Make pack creation always fsync() the result

This means that we can depend on packs always being stable on disk,
simplifying a lot of the object serialization worries.  And unlike loose
objects, serializing pack creation IO isn't going to be a performance
killer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -515,10 +515,12 @@ static void write_pack_file(void)
 		 * If so, rewrite it like in fast-import
 		 */
 		if (pack_to_stdout || nr_written == nr_remaining) {
-			sha1close(f, sha1, 1);
+			unsigned flags = pack_to_stdout ? CSUM_CLOSE : CSUM_FSYNC;
+			sha1close(f, sha1, flags);
 		} else {
 			int fd = sha1close(f, NULL, 0);
 			fixup_pack_header_footer(fd, sha1, pack_tmp_name, nr_written);
+			fsync_or_die(fd, pack_tmp_name);
 			close(fd);
 		}
 

cache.h

@@ -761,6 +761,7 @@ extern ssize_t 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);
 extern int write_or_whine_pipe(int fd, const void *buf, size_t count, const char *msg);
+extern void fsync_or_die(int fd, const char *);
 
 /* pager.c */
 extern void setup_pager(void);

csum-file.c

@@ -32,21 +32,24 @@ static void sha1flush(struct sha1file *f, unsigned int count)
 	}
 }
 
-int sha1close(struct sha1file *f, unsigned char *result, int final)
+int sha1close(struct sha1file *f, unsigned char *result, unsigned int flags)
 {
 	int fd;
 	unsigned offset = f->offset;
+
 	if (offset) {
 		SHA1_Update(&f->ctx, f->buffer, offset);
 		sha1flush(f, offset);
 		f->offset = 0;
 	}
-	if (final) {
+	if (flags & (CSUM_CLOSE | CSUM_FSYNC)) {
 		/* write checksum and close fd */
 		SHA1_Final(f->buffer, &f->ctx);
 		if (result)
 			hashcpy(result, f->buffer);
 		sha1flush(f, 20);
+		if (flags & CSUM_FSYNC)
+			fsync_or_die(f->fd, f->name);
 		if (close(f->fd))
 			die("%s: sha1 file error on close (%s)",
 			    f->name, strerror(errno));

csum-file.h

@@ -16,9 +16,13 @@ struct sha1file {
 	unsigned char buffer[8192];
 };
 
+/* sha1close flags */
+#define CSUM_CLOSE	1
+#define CSUM_FSYNC	2
+
 extern struct sha1file *sha1fd(int fd, const char *name);
 extern struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp);
-extern int sha1close(struct sha1file *, unsigned char *, int);
+extern int sha1close(struct sha1file *, unsigned char *, unsigned int);
 extern int sha1write(struct sha1file *, void *, unsigned int);
 extern void crc32_begin(struct sha1file *);
 extern uint32_t crc32_end(struct sha1file *);

fast-import.c

@@ -890,7 +890,7 @@ static char *create_index(void)
 		SHA1_Update(&ctx, (*c)->sha1, 20);
 	}
 	sha1write(f, pack_data->sha1, sizeof(pack_data->sha1));
-	sha1close(f, NULL, 1);
+	sha1close(f, NULL, CSUM_FSYNC);
 	free(idx);
 	SHA1_Final(pack_data->sha1, &ctx);
 	return tmpfile;

index-pack.c

@@ -694,6 +694,7 @@ static void final(const char *final_pack_name, const char *curr_pack_name,
 	if (!from_stdin) {
 		close(input_fd);
 	} else {
+		fsync_or_die(output_fd, curr_pack_name);
 		err = close(output_fd);
 		if (err)
 			die("error while closing pack file: %s", strerror(errno));

pack-write.c

@@ -139,7 +139,7 @@ char *write_idx_file(char *index_name, struct pack_idx_entry **objects,
 	}
 
 	sha1write(f, sha1, 20);
-	sha1close(f, NULL, 1);
+	sha1close(f, NULL, CSUM_FSYNC);
 	SHA1_Final(sha1, &ctx);
 	return index_name;
 }

write_or_die.c

@@ -78,6 +78,13 @@ ssize_t write_in_full(int fd, const void *buf, size_t count)
 	return total;
 }
 
+void fsync_or_die(int fd, const char *msg)
+{
+	if (fsync(fd) < 0) {
+		die("%s: fsync error (%s)", msg, strerror(errno));
+	}
+}
+
 void write_or_die(int fd, const void *buf, size_t count)
 {
 	if (write_in_full(fd, buf, count) < 0) {