linux-kernel - Re: [PATCH v7 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM

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Message-ID: <CACLfguVActMtC-_2fSS7GMWSgmSjaHFcXr-7H72Co301ZbXC6w@mail.gmail.com>
Date: Fri, 28 Mar 2025 13:47:30 +0800
From: Cindy Lu <lulu@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, mst@...hat.com, michael.christie@...cle.com, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v7 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM_OWNER

On Mon, Mar 3, 2025 at 5:12 PM Stefano Garzarella <sgarzare@...hat.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 <lulu@...hat.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 <lulu@...hat.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;
> >>         }
> >> +
>
> nit: this empyt line is not needed
>
sure , will fix this
Thanks
Cindy
> >> +#else
> >> +       if (ioctl == VHOST_FORK_FROM_OWNER) {
> >> +               /* When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is 'n', return error */
> >> +               r = -ENOTTY;
> >> +               goto done;
> >> +       }
> >> +#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'm not sure about this honestly, the user space has no way to figure
> out the default value and still has to do the IOCTL.
> So IMHO better to have a default value that is independent of the kernel
> configuration and consistent with the current behavior.
>
> Thanks,
> Stefano
>
> >
> >Other patches look good to me.
> >
> >Thanks
> >
> >>
> >
>