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

[Honglei Huang <honghuan@amd.com>]

On 2025/11/22 02:00, Dmitry Osipenko wrote:
> On 11/21/25 11:14, Honglei Huang wrote:
>>
>>
>> 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.
> 
> I was previously very puzzled by what bug is fixed and didn't notice it,
> seeing only the err < 0 changes. Now I see which code is fixed after you
> pointed it out explicitly.
> 
> The common practice is:
> 
> 1. Bug fix patches should contain only fixes
> 2. All code improvements should be done in separate patches
> 3. Bugfix patches should be first in the series, improvements follow
> them on top of the fixes
> 
> So here should be two patches:
> 
> 1. The virgl_cmd_resource_create_blob() fix
> 2. virtio_gpu_create_mapping_iov() err handling improvement
> 

You are absolutely correct. I apologize for the confusion in my approach.

Will prepare v5 with this two-patch structure, ensuring the bug fix is 
isolated and can be easily reviewed and backported if needed, while the 
style improvements are clearly separated as code quality enhancements.

Regards,
Honglei