[v3] virtio-gpu: use consistent error checking style for virtio_gpu_create_mapping_iov

[Honglei Huang]

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 incorrectly checking 'if (!ret)' for
error conditions.

Change all virtio_gpu_create_mapping_iov() error checks to use 'if (ret < 0)'
instead of 'if (ret != 0)', 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()

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 <hongh...@amd.com>
Reviewed-by: Akihiko Odaki <od...@rsg.ci.i.u-tokyo.ac.jp>
---
 hw/display/virtio-gpu-virgl.c | 4 ++--
 hw/display/virtio-gpu.c       | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

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;
     }
-- 
2.34.1