(int fd, const void *buf, size_t count, const char *msg);

sha1_file.c

@@ -572,7 +572,8 @@ static void open_packed_git(struct packed_git *p)
 		die("cannot set FD_CLOEXEC");
 
 	/* Verify we recognize this pack file format. */
-	read_or_die(p->pack_fd, &hdr, sizeof(hdr));
+	if (read_in_full(p->pack_fd, &hdr, sizeof(hdr)) != sizeof(hdr))
+		die("file %s is far too short to be a packfile", p->pack_name);
 	if (hdr.hdr_signature != htonl(PACK_SIGNATURE))
 		die("file %s is not a GIT packfile", p->pack_name);
 	if (!pack_version_ok(hdr.hdr_version))
@@ -588,7 +589,8 @@ static void open_packed_git(struct packed_git *p)
 			num_packed_objects(p));
 	if (lseek(p->pack_fd, p->pack_size - sizeof(sha1), SEEK_SET) == -1)
 		die("end of packfile %s is unavailable", p->pack_name);
-	read_or_die(p->pack_fd, sha1, sizeof(sha1));
+	if (read_in_full(p->pack_fd, sha1, sizeof(sha1)) != sizeof(sha1))
+		die("packfile %s signature is unavailable", p->pack_name);
 	idx_sha1 = ((unsigned char *)p->index_base) + p->index_size - 40;
 	if (hashcmp(sha1, idx_sha1))
 		die("packfile %s does not match index", p->pack_name);

write_or_die.c

@@ -17,18 +17,6 @@ int read_in_full(int fd, void *buf, size_t count)
 	return total;
 }
 
-void read_or_die(int fd, void *buf, size_t count)
-{
-	ssize_t loaded;
-
-	loaded = read_in_full(fd, buf, count);
-	if (loaded != count) {
-		if (loaded < 0)
-			die("read error (%s)", strerror(errno));
-		die("read error: end of file");
-	}
-}
-
 int write_in_full(int fd, const void *buf, size_t count)
 {
 	const char *p = buf;