Subject: Re: [PATCH v2 2/5] backfill: basic functionality and tests

From: Derrick Stolee <[email-masked]>
Date: Mon, 3 Feb 2025 09:44:49 -0500

On 1/16/25 5:01 AM, Patrick Steinhardt wrote:
> On Fri, Dec 20, 2024 at 04:29:50PM +0000, Derrick Stolee via GitGitGadget wrote:
>> diff --git a/builtin/backfill.c b/builtin/backfill.c
>> index 38e6aaeaa03..177fd4286c7 100644
>> --- a/builtin/backfill.c
>> +++ b/builtin/backfill.c
> [snip]
>> +static int fill_missing_blobs(const char *path UNUSED,
>> +			      struct oid_array *list,
>> +			      enum object_type type,
>> +			      void *data)
>> +{
>> +	struct backfill_context *ctx = data;
>> +
>> +	if (type != OBJ_BLOB)
>> +		return 0;
>> +
>> +	for (size_t i = 0; i < list->nr; i++) {
>> +		off_t size = 0;
>> +		struct object_info info = OBJECT_INFO_INIT;
>> +		info.disk_sizep = &size;
>> +		if (oid_object_info_extended(ctx->repo,
>> +					     &list->oid[i],
>> +					     &info,
>> +					     OBJECT_INFO_FOR_PREFETCH) ||
>> +		    !size)
> 
> So this is the object existence test? Is there a reason why we don't use
> `repo_has_object_file()`, or its `_with_flags()` variant if we need to
> pass `OBJECT_INFO_FOR_PREFETCH`?

You make a good point, but I also notice that repo_has_object_file() has
the following comment:

  * These functions can be removed once all callers have migrated to
  * has_object() and/or oid_object_info_extended().

so I'll use has_object().

>> +			oid_array_append(&ctx->current_batch, &list->oid[i]);
>> +	}
>> +
>> +	if (ctx->current_batch.nr >= ctx->batch_size)
>> +		download_batch(ctx);
>> +
>> +	return 0;
>> +}
>> +
>> +static int do_backfill(struct backfill_context *ctx)
>> +{
>> +	struct rev_info revs;
>> +	struct path_walk_info info = PATH_WALK_INFO_INIT;
>> +	int ret;
>> +
>> +	repo_init_revisions(ctx->repo, &revs, "");
>> +	handle_revision_arg("HEAD", &revs, 0, 0);
>> +
>> +	info.blobs = 1;
>> +	info.tags = info.commits = info.trees = 0;
> 
> Nit: this should be unnecessary as PATH_WALK_INFO_INIT already
> initialized those fields for us, right?

The info.blobs is redundant, but is helpful for context. The
other line is necessary as PATH_WALK_INFO_INIT is defined as:

#define PATH_WALK_INFO_INIT {   \
	.blobs = 1,		\
	.trees = 1,		\
	.commits = 1,		\
	.tags = 1,		\
}

>> +	info.revs = &revs;
>> +	info.path_fn = fill_missing_blobs;
>> +	info.path_fn_data = ctx;
>> +
>> +	ret = walk_objects_by_path(&info);
>> +
>> +	/* Download the objects that did not fill a batch. */
>> +	if (!ret)
>> +		download_batch(ctx);
>> +
>> +	backfill_context_clear(ctx);
> 
> Nit: I think it's a bit funny that we're cleaning up the context over
> here rather than in the caller.
Cleaning up in the caller makes the "return do_backfill(&ctx);" line
slightly more complicated, but you are right that we shouldn't be
cleaning up something that the method "doesn't own".

Thanks,
-Stolee