On Tue, Mar 4, 2025 at 1:33 AM Michael S. Tsirkin <m...@redhat.com> wrote:
>
> On Mon, Mar 03, 2025 at 01:52:06PM +0800, Jason Wang wrote:
> > On Sun, Mar 2, 2025 at 10:34 PM Cindy Lu <l...@redhat.com> wrote:
> > >
> > > Introduce a new config knob `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL`,
> > > to control the availability of the `VHOST_FORK_FROM_OWNER` ioctl.
> > > When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set to n, the ioctl
> > > is disabled, and any attempt to use it will result in failure.
> > >
> > > Signed-off-by: Cindy Lu <l...@redhat.com>
> > > ---
> > > drivers/vhost/Kconfig | 15 +++++++++++++++
> > > drivers/vhost/vhost.c | 11 +++++++++++
> > > 2 files changed, 26 insertions(+)
> > >
> > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> > > index b455d9ab6f3d..e5b9dcbf31b6 100644
> > > --- a/drivers/vhost/Kconfig
> > > +++ b/drivers/vhost/Kconfig
> > > @@ -95,3 +95,18 @@ config VHOST_CROSS_ENDIAN_LEGACY
> > > If unsure, say "N".
> > >
> > > endif
> > > +
> > > +config VHOST_ENABLE_FORK_OWNER_IOCTL
> > > + bool "Enable IOCTL VHOST_FORK_FROM_OWNER"
> > > + default n
> > > + help
> > > + This option enables the IOCTL VHOST_FORK_FROM_OWNER, which
> > > allows
> > > + userspace applications to modify the thread mode for vhost
> > > devices.
> > > +
> > > + By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to
> > > `n`,
> > > + meaning the ioctl is disabled and any operation using this
> > > ioctl
> > > + will fail.
> > > + When the configuration is enabled (y), the ioctl becomes
> > > + available, allowing users to set the mode if needed.
> > > +
> > > + If unsure, say "N".
> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index fb0c7fb43f78..09e5e44dc516 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -2294,6 +2294,8 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned
> > > int ioctl, void __user *argp)
> > > r = vhost_dev_set_owner(d);
> > > goto done;
> > > }
> > > +
> > > +#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
> > > if (ioctl == VHOST_FORK_FROM_OWNER) {
> > > u8 inherit_owner;
> > > /*inherit_owner can only be modified before owner is set*/
> > > @@ -2313,6 +2315,15 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned
> > > int ioctl, void __user *argp)
> > > r = 0;
> > > goto done;
> > > }
> > > +
> > > +#else
> > > + if (ioctl == VHOST_FORK_FROM_OWNER) {
> > > + /* When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is 'n',
> > > return error */
> > > + r = -ENOTTY;
> > > + goto done;
> > > + }
>
> why do we need this? won't it fail as any other unsupported ioctl?
>
> > > +#endif
> > > +
> > > /* You must be the owner to do anything else */
> > > r = vhost_dev_check_owner(d);
> > > if (r)
> > > --
> > > 2.45.0
> >
> > Do we need to change the default value of the inhert_owner? For example:
> >
> > #ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
> > inherit_owner = false;
> > #else
> > inherit_onwer = true;
> > #endif
> >
> > ?
>
> I feel it is best to keep the default consistent.
Just want to make sure we are on the same page.
For "default", did you mean inherit_owner = false which is consistent
with behaviour without the vhost task?
Or inherit_onwer = true, then the new ioctl to make it false is
useless. And if legacy applications want kthread behaviour it needs to
be patched which seems self-contradictory.
> All the kconfig should do, is block the ioctl.
>
Thanks
>
> > Other patches look good to me.
> >
> > Thanks
> >
> > >
>
