On Mon, 25 Jan 2021 13:01:12 -0500
Vivek Goyal <vgo...@redhat.com> wrote:
> Right now slave_read() is called through main event loop and does not
> return error. In next few patches I want to call slave_read() from
> vhost device shutdown path as well and want to know if an error
> happened so that caller can give up and return error accordingly.
>
> Hence, create helper function do_slave_read(), which returns an
> integer. Success is 0 and negative number is error code. slave_read()
> calls do_slave_read() and ignores error code.
>
> Signed-off-by: Vivek Goyal <vgo...@redhat.com>
> ---
> hw/virtio/vhost-user.c | 43 ++++++++++++++++++++++++++++++++++++------
> 1 file changed, 37 insertions(+), 6 deletions(-)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index d95dbc39e3..867cac034f 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -1401,7 +1401,7 @@ static uint64_t
> vhost_user_slave_handle_vring_host_notifier(
> return false;
> }
>
> -static void slave_read(void *opaque)
> +static int do_slave_read(void *opaque)
> {
> struct vhost_dev *dev = opaque;
> struct vhost_user *u = dev->opaque;
> @@ -1432,13 +1432,22 @@ static void slave_read(void *opaque)
> size = recvmsg(u->slave_fd, &msgh, 0);
> } while (size < 0 && (errno == EINTR || errno == EAGAIN));
>
> - if (size != VHOST_USER_HDR_SIZE) {
> + if (size < 0) {
> + ret = -errno;
> error_report("Failed to read from slave.");
> goto err;
> }
>
> + if (size != VHOST_USER_HDR_SIZE) {
> + error_report("Failed to read %lu bytes from slave.",
> + VHOST_USER_HDR_SIZE);
Maybe also print size ?
And, question from a newbie : any idea why short reads are
considered as errors instead of retrying ? Same question
stands for the other locations where we check the numbers
of read/written bytes in this function.
> + ret = -EBADMSG;
> + goto err;
> + }
> +
> if (msgh.msg_flags & MSG_CTRUNC) {
> error_report("Truncated message.");
> + ret = -EBADMSG;
> goto err;
> }
>
> @@ -1456,6 +1465,7 @@ static void slave_read(void *opaque)
> error_report("Failed to read msg header."
> " Size %d exceeds the maximum %zu.", hdr.size,
> VHOST_USER_PAYLOAD_SIZE);
> + ret = -EBADMSG;
> goto err;
> }
>
> @@ -1464,8 +1474,15 @@ static void slave_read(void *opaque)
> size = read(u->slave_fd, &payload, hdr.size);
> } while (size < 0 && (errno == EINTR || errno == EAGAIN));
>
> - if (size != hdr.size) {
> + if (size == -1) {
Maybe make it (size < 0) for consistency with the error checking
added above ? And this seems to be the preferred way in the QEMU
tree :)
> error_report("Failed to read payload from slave.");
> + ret = errno;
ret = -errno;
And this should be done before error_report() to ensure errno
isn't cloberred.
> + goto err;
> + }
> +
> + if (size != hdr.size) {
> + error_report("Failed to read %d payload bytes from slave.",
> hdr.size);
> + ret = -EBADMSG;
> goto err;
> }
>
> @@ -1529,13 +1546,22 @@ static void slave_read(void *opaque)
> size = writev(u->slave_fd, iovec, ARRAY_SIZE(iovec));
> } while (size < 0 && (errno == EINTR || errno == EAGAIN));
>
> - if (size != VHOST_USER_HDR_SIZE + hdr.size) {
> + if (size == -1) {
size < 0
> error_report("Failed to send msg reply to slave.");
> + ret = -errno;
Move before error_report()
> + goto err;
> + }
> +
> + if (size != VHOST_USER_HDR_SIZE + hdr.size) {
> + error_report("Failed to send msg reply to slave. Wrote %d bytes"
> + " expected %lu bytes.", size,
> + VHOST_USER_HDR_SIZE + hdr.size);
> + ret = -EIO;
> goto err;
> }
> }
>
> - return;
> + return 0;
>
> err:
> qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
> @@ -1546,7 +1572,12 @@ err:
> close(fd[i]);
> }
> }
> - return;
> + return ret;
> +}
> +
> +static void slave_read(void *opaque)
> +{
> + do_slave_read(opaque);
> }
>
> static int vhost_setup_slave_channel(struct vhost_dev *dev)
