Re: [v4] virtio-gpu: use consistent error checking style for virtio_gpu_create_mapping_iov

[Honglei Huang <honghuan@amd.com>]

On 2025/11/21 15:58, Honglei Huang wrote:
> Fix error handling logic in virgl_cmd_resource_create_blob and improve
> consistency across the codebase.
> 
> virtio_gpu_create_mapping_iov() returns 0 on success and negative values
> on error, but the original code was inconsistently checking for error
> conditions using different patterns.
> 
> Change all virtio_gpu_create_mapping_iov() error checks to use consistent
> 'ret < 0' or 'ret >= 0' patterns, following the preferred QEMU coding
> convention for functions that return 0 on success and negative on error.
> This makes the return value convention immediately clear to code readers
> without needing to look up the function definition.
> 
> Updated locations:
> - hw/display/virtio-gpu-virgl.c: virgl_cmd_resource_create_blob()
> - hw/display/virtio-gpu-virgl.c: virgl_cmd_resource_attach_backing()
> - hw/display/virtio-gpu.c: virtio_gpu_resource_create_blob()
> - hw/display/virtio-gpu.c: virtio_gpu_resource_attach_backing()
> - hw/display/virtio-gpu-rutabaga.c: rutabaga_cmd_attach_backing()
> - hw/display/virtio-gpu-rutabaga.c: rutabaga_cmd_resource_create_blob()
> 
> Changes since v3:
> - Extended consistency improvements to virtio-gpu-rutabaga.c
> - Changed CHECK(!ret) to CHECK(ret >= 0) and CHECK(!result) to
>    CHECK(result >= 0) in rutabaga functions for consistency
> - Now covers all virtio-gpu files that use virtio_gpu_create_mapping_iov()
> 
> Changes since v2:
> - Use 'if (ret < 0)' instead of 'if (ret != 0)' following maintainer's
>    feedback on preferred QEMU coding style for error checking functions
>    that return 0 on success and negative on error
> - Updated all similar usages across virtio-gpu files for consistency
> - Expanded scope from single function fix to codebase-wide style consistency
> 
> Fixes: 7c092f17ccee ("virtio-gpu: Handle resource blob commands")
> Signed-off-by: Honglei Huang <honghuan@amd.com>
> Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> ---
>   hw/display/virtio-gpu-rutabaga.c | 4 ++--
>   hw/display/virtio-gpu-virgl.c    | 4 ++--
>   hw/display/virtio-gpu.c          | 4 ++--
>   3 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/display/virtio-gpu-rutabaga.c b/hw/display/virtio-gpu-rutabaga.c
> index ed5ae52acb..ea2928b706 100644
> --- a/hw/display/virtio-gpu-rutabaga.c
> +++ b/hw/display/virtio-gpu-rutabaga.c
> @@ -466,7 +466,7 @@ rutabaga_cmd_attach_backing(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
>   
>       ret = virtio_gpu_create_mapping_iov(g, att_rb.nr_entries, sizeof(att_rb),
>                                           cmd, NULL, &res->iov, &res->iov_cnt);
> -    CHECK(!ret, cmd);
> +    CHECK(ret >= 0, cmd);
>   
>       vecs.iovecs = res->iov;
>       vecs.num_iovecs = res->iov_cnt;
> @@ -616,7 +616,7 @@ rutabaga_cmd_resource_create_blob(VirtIOGPU *g,
>           result = virtio_gpu_create_mapping_iov(g, cblob.nr_entries,
>                                                  sizeof(cblob), cmd, &res->addrs,
>                                                  &res->iov, &res->iov_cnt);
> -        CHECK(!result, cmd);
> +        CHECK(result >= 0, cmd);
>       }
>   
>       rc_blob.blob_id = cblob.blob_id;
> diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
> index 94ddc01f91..6ebd9293e5 100644
> --- a/hw/display/virtio-gpu-virgl.c
> +++ b/hw/display/virtio-gpu-virgl.c
> @@ -557,7 +557,7 @@ static void virgl_resource_attach_backing(VirtIOGPU *g,
>   
>       ret = virtio_gpu_create_mapping_iov(g, att_rb.nr_entries, sizeof(att_rb),
>                                           cmd, NULL, &res_iovs, &res_niov);
> -    if (ret != 0) {
> +    if (ret < 0) {
>           cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
>           return;
>       }
> @@ -701,7 +701,7 @@ static void virgl_cmd_resource_create_blob(VirtIOGPU *g,
>           ret = virtio_gpu_create_mapping_iov(g, cblob.nr_entries, sizeof(cblob),
>                                               cmd, &res->base.addrs,
>                                               &res->base.iov, &res->base.iov_cnt);
> -        if (!ret) {
> +        if (ret < 0) {
>               cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
>               return;
>           }
> diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
> index 0a1a625b0e..1038c6a49f 100644
> --- a/hw/display/virtio-gpu.c
> +++ b/hw/display/virtio-gpu.c
> @@ -352,7 +352,7 @@ static void virtio_gpu_resource_create_blob(VirtIOGPU *g,
>       ret = virtio_gpu_create_mapping_iov(g, cblob.nr_entries, sizeof(cblob),
>                                           cmd, &res->addrs, &res->iov,
>                                           &res->iov_cnt);
> -    if (ret != 0) {
> +    if (ret < 0) {
>           cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
>           g_free(res);
>           return;
> @@ -931,7 +931,7 @@ virtio_gpu_resource_attach_backing(VirtIOGPU *g,
>   
>       ret = virtio_gpu_create_mapping_iov(g, ab.nr_entries, sizeof(ab), cmd,
>                                           &res->addrs, &res->iov, &res->iov_cnt);
> -    if (ret != 0) {
> +    if (ret < 0) {
>           cmd->error = VIRTIO_GPU_RESP_ERR_UNSPEC;
>           return;
>       }

This v4 patch started as a bug fix for error handling in 
`virgl_cmd_resource_create_blob()` but evolved through community 
feedback to include comprehensive code style consistency improvements, 
unifying error checking patterns (`ret < 0`) across all virtio-gpu files.

  This version appears to have gained community consensus and may be 
ready for acceptance.

Correct me if I am wrong.

Regards,
Honglei