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?
Any further thoughts/comments here and below?
Thanks,
Vivek
>
> >
> > >> }
> > >> 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;
> > >
>
