Hi Akihiko,
> Subject: Re: [PATCH v6 06/11] virtio-gpu-dmabuf: Improve error
> handling by introducing 'Error **'
>
> >> Make the error handling more robust in virtio_gpu_init_udmabuf()
> >> by passing in 'Error **' parameter to capture errors from
> >> virtio_gpu_create_udmabuf() and virtio_gpu_remap_dmabuf().
> >> And, since they now take in 'Error **' parameter, have them
> >> return a bool to adhere to best practices.
> >>
> >> 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 | 45 ++++++++++++++++++++++-------
> -----
> >> 1 file changed, 30 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/hw/display/virtio-gpu-dmabuf.c b/hw/display/virtio-gpu-
> >> dmabuf.c
> >> index 8d67ef7c2a..d9b2ecaf31 100644
> >> --- a/hw/display/virtio-gpu-dmabuf.c
> >> +++ b/hw/display/virtio-gpu-dmabuf.c
> >> @@ -27,7 +27,8 @@
> >> #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 bool virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res,
> >> + Error **errp)
> >> {
> >> g_autofree struct udmabuf_create_list *list = NULL;
> >> RAMBlock *rb;
> >> @@ -36,7 +37,8 @@ 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 false;
> >> }
> >> list = g_malloc0(sizeof(struct udmabuf_create_list) +
> >> @@ -45,7 +47,10 @@ 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;
> >> + qemu_log_mask(LOG_GUEST_ERROR,
> >> + "%s: Could not find valid ramblock\n",
> >> + __func__);
> >> + return false;
>
> include/qapi/error.h suggests the following error handling pattern:
> > Call a function, receive an error from it, and pass it to the caller
> > - when the function returns a value that indicates failure, say
> > false:
> > if (!foo(arg, errp)) {
> > handle the error...
> > }
>
> Returning false without passing an error to the caller breaks it so
> please don't do that.
That's why I added an additional check in the caller:
if (local_err) {
error_report_err(local_err);
}
Having said that, I am not sure what is the right thing to do here.
IMO, the proper way would be to add error_setg() but you mentioned
doing that would be incorrect given that this is a Guest error.
So, how should I proceed?
>
> >> }
> >> list->list[i].memfd = rb->fd;
> >> @@ -58,20 +63,26 @@ static void virtio_gpu_create_udmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >> res->dmabuf_fd = ioctl(udmabuf, UDMABUF_CREATE_LIST, list);
> >> if (res->dmabuf_fd < 0) {
> >> - warn_report("%s: UDMABUF_CREATE_LIST: %s", __func__,
> >> - strerror(errno));
> >> + error_setg_errno(errp, -res->dmabuf_fd,
> >> + "Could not create dmabuf fd via udmabuf
> >> driver");
> >
> > This is a guest error since it indicates that the guest specified wrong
> > addresses.
I don't have a strong opinion here but my understanding is that this should
not be considered a Guest error because the rb (which we obtained using
Guest addresses) is valid at this point, so the UDMABUF_CREATE_LIST IOCTL
failure should be treated as a Host error.
Regardless, it is not clear how we can precisely determine who (Guest or Host)
is responsible for the failure here and in some other places.
Thanks,
Vivek
> >
> > Regards,
> > Akihiko Odaki
> >
> >> + return false;
> >> }
> >> + return true;
> >> }
> >> -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)
> >> @@ -125,6 +136,7 @@ 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;
> >> @@ -132,12 +144,15 @@ void virtio_gpu_init_dmabuf(struct
> >> virtio_gpu_simple_resource *res)
> >> res->iov[0].iov_len < 4096) {
> >> pdata = res->iov[0].iov_base;
> >> } else {
> >> - virtio_gpu_create_udmabuf(res);
> >> - if (res->dmabuf_fd < 0) {
> >> + if (!virtio_gpu_create_udmabuf(res, &local_err)) {
> >> + if (local_err) {
> >> + error_report_err(local_err);
> >> + }
> >> return;
> >> }
> >> - virtio_gpu_remap_dmabuf(res);
> >> - if (!res->remapped) {
> >> +
> >> + if (!virtio_gpu_remap_dmabuf(res, &local_err)) {
> >> + error_report_err(local_err);
> >> return;
> >> }
> >> pdata = res->remapped;
> >
