Re: [PATCH v12 09/10] virtio-gpu-dmabuf: Improve error handling with 'Error **' and err enum

["Cédric Le Goater" <clg@redhat.com>]

On 3/19/26 06:15, Vivek Kasireddy wrote:
> Make the error handling more robust in virtio_gpu_init_udmabuf()
> by introducing 'Error **' parameter to capture errors and using
> an enum from VFIO to categorize different errors. This allows for
> better error reporting and handling of errors from
> virtio_gpu_create_udmabuf() and virtio_gpu_remap_dmabuf().
> 
> Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Cc: Alex Williamson <alex@shazbot.org>
> Cc: Cédric Le Goater <clg@redhat.com>
> Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>   hw/display/virtio-gpu-dmabuf.c | 67 +++++++++++++++++++++++-----------
>   1 file changed, 45 insertions(+), 22 deletions(-)
> 
> diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-dmabuf.c
> index e35f7714a9..89aa487654 100644
> --- a/hw/display/virtio-gpu-dmabuf.c
> +++ b/hw/display/virtio-gpu-dmabuf.c
> @@ -18,6 +18,7 @@
>   #include "ui/console.h"
>   #include "hw/virtio/virtio-gpu.h"
>   #include "hw/virtio/virtio-gpu-pixman.h"
> +#include "hw/vfio/vfio-device.h"
>   #include "trace.h"
>   #include "system/ramblock.h"
>   #include "system/hostmem.h"
> @@ -27,16 +28,18 @@
>   #include "standard-headers/linux/udmabuf.h"
>   #include "standard-headers/drm/drm_fourcc.h"
>   
> -static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res)
> +static int virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res,
> +                                     Error **errp)
>   {
>       g_autofree struct udmabuf_create_list *list = NULL;
>       RAMBlock *rb;
>       ram_addr_t offset;
> -    int udmabuf, i;
> +    int udmabuf, i, fd;
>   
>       udmabuf = udmabuf_fd();
>       if (udmabuf < 0) {
> -        return;
> +        error_setg(errp, "udmabuf device not available or enabled");
> +        return VFIO_DMABUF_CREATE_ERR_UNSPEC;

The function virtio_gpu_create_udmabuf() is returning VFIO_DMABUF_* enum
values, which is problematic because the function creates a udmabuf, not
a VFIO dmabuf.

This creates a layering violation. The virtio-gpu-dmabuf code (which
handles both udmabuf and VFIO dmabuf creation) is using error codes
defined in the VFIO-specific header.

Please find another solution.



>       }
>   
>       list = g_malloc0(sizeof(struct udmabuf_create_list) +
> @@ -45,7 +48,8 @@ static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res)
>       for (i = 0; i < res->iov_cnt; i++) {
>           rb = qemu_ram_block_from_host(res->iov[i].iov_base, false, &offset);
>           if (!rb || rb->fd < 0) {
> -            return;
> +            error_setg(errp, "IOV memory address incompatible with udmabuf ");
> +            return VFIO_DMABUF_CREATE_ERR_INVALID_IOV;
>           }
>   
>           list->list[i].memfd  = rb->fd;
> @@ -56,22 +60,28 @@ static void virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res)
>       list->count = res->iov_cnt;
>       list->flags = UDMABUF_FLAGS_CLOEXEC;
>   
> -    res->dmabuf_fd = ioctl(udmabuf, UDMABUF_CREATE_LIST, list);
> -    if (res->dmabuf_fd < 0) {
> -        warn_report("%s: UDMABUF_CREATE_LIST: %s", __func__,
> -                    strerror(errno));
> +    fd = ioctl(udmabuf, UDMABUF_CREATE_LIST, list);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "UDMABUF_CREATE_LIST: ioctl failed");
> +        if (errno == EINVAL || errno == EBADFD) {
> +            return VFIO_DMABUF_CREATE_ERR_INVALID_IOV;
> +        }
> +        return VFIO_DMABUF_CREATE_ERR_UNSPEC;
>       }
> +    return fd;
>   }
>   
> -static void virtio_gpu_remap_dmabuf(struct virtio_gpu_simple_resource *res)
> +static void *virtio_gpu_remap_dmabuf(struct virtio_gpu_simple_resource *res,
> +                                     Error **errp)
>   {
> -    res->remapped = mmap(NULL, res->blob_size, PROT_READ,
> -                         MAP_SHARED, res->dmabuf_fd, 0);
> -    if (res->remapped == MAP_FAILED) {
> -        warn_report("%s: dmabuf mmap failed: %s", __func__,
> -                    strerror(errno));
> -        res->remapped = NULL;
> +    void *map;
> +
> +    map = mmap(NULL, res->blob_size, PROT_READ, MAP_SHARED, res->dmabuf_fd, 0);
> +    if (map == MAP_FAILED) {
> +        error_setg_errno(errp, errno, "dmabuf mmap failed");
> +        return NULL;
>       }
> +    return map;
>   }
>   
>   static void virtio_gpu_destroy_dmabuf(struct virtio_gpu_simple_resource *res)
> @@ -125,22 +135,35 @@ bool virtio_gpu_have_udmabuf(void)
>   
>   void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
>   {
> +    Error *local_err = NULL;
>       void *pdata = NULL;
>   
> -    res->dmabuf_fd = -1;
>       if (res->iov_cnt == 1 &&
>           res->iov[0].iov_len < 4096) {
> +        res->dmabuf_fd = -1;
>           pdata = res->iov[0].iov_base;
>       } else {
> -        virtio_gpu_create_udmabuf(res);
> +        res->dmabuf_fd = virtio_gpu_create_udmabuf(res, &local_err);
> +        if (res->dmabuf_fd == VFIO_DMABUF_CREATE_ERR_INVALID_IOV) {
> +            error_free_or_abort(&local_err);

Why not report the error in the QEMU log below ?

> +
> +            qemu_log_mask(LOG_GUEST_ERROR,
> +                          "Cannot create dmabuf: incompatible memory\n");
> +            return;
> +        } else if (res->dmabuf_fd >= 0) {
> +            pdata = virtio_gpu_remap_dmabuf(res, &local_err);
> +            if (!pdata) {
> +                virtio_gpu_destroy_dmabuf(res);
> +            }
> +        } else {
> +            res->dmabuf_fd = -1;
> +        }
> +
>           if (res->dmabuf_fd < 0) {
> +            error_report_err(local_err);
>               return;
>           }
> -        virtio_gpu_remap_dmabuf(res);
> -        if (!res->remapped) {
> -            return;
> -        }
> -        pdata = res->remapped;
> +        res->remapped = pdata;
>       }
>   
>       res->blob = pdata;