diff mbox series

[v2,09/17] midx: return success/failure in chunk write methods

Message ID b3cc73c22567ed89e2537ffaaa04f82a436d9802.1611759716.git.gitgitgadget@gmail.com (mailing list archive)
State Superseded
Headers show
Series Refactor chunk-format into an API | expand

Commit Message

Derrick Stolee Jan. 27, 2021, 3:01 p.m. UTC 
From: Derrick Stolee <dstolee@microsoft.com>

Historically, the chunk-writing methods in midx.c have returned the
amount of data written so the writer method could compare this with the
table of contents. This presents with some interesting issues:

1. If a chunk writing method has a bug that miscalculates the written
   bytes, then we can satisfy the table of contents without actually
   writing the right amount of data to the hashfile. The commit-graph
   writing code checks the hashfile struct directly for a more robust
   verification.

2. There is no way for a chunk writing method to gracefully fail.
   Returning an int presents an opportunity to fail without a die().

3. The current pattern doesn't match chunk_write_fn type exactly, so we
   cannot share code with commit-graph.c

For these reasons, convert the midx chunk writer methods to return an
'int'. Since none of them fail at the moment, they all return 0.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 midx.c | 63 +++++++++++++++++++++++++---------------------------------
 1 file changed, 27 insertions(+), 36 deletions(-)

Comments

Junio C Hamano Feb. 4, 2021, 10:59 p.m. UTC | #1 
"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <dstolee@microsoft.com>
>
> Historically, the chunk-writing methods in midx.c have returned the
> amount of data written so the writer method could compare this with the
> table of contents. This presents with some interesting issues:
>
> 1. If a chunk writing method has a bug that miscalculates the written
>    bytes, then we can satisfy the table of contents without actually
>    writing the right amount of data to the hashfile. The commit-graph
>    writing code checks the hashfile struct directly for a more robust
>    verification.
>
> 2. There is no way for a chunk writing method to gracefully fail.
>    Returning an int presents an opportunity to fail without a die().
>
> 3. The current pattern doesn't match chunk_write_fn type exactly, so we
>    cannot share code with commit-graph.c
>
> For these reasons, convert the midx chunk writer methods to return an
> 'int'. Since none of them fail at the moment, they all return 0.

OK, that makes sense.

In this step I see the same "f->total + f->offset" sprinkled in some
places, but they will all go away in the "midx: use chunk-format API
in write_midx_internal()" step, so it is not such a huge deal.

Thanks.
Derrick Stolee Feb. 5, 2021, 11:42 a.m. UTC | #2 
On 2/4/2021 5:59 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> In this step I see the same "f->total + f->offset" sprinkled in some
> places, but they will all go away in the "midx: use chunk-format API
> in write_midx_internal()" step, so it is not such a huge deal.

I'll move the ones that are introduced by this patch, but others
already exist that also get removed by a later patch. I won't
touch those until they are deleted.

Thanks,
-Stolee
diff mbox series

Patch

diff --git a/midx.c b/midx.c
index 5be081f229a..e23a5fc4903 100644
--- a/midx.c
+++ b/midx.c
@@ -650,7 +650,7 @@  static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 	return deduplicated_entries;
 }
 
-static size_t write_midx_pack_names(struct hashfile *f, void *data)
+static int write_midx_pack_names(struct hashfile *f, void *data)
 {
 	struct write_midx_context *ctx = data;
 	uint32_t i;
@@ -678,14 +678,13 @@  static size_t write_midx_pack_names(struct hashfile *f, void *data)
 	if (i < MIDX_CHUNK_ALIGNMENT) {
 		memset(padding, 0, sizeof(padding));
 		hashwrite(f, padding, i);
-		written += i;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_oid_fanout(struct hashfile *f,
-				    void *data)
+static int write_midx_oid_fanout(struct hashfile *f,
+				 void *data)
 {
 	struct write_midx_context *ctx = data;
 	struct pack_midx_entry *list = ctx->entries;
@@ -710,17 +709,16 @@  static size_t write_midx_oid_fanout(struct hashfile *f,
 		list = next;
 	}
 
-	return MIDX_CHUNK_FANOUT_SIZE;
+	return 0;
 }
 
-static size_t write_midx_oid_lookup(struct hashfile *f,
-				    void *data)
+static int write_midx_oid_lookup(struct hashfile *f,
+				 void *data)
 {
 	struct write_midx_context *ctx = data;
 	unsigned char hash_len = the_hash_algo->rawsz;
 	struct pack_midx_entry *list = ctx->entries;
 	uint32_t i;
-	size_t written = 0;
 
