Re: [PATCH v1 09/10] man/man2/statmount.2: Document req.mnt_ns_fd

Alejandro Colomar <[email protected]> Wed, 11 Feb 2026 15:01:10 +0100

Newsgroups	dev.linux.lists.criu,org.kernel.vger.linux-man
Message-ID	<aYyLe7m6A47F0cc2@devuan>

On 2026-02-10T02:47:42+0530, Bhavik Sachdev wrote:
> Document the new mnt_ns_fd parameter to struct mnt_id_req.
> 
> req.mnt_ns_fd can be used to query for a mount in a foreign mount
> namespace.
> 
> The mnt_ns_fd parameter description is based on this commit message [1].
> 
> Link [1]:
> <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9020d0d844ad58a051f90b1e5b82ba34123925b9>
> 
> Signed-off-by: Bhavik Sachdev <[email protected]>
> ---
>  man/man2/statmount.2 | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/man/man2/statmount.2 b/man/man2/statmount.2
> index 0b906a334..e835eb0f6 100644
> --- a/man/man2/statmount.2
> +++ b/man/man2/statmount.2
> @@ -24,6 +24,7 @@ .SH SYNOPSIS
>  .EX
>  .B struct mnt_id_req {
>  .BR "    __u32  size;" "        /* sizeof(struct mnt_id_req) */"
> +.BR "    __u32  mnt_ns_fd;" "   /* fd of mnt_ns to query the mnt_id in */"
>  .BR "    __u64  mnt_id;" "      /* The mnt_id being queried */"
>  .BR "    __u64  param;" "       /* An ORed combination of the STATMOUNT_ constants */"
>  .BR "    __u32  mnt_ns_id;" "   /* The id of mnt_ns to query the mnt_id in */"
> @@ -74,7 +75,9 @@ .SH DESCRIPTION
>  To access a mount's status,
>  the caller must have CAP_SYS_ADMIN in the user namespace.
>  In case of accessing a mount in a foreign mount namespace (specified via
> -.IR req.mnt_ns_id ),
> +.I req.mnt_ns_id
> +or
> +.IR req.mnt_ns_fd ),
>  the foreign mount namespace should be child of the current namespace.
>  .P
>  This function returns information about a mount,
> @@ -97,6 +100,15 @@ .SS The mnt_id_req structure
>  it should always be set to
>  .IR sizeof(struct\~mnt_id_req) .
>  .P
> +.I req.mnt_ns_fd
> +can be obtained from
> +.B PIDFD_GET_MNT_NAMESPACE
> +.BR ioctl (2)
> +operation or by opening a file descriptor to
> +.IR /proc/[pid]/ns/mnt

Reformat:

	.IR /proc/ pid /ns/mnt


Cheers,
Alex

> +and is used to specify a foreign mount namespace in which to query
> +.IR req.mnt_id .
> +.P
>  .I req.mnt_id
>  can be obtained from either
>  .BR statx (2)
> @@ -365,6 +377,13 @@ .SH ERRORS
>  .I req
>  is of insufficient size to be utilized.
>  .TP
> +.B EINVAL
> +Both
> +.I req.mnt_ns_id
> +and
> +.I req.mnt_ns_fd
> +were set.
> +.TP
>  .B E2BIG
>  .I req
>  is too large.
> -- 
> 2.53.0
> 
> 

-- 
<https://www.alejandro-colomar.es>

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