linux-kernel - Re: [PATCH v8 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM

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Message-ID: <CACLfguX7FJXdMi7CGxyDR+CtkHdgQOXm7T4fO6hBsFJ0Wa-2WA@mail.gmail.com>
Date: Thu, 3 Apr 2025 13:49:06 +0800
From: Cindy Lu <lulu@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: 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 v8 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM_OWNER

On Tue, Apr 1, 2025 at 9:21 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Fri, Mar 28, 2025 at 06:02:52PM +0800, Cindy Lu 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 |  3 +++
> > 2 files changed, 18 insertions(+)
>
> IMHO this patch should be squashed with "[PATCH v8 6/8] vhost: uapi to
> control task mode (owner vs kthread)".
>
> It might break the bisection to support an ioctl, and after a few
> commits enable or disable it depending on a kernel configuration.
>
> >
> >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
>
> nit: there is a mix of tabs and spaces in the next block, should we
> fix it?
>
sure ,will fix this
Thanks
Cindy
> >+
> >+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.
>    ^
>    tabs
>
> >+
> >+          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.
>    ^
>    spaces
> >+
> >+        If unsure, say "N".
>    ^
>    tabs
>
will fix this
Thanks
Cindy
> >diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >index fb0c7fb43f78..568e43cb54a9 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 +2315,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> >               r = 0;
> >               goto done;
> >       }
> >+#endif
> >       /* You must be the owner to do anything else */
> >       r = vhost_dev_check_owner(d);
> >       if (r)
> >--
> >2.45.0
> >
>