Hi Akihiko,
> Subject: Re: [PATCH v8 09/10] virtio-gpu-dmabuf: Improve error handling
> with 'Error **' and err enum
>
> On 2026/02/28 7:13, 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 Guest and Host 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 <[email protected]>
> > Cc: Alex Bennée <[email protected]>
> > Cc: Akihiko Odaki <[email protected]>
> > Cc: Dmitry Osipenko <[email protected]>
> > Cc: Alex Williamson <[email protected]>
> > Cc: Cédric Le Goater <[email protected]>
> > Signed-off-by: Vivek Kasireddy <[email protected]>
> > ---
> > hw/display/virtio-gpu-dmabuf.c | 61 ++++++++++++++++++++++++-------
> ---
> > 1 file changed, 43 insertions(+), 18 deletions(-)
> >
> > diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
> dmabuf.c
> > index 8d67ef7c2a..b2badfc1bd 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_HOST_ERROR;
>
> I failed to point out one thing for naming of the enum. The name should
> express if the error is caused by invalid iov or something else. Then
> virtio-gpu decides how to recover the error; it's virtio-gpu who knows
> the iov is from the guest and decides to report a guest error, not vfio.
> Otherwise, it reports a host error.
So, it sounds like you are suggesting that there needs to be three enum
values:
enum {
/* Guest is responsible for this error */
VFIO_DMABUF_CREATE_GUEST_ERROR = -1,
/* Guest is at fault as the IOVEC passed in is invalid */
VFIO_DMABUF_CREATE_INVALID_IOV_ERROR = -2,
/* Host is at fault for this error */
VFIO_DMABUF_CREATE_HOST_ERROR = -3,
}
Or, please let me know in detail what changes you would like to see.
>
> > }
> >
> > 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_GUEST_ERROR;
> > }
> >
> > list->list[i].memfd = rb->fd;
> > @@ -56,22 +60,30 @@ 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_GUEST_ERROR;
> > + }
> > + return VFIO_DMABUF_CREATE_HOST_ERROR;
> > }
> > + return fd;
> > }
> >
> > -static void virtio_gpu_remap_dmabuf(struct
> virtio_gpu_simple_resource *res)
> > +static bool 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));
> > + 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");
> > res->remapped = NULL;
> > + return false;
> > }
> > + res->remapped = map;
> > + return true;
> > }
> >
> > static void virtio_gpu_destroy_dmabuf(struct
> virtio_gpu_simple_resource *res)
> > @@ -125,19 +137,32 @@ bool virtio_gpu_have_udmabuf(void)
> >
> > void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
> > {
> > + Error *local_err = NULL;
> > void *pdata = NULL;
> > + int ret;
> >
> > res->dmabuf_fd = -1;
> > if (res->iov_cnt == 1 &&
> > res->iov[0].iov_len < 4096) {
> > pdata = res->iov[0].iov_base;
> > } else {
> > - virtio_gpu_create_udmabuf(res);
> > - if (res->dmabuf_fd < 0) {
> > + ret = virtio_gpu_create_udmabuf(res, &local_err);
> > + if (ret < 0) {
> > + error_prepend(&local_err, "Cannot create dmabuf: ");
>
> This error_prepend() is redundant. The error messages
> virtio_gpu_create_udmabuf() emits already suggests they are problems
> with DMA-BUF.
Ok, I'll drop the error_prepend().
Thanks,
Vivek
>
> Regards,
> Akihiko Odaki
>
> > +
> > + if (ret == VFIO_DMABUF_CREATE_GUEST_ERROR) {
> > + qemu_log_mask(LOG_GUEST_ERROR,
> > + "Cannot create dmabuf: incompatible
> > memory\n");
> > + error_free(local_err);
> > + return;
> > + }
> > + error_report_err(local_err);
> > return;
> > }
> > - virtio_gpu_remap_dmabuf(res);
> > - if (!res->remapped) {
> > +
> > + res->dmabuf_fd = ret;
> > + if (!virtio_gpu_remap_dmabuf(res, &local_err)) {
> > + error_report_err(local_err);
> > return;
> > }
> > pdata = res->remapped;
