On Sat, Apr 10 2021, Ævar Arnfjörð Bjarmason wrote:
> On Fri, Apr 09 2021, Jeff King wrote:
>
>> 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?:
Sent a bit too soon...:
> 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);
Well, aside from this segfault think-o introduced while
experimenting. Needs to be:
@@ -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)) {
+ if (!obj) {
+ struct blob *blob = create_blob(r, oid);
+ obj = &blob->object;
+ }
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->parsed = 1;
+ return obj;
}
buffer = repo_read_object_file(r, oid, &type, &size);
