From: Justin Tobler <jltobler@gmail.com>
Date: Mon, 09 Feb 2026 19:57:44 GMT
Subject: Re: [PATCH 1/3] builtin/backfill: fix flags passed to `odb_has_object()`
Message-ID: <aYo5M7YLqroH4fab@denethor>
In-Reply-To: <20260126-b4-pks-read-object-info-flags-v1-1-e682a003b17c@pks.im>

On 26/01/26 01:17PM, Patrick Steinhardt wrote:
> The function `fill_missing_blobs()` receives an array of object IDs and
> verifies for each of them whether the corresponding object exists. If it
> doesn't exist, we add it to a set of objects and then batch-fetch all of
> the objects at once.
> 
> The check for whether or not we already have the object is broken
> though: we pass `OBJECT_INFO_FOR_PREFETCH`, but `odb_has_object()`
> expects us to pass `HAS_OBJECT_*` flags.

Ok so the flag we are passing to `odb_has_object()` here is not from the
expected set.

> The flag expands to:
> 
>   - `OBJECT_INFO_QUICK`, which asks the object database to not reprepare
>     in case the object wasn't found. This makes sense, as we'd otherwise
>     reprepare the object database as many times as we have missing
>     objects.
> 
>   - `OBJECT_INFO_SKIP_FETCH_OBJECT`, which asks the object database to
>     not fetch the object in case it's missing. Again, this makes sense,
>     as we want to batch-fetch the objects.
> 
> This shows that we indeed want the equivalent of this flag, but of
> course represented as `HAS_OBJECT_*` flags.
> 
> Luckily, the code is already working correctly. The `OBJECT_INFO` flag
> expands to `(1 << 3) | (1 << 4)`, none of which are valid `HAS_OBJECT`
> flags. And if no flags are passed, `odb_has_object()` ends up calling
> `odb_read_object_info_extended()` with exactly the above two flags that
> we wanted to set in the first place.

Lucky indeed.

> Of course, this is pure luck, and this can break any moment. So let's
> fix this and correct the code to not pass any flags at all.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  builtin/backfill.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/builtin/backfill.c b/builtin/backfill.c
> index e80fc1b694..d8cb3b0eba 100644
> --- a/builtin/backfill.c
> +++ b/builtin/backfill.c
> @@ -67,8 +67,7 @@ static int fill_missing_blobs(const char *path UNUSED,
>  		return 0;
>  
>  	for (size_t i = 0; i < list->nr; i++) {
> -		if (!odb_has_object(ctx->repo->objects, &list->oid[i],
> -				    OBJECT_INFO_FOR_PREFETCH))
> +		if (!odb_has_object(ctx->repo->objects, &list->oid[i], 0))

By passing 0 as the flag value here, the underlying
`odb_read_object_info_extended()` gets both the `OBJECT_INFO_QUICK` and
`OBJECT_INFO_SKIP_FETCH_OBJECT` flags set. This is exactly what we want
so there is no need to add an additional `HAS_OBJECT_*` flag. Looks
good.

-Justin