Re: AIO v2.5 - Mailing list pgsql-hackers

Hi,

On 2025-04-03 13:46:39 -0300, Ranier Vilela wrote:
> Em qua., 2 de abr. de 2025 às 08:58, Andres Freund <andres@anarazel.de>
> escreveu:
>
> > Hi,
> >
> > I've pushed fixes for 1) and 2) and am working on 3).
> >
> Coverity has one report about this.
>
> CID 1596092: (#1 of 1): Uninitialized scalar variable (UNINIT)
> 13. uninit_use_in_call: Using uninitialized value result_one. Field
> result_one.result is uninitialized when calling pgaio_result_report.

Isn't this a rather silly thing to warn about for coverity?

  The field isn't
used in pgaio_result_report().  It can't be a particularly rare thing to have
struct fields that aren't always used?

> Below not is a fix, but some suggestion:
>
> diff --git a/src/backend/storage/buffer/bufmgr.c
> b/src/backend/storage/buffer/bufmgr.c
> index 1c37d7dfe2..b0f9ce452c 100644
> --- a/src/backend/storage/buffer/bufmgr.c
> +++ b/src/backend/storage/buffer/bufmgr.c
> @@ -6786,6 +6786,8 @@ buffer_readv_encode_error(PgAioResult *result,
>   else
>   result->status = PGAIO_RS_WARNING;
>
> + result->result = 0;
> +

That'd be completely wrong - and the tests indeed fail if you do that. The
read might succeed with a warning (e.g. due to zero_damaged_pages) in which
case the result still carries important information about how many blocks were
successfully read.

>   /*
>   * The encoding is complicated enough to warrant cross-checking it against
>   * the decode function.
> @@ -6868,8 +6870,6 @@ buffer_readv_complete_one(PgAioTargetData *td, uint8
> buf_off, Buffer buffer,
>   /* Check for garbage data. */
>   if (!failed)
>   {
> - PgAioResult result_one;
> -
>   if (!PageIsVerified((Page) bufdata, tag.blockNum, piv_flags,
>   failed_checksum))
>   {
> @@ -6904,6 +6904,8 @@ buffer_readv_complete_one(PgAioTargetData *td, uint8
> buf_off, Buffer buffer,
>   */
>   if (*buffer_invalid || *failed_checksum || *zeroed_buffer)
>   {
> + PgAioResult result_one;
> +
>   buffer_readv_encode_error(&result_one, is_temp,
>    *zeroed_buffer,
>    *ignored_checksum,
>
>
> 1. I couldn't find the correct value to initialize the *result* field.

It is not accessed in this path.  I guess we can just zero-initialize
result_one to shut up coverity.

> 2. result_one can be reduced scope.

True.