 	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *obj = list++;
@@ -734,19 +732,17 @@  static size_t write_midx_oid_lookup(struct hashfile *f,
 		}
 
 		hashwrite(f, obj->oid.hash, (int)hash_len);
-		written += hash_len;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_object_offsets(struct hashfile *f,
-					void *data)
+static int write_midx_object_offsets(struct hashfile *f,
+				     void *data)
 {
 	struct write_midx_context *ctx = data;
 	struct pack_midx_entry *list = ctx->entries;
 	uint32_t i, nr_large_offset = 0;
-	size_t written = 0;
 
 	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *obj = list++;
@@ -766,20 +762,17 @@  static size_t write_midx_object_offsets(struct hashfile *f,
 			    obj->offset);
 		else
 			hashwrite_be32(f, (uint32_t)obj->offset);
-
-		written += MIDX_CHUNK_OFFSET_WIDTH;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_large_offsets(struct hashfile *f,
-				       void *data)
+static int write_midx_large_offsets(struct hashfile *f,
+				    void *data)
 {
 	struct write_midx_context *ctx = data;
 	struct pack_midx_entry *list = ctx->entries;
 	struct pack_midx_entry *end = ctx->entries + ctx->entries_nr;
-	size_t written = 0;
 	uint32_t nr_large_offset = ctx->num_large_offsets;
 
 	while (nr_large_offset) {
@@ -795,12 +788,12 @@  static size_t write_midx_large_offsets(struct hashfile *f,
 		if (!(offset >> 31))
 			continue;
 
-		written += hashwrite_be64(f, offset);
+		hashwrite_be64(f, offset);
 
 		nr_large_offset--;
 	}
 
-	return written;
+	return 0;
 }
 
 static int write_midx_internal(const char *object_dir, struct multi_pack_index *m,
@@ -812,7 +805,7 @@  static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	struct hashfile *f = NULL;
 	struct lock_file lk;
 	struct write_midx_context ctx = { 0 };
-	uint64_t written = 0;
+	uint64_t header_size = 0;
 	uint32_t chunk_ids[MIDX_MAX_CHUNKS + 1];
 	uint64_t chunk_offsets[MIDX_MAX_CHUNKS + 1];
 	struct progress *progress = NULL;
@@ -940,10 +933,10 @@  static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 		goto cleanup;
 	}
 
-	written = write_midx_header(f, num_chunks, ctx.nr - dropped_packs);
+	header_size = write_midx_header(f, num_chunks, ctx.nr - dropped_packs);
 
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
-	chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
+	chunk_offsets[cur_chunk] = header_size + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
 
 	cur_chunk++;
 	chunk_ids[cur_chunk] = MIDX_CHUNKID_OIDFANOUT;
@@ -981,39 +974,37 @@  static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 		hashwrite_be32(f, chunk_ids[i]);
 		hashwrite_be64(f, chunk_offsets[i]);
-
-		written += MIDX_CHUNKLOOKUP_WIDTH;
 	}
 
 	if (flags & MIDX_PROGRESS)
 		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
 					  num_chunks);
 	for (i = 0; i < num_chunks; i++) {
-		if (written != chunk_offsets[i])
+		if (f->total + f->offset != chunk_offsets[i])
 			BUG("incorrect chunk offset (%"PRIu64" != %"PRIu64") for chunk id %"PRIx32,
 			    chunk_offsets[i],
-			    written,
+			    f->total + f->offset,
 			    chunk_ids[i]);
 
 		switch (chunk_ids[i]) {
 			case MIDX_CHUNKID_PACKNAMES:
-				written += write_midx_pack_names(f, &ctx);
+				write_midx_pack_names(f, &ctx);
 				break;
 
 			case MIDX_CHUNKID_OIDFANOUT:
-				written += write_midx_oid_fanout(f, &ctx);
+				write_midx_oid_fanout(f, &ctx);
 				break;
 
 			case MIDX_CHUNKID_OIDLOOKUP:
-				written += write_midx_oid_lookup(f, &ctx);
+				write_midx_oid_lookup(f, &ctx);
 				break;
 
 			case MIDX_CHUNKID_OBJECTOFFSETS:
-				written += write_midx_object_offsets(f, &ctx);
+				write_midx_object_offsets(f, &ctx);
 				break;
 
 			case MIDX_CHUNKID_LARGEOFFSETS:
-				written += write_midx_large_offsets(f, &ctx);
+				write_midx_large_offsets(f, &ctx);
 				break;
 
 			default:
@@ -1025,9 +1016,9 @@  static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	}
 	stop_progress(&progress);
 
-	if (written != chunk_offsets[num_chunks])
+	if (f->total + f->offset != chunk_offsets[num_chunks])
 		BUG("incorrect final offset %"PRIu64" != %"PRIu64,
-		    written,
+		    f->total + f->offset,
 		    chunk_offsets[num_chunks]);
 
 	finalize_hashfile(f, NULL, CSUM_FSYNC | CSUM_HASH_IN_STREAM);