Re: [PATCH 1/2] blob.c: remove buffer & size arguments to parse_blob_buffer()
On Fri, Apr 09 2021, Jeff King wrote:
Show 69 quoted lines
> On Fri, Apr 09, 2021 at 10:07:27AM +0200, Ævar Arnfjörð Bjarmason wrote:
>
>> As noted in the comment introduced in 837d395a5c0 (Replace
>> parse_blob() with an explanatory comment, 2010-01-18) the old
>> parse_blob() function and the current parse_blob_buffer() exist merely
>> to provide consistency in the API.
>>
>> We're not going to parse blobs like we "parse" commits, trees or
>> tags. So let's not have the parse_blob_buffer() take arguments that
>> pretends that we do. Its only use is to set the "parsed" flag.
>>
>> See bd2c39f58f9 ([PATCH] don't load and decompress objects twice with
>> parse_object(), 2005-05-06) for the introduction of parse_blob_buffer().
>
> OK. Calling it parse_blob_buffer() is a little silly since it doesn't
> even take a buffer anymore. But I guess parse_blob() might imply that it
> actually loads the contents from disk to check them (which the other
> parse_foo() functions do), so that's not a good name.
>
> So this might be the least bad thing. Given that there are only two
> callers, just setting blob->object.parsed might not be unreasonable,
> either. But I don't think it's worth spending too much time on.
>
>> @@ -266,7 +266,7 @@ struct object *parse_object(struct repository *r, const struct object_id *oid)
>> error(_("hash mismatch %s"), oid_to_hex(oid));
>> return NULL;
>> }
>> - parse_blob_buffer(lookup_blob(r, oid), NULL, 0);
>> + parse_blob_buffer(lookup_blob(r, oid));
>> return lookup_object(r, oid);
>
> Not new in your patch, but I wondered if this could cause a segfault
> when lookup_blob() returns NULL. I _think_ the answer is "no". We'd hit
> this code path when either:
>
> - lookup_object() returns an object with type OBJ_BLOB, in which case
> lookup_blob() would return that same object
>
> - lookup_object() returned NULL, in which case lookup_blob() will call
> it again, get NULL again, and then auto-create the blob and return
> it
>
> So I think it is OK. But there are a bunch of duplicate hash lookups in
> this code. It would be clearer and more efficient as:
>
> diff --git a/object.c b/object.c
> index 2c32691dc4..2dfa038f13 100644
> --- a/object.c
> +++ b/object.c
> @@ -262,12 +262,14 @@ struct object *parse_object(struct repository *r, const struct object_id *oid)
> if ((obj && obj->type == OBJ_BLOB && repo_has_object_file(r, oid)) ||
> (!obj && repo_has_object_file(r, oid) &&
> oid_object_info(r, oid, NULL) == OBJ_BLOB)) {
> + if (!obj)
> + obj = create_object(r, oid, alloc_blob_node(r));
> if (check_object_signature(r, repl, NULL, 0, NULL) < 0) {
> error(_("hash mismatch %s"), oid_to_hex(oid));
> return NULL;
> }
> - parse_blob_buffer(lookup_blob(r, oid), NULL, 0);
> - return lookup_object(r, oid);
> + parse_blob_buffer(obj, NULL, 0);
> + return obj;
> }
>
> buffer = repo_read_object_file(r, oid, &type, &size);
>
> but I doubt the efficiency matters much in practice. Those hash lookups
> will be lost in the noise of computing the hash of the blob contents.I was trying to keep the changes smaller, but what about just doing this?:
diff --git a/blob.c b/blob.c
index 182718aba9..69293e7d8e 100644
--- a/blob.c
+++ b/blob.c
@@ -5,16 +5,16 @@
const char *blob_type = "blob";
+struct blob *create_blob(struct repository *r, const struct object_id *oid)
+{
+ return create_object(r, oid, alloc_blob_node(r));
+}
+
struct blob *lookup_blob(struct repository *r, const struct object_id *oid)
{
struct object *obj = lookup_object(r, oid);
if (!obj)
- return create_object(r, oid, alloc_blob_node(r));
- return object_as_type(obj, OBJ_BLOB, 0);
-}
+ return create_blob(r, oid);
-int parse_blob_buffer(struct blob *item, void *buffer, unsigned long size)
-{
- item->object.parsed = 1;
- return 0;
+ return object_as_type(obj, OBJ_BLOB, 0);
}
diff --git a/blob.h b/blob.h
index 1664872055..ad34f0e9cc 100644
--- a/blob.h
+++ b/blob.h
@@ -9,10 +9,9 @@ struct blob {
struct object object;
};
+struct blob *create_blob(struct repository *r, const struct object_id *oid);
struct blob *lookup_blob(struct repository *r, const struct object_id *oid);
-int parse_blob_buffer(struct blob *item, void *buffer, unsigned long size);
-
/**
* Blobs do not contain references to other objects and do not have
* structured data that needs parsing. However, code may use the
diff --git a/object.c b/object.c
index 78343781ae..2699431404 100644
--- a/object.c
+++ b/object.c
@@ -195,8 +195,7 @@ struct object *parse_object_buffer(struct repository *r, const struct object_id
if (type == OBJ_BLOB) {
struct blob *blob = lookup_blob(r, oid);
if (blob) {
- if (parse_blob_buffer(blob, buffer, size))
- return NULL;
+ blob->object.parsed = 1;
obj = &blob->object;
}
} else if (type == OBJ_TREE) {
@@ -262,12 +261,16 @@ struct object *parse_object(struct repository *r, const struct object_id *oid)
if ((obj && obj->type == OBJ_BLOB && repo_has_object_file(r, oid)) ||
(!obj && repo_has_object_file(r, oid) &&
oid_object_info(r, oid, NULL) == OBJ_BLOB)) {
+ struct blob *blob;
+ if (!obj)
+ blob = create_blob(r, oid);
if (check_object_signature(r, repl, NULL, 0, NULL) < 0) {
error(_("hash mismatch %s"), oid_to_hex(oid));
return NULL;
}
- parse_blob_buffer(lookup_blob(r, oid), NULL, 0);
- return lookup_object(r, oid);
+ obj = &blob->object;
+ obj->parsed = 1;
+ return obj;
}
buffer = repo_read_object_file(r, oid, &type, &size);
Ævar Arnfjörð Bjarmason <avarab@gmail.com>