Hi Akihiko,
> Subject: Re: [PATCH v7 06/10] virtio-gpu-dmabuf: Improve error
> handling with 'Error **' and err enum
>
> On 2026/02/23 17:00, Vivek Kasireddy wrote:
> > Make the error handling more robust in virtio_gpu_init_udmabuf()
> > by introducing 'Error **' parameter to capture errors and an enum
> > 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 | 65 +++++++++++++++++++++++++---
> ------
> > 1 file changed, 48 insertions(+), 17 deletions(-)
> >
> > diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
> dmabuf.c
> > index 8d67ef7c2a..fdcf8e53a2 100644
> > --- a/hw/display/virtio-gpu-dmabuf.c
> > +++ b/hw/display/virtio-gpu-dmabuf.c
> > @@ -27,7 +27,17 @@
> > #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)
> > +typedef enum VirtIOGPUErrorType {
> > + VIRTIO_GPU_NO_ERROR = 0,
> > + /* Guest is responsible for this error */
> > + VIRTIO_GPU_GUEST_ERROR = 1,
> > + /* Host is at fault for this error */
> > + VIRTIO_GPU_HOST_ERROR = 2,
>
> include/qapi/error.h says:
> > - Whenever practical, also return a value that indicates success /
> > failure. This can make the error checking more concise, and can
> > avoid useless error object creation and destruction. Note that
> > we still have many functions returning void. We recommend
> > . bool-valued functions return true on success / false on failure,
> > . pointer-valued functions return non-null / null pointer, and
> > . integer-valued functions return non-negative / negative.
>
> Do what it says. Non-negative if *errp is set. Negative otherwise.
Ok, I'll change the values in the following way:
typedef enum VirtIOGPUErrorType {
VIRTIO_GPU_NO_ERROR = 1,
/* Guest is responsible for this error */
VIRTIO_GPU_GUEST_ERROR = -1,
/* Host is at fault for this error */
VIRTIO_GPU_HOST_ERROR = -2,
} VirtIOGPUErrorType;
>
> > +} VirtIOGPUErrorType;
> > +
> > +static VirtIOGPUErrorType
> > +virtio_gpu_create_udmabuf(struct virtio_gpu_simple_resource *res,
> int *fd,
> > + Error **errp)
> > {
> > g_autofree struct udmabuf_create_list *list = NULL;
> > RAMBlock *rb;
> > @@ -36,7 +46,8 @@ static void virtio_gpu_create_udmabuf(struct
> virtio_gpu_simple_resource *res)
> >
> > udmabuf = udmabuf_fd();
> > if (udmabuf < 0) {
> > - return;
> > + error_setg(errp, "udmabuf device not available");
> > + return VIRTIO_GPU_HOST_ERROR;
> > }
> >
> > list = g_malloc0(sizeof(struct udmabuf_create_list) +
> > @@ -45,7 +56,8 @@ 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, "Could not find valid ramblock");
>
> It is a valid ramblock even if rb->fd < 0. It is just "incompatible"
> with udmabuf.
Does "IOV memory address incompatible with udmabuf " sound better?
>
> > + return VIRTIO_GPU_GUEST_ERROR;
> > }
> >
> > list->list[i].memfd = rb->fd;
> > @@ -56,22 +68,30 @@ 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 VIRTIO_GPU_GUEST_ERROR;
> > + }
> > + return VIRTIO_GPU_HOST_ERROR;
> > }
> > + return VIRTIO_GPU_NO_ERROR;
> > }
> >
> > -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 +145,30 @@ bool virtio_gpu_have_udmabuf(void)
> >
> > void virtio_gpu_init_dmabuf(struct virtio_gpu_simple_resource *res)
> > {
> > + Error *local_err = NULL;
> > + VirtIOGPUErrorType err;
> > void *pdata = NULL;
> > + int fd;
> >
> > 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) {
> > + err = virtio_gpu_create_udmabuf(res, &fd, &local_err);
> > + if (err != VIRTIO_GPU_NO_ERROR) {
> > + error_prepend(&local_err, "Cannot create dmabuf: ");
> > + if (err == VIRTIO_GPU_GUEST_ERROR) {
> > + qemu_log_mask(LOG_GUEST_ERROR,
> > + "Cannot create dmabuf: incompatible mem\n");
>
> s/mem/memory/
>
> The log is not that long so we can have a full correct spelling.
It was going over the 80 char limit and I was reluctant to split it
across lines.
>
> > + }
> > + error_report_err(local_err);
>
> This prints a message even for a guest error.
This is intentional. My thinking is that if the user did not enable logging
then it will fail silently in the case of Guest error. So, I thought it makes
sense to print an error regardless of the type of error.
Thanks,
Vivek
>
> Regards,
> Akihiko Odaki
>
> > return;
> > }
> > - virtio_gpu_remap_dmabuf(res);
> > - if (!res->remapped) {
> > +
> > + res->dmabuf_fd = fd;
> > + if (!virtio_gpu_remap_dmabuf(res, &local_err)) {
> > + error_report_err(local_err);
> > return;
> > }
> > pdata = res->remapped;
