On Fri, 28 Oct 2022 at 06:55, Jason Wang <jasow...@redhat.com> wrote:
>
> From: Si-Wei Liu <si-wei....@oracle.com>
>
> Similar to other vhost backends, vhostfd can be passed to vhost-vdpa
> backend as another parameter to instantiate vhost-vdpa net client.
> This would benefit the use case where only open file descriptors, as
> opposed to raw vhost-vdpa device paths, are accessible from the QEMU
> process.
>
> (qemu) netdev_add type=vhost-vdpa,vhostfd=61,id=vhost-vdpa1
>
> @@ -634,14 +634,29 @@ int net_init_vhost_vdpa(const Netdev *netdev, const
> char *name,
>
> assert(netdev->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> opts = &netdev->u.vhost_vdpa;
> - if (!opts->vhostdev) {
> - error_setg(errp, "vdpa character device not specified with
> vhostdev");
> + if (!opts->has_vhostdev && !opts->has_vhostfd) {
> + error_setg(errp,
> + "vhost-vdpa: neither vhostdev= nor vhostfd= was
> specified");
> return -1;
> }
>
> - vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR, errp);
> - if (vdpa_device_fd == -1) {
> - return -errno;
> + if (opts->has_vhostdev && opts->has_vhostfd) {
> + error_setg(errp,
> + "vhost-vdpa: vhostdev= and vhostfd= are mutually
> exclusive");
> + return -1;
> + }
> +
> + if (opts->has_vhostdev) {
> + vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR, errp);
> + if (vdpa_device_fd == -1) {
> + return -errno;
> + }
> + } else if (opts->has_vhostfd) {
> + vdpa_device_fd = monitor_fd_param(monitor_cur(), opts->vhostfd,
> errp);
> + if (vdpa_device_fd == -1) {
> + error_prepend(errp, "vhost-vdpa: unable to parse vhostfd: ");
> + return -1;
> + }
> }
Hi; this doesn't compile with clang:
../../net/vhost-vdpa.c:654:16: error: variable 'vdpa_device_fd' is
used uninitialized whenever 'if' condition is false
[-Werror,-Wsometimes-uninitialized]
} else if (opts->has_vhostfd) {
^~~~~~~~~~~~~~~~~
../../net/vhost-vdpa.c:662:33: note: uninitialized use occurs here
r = vhost_vdpa_get_features(vdpa_device_fd, &features, errp);
^~~~~~~~~~~~~~
../../net/vhost-vdpa.c:654:12: note: remove the 'if' if its condition
is always true
} else if (opts->has_vhostfd) {
^~~~~~~~~~~~~~~~~~~~~~~
../../net/vhost-vdpa.c:629:23: note: initialize the variable
'vdpa_device_fd' to silence this warning
int vdpa_device_fd;
^
= 0
1 error generated.
(clang version 10.0.0-4ubuntu1).
It's a false positive -- the compiler doesn't manage to figure out
that the error checks further up mean that there's no code path where
vdpa_device_fd isn't initialized. Put another way, the problem is
that we check "if (opts->has_vhostfd)" when in fact that condition
must always be true.
We could fix this by for instance:
diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 854ebd61ae6..b1572ea00bc 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -634,11 +634,6 @@ int net_init_vhost_vdpa(const Netdev *netdev,
const char *name,
assert(netdev->type == NET_CLIENT_DRIVER_VHOST_VDPA);
opts = &netdev->u.vhost_vdpa;
- if (!opts->has_vhostdev && !opts->has_vhostfd) {
- error_setg(errp,
- "vhost-vdpa: neither vhostdev= nor vhostfd= was specified");
- return -1;
- }
if (opts->has_vhostdev && opts->has_vhostfd) {
error_setg(errp,
@@ -657,6 +652,10 @@ int net_init_vhost_vdpa(const Netdev *netdev,
const char *name,
error_prepend(errp, "vhost-vdpa: unable to parse vhostfd: ");
return -1;
}
+ } else {
+ error_setg(errp,
+ "vhost-vdpa: neither vhostdev= nor vhostfd= was specified");
+ return -1;
}
r = vhost_vdpa_get_features(vdpa_device_fd, &features, errp);
or alternatively by
diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 854ebd61ae6..e370ecb8ebd 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -651,7 +651,8 @@ int net_init_vhost_vdpa(const Netdev *netdev,
const char *name,
if (vdpa_device_fd == -1) {
return -errno;
}
- } else if (opts->has_vhostfd) {
+ } else {
+ /* has_vhostfd */
vdpa_device_fd = monitor_fd_param(monitor_cur(), opts->vhostfd, errp);
if (vdpa_device_fd == -1) {
error_prepend(errp, "vhost-vdpa: unable to parse vhostfd: ");
I think I prefer the second of these.
(I'll post a patch properly in a moment I guess.)
-- PMM
