Re: [PATCH] man/man2/seccomp_unotify.2: Document SECCOMP_IOCTL_NOTIF_SET_FLAGS and SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP

[Alejandro Colomar <alx@kernel.org>]

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Hi,

On 2026-05-18T06:50:47+0100, funsafemath wrote:
> Document the SECCOMP_IOCTL_NOTIF_SET_FLAGS ioctl(2) operation and its only flag,
> SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP, which advises the scheduler to move the
> supervisor to the CPU on which the target process is executing for faster
> context switches.
> 
> <https://lore.kernel.org/r/20230308073201.3102738-5-avagin@google.com>
> 
> Signed-off-by: funsafemath <funsafemath@proton.me>

The patch looks mostly good.  See a minor comment below.


Have a lovely day!
Alex

> ---
>  man/man2/seccomp_unotify.2 | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/man/man2/seccomp_unotify.2 b/man/man2/seccomp_unotify.2
> index a5c1a4423..70b2996a9 100644
> --- a/man/man2/seccomp_unotify.2
> +++ b/man/man2/seccomp_unotify.2
> @@ -27,6 +27,7 @@ .SH SYNOPSIS
>  .BI "int ioctl(int " fd ", SECCOMP_IOCTL_NOTIF_ID_VALID, __u64 *" id );
>  .BI "int ioctl(int " fd ", SECCOMP_IOCTL_NOTIF_ADDFD,"
>  .BI "          struct seccomp_notif_addfd *" addfd );
> +.BI "int ioctl(int " fd ", SECCOMP_IOCTL_NOTIF_SET_FLAGS, unsigned long " flags );
>  .fi
>  .SH DESCRIPTION
>  This page describes the user-space notification mechanism provided by the
> @@ -881,6 +882,41 @@ .SS SECCOMP_IOCTL_NOTIF_ADDFD
>  ioctl(notifyFd, SECCOMP_IOCTL_NOTIF_SEND, resp);
>  .in
>  .EE
> +.\"
> +.SS SECCOMP_IOCTL_NOTIF_SET_FLAGS
> +The
> +.B SECCOMP_IOCTL_NOTIF_SET_FLAGS
> +operation (available since Linux 6.6)
> +\." commit 48a1084a8b7423642b5f17ca6202f6f277c5392b

Typo; you meant .\"
It's also repeated below.

Interestingly, this seems to also hide it as a comment, although
troff(1) prints a warning saying that something is wrong:

	alx@devuan:~/tmp$ cat comment.man 
	.TH comment 7 2026-05-18 experiments
	.SH Name
	comment \- trying different comments
	.SH Description
	Here goes one comment:
	.\" foo
	Comment ended.
	.P
	Here goes another comment?
	\." bar
	Comment ended.
	alx@devuan:~/tmp$ groff -Tutf8 -man -rCHECKSTYLE=3 -rLL=64n -ww comment.man 
	troff:comment.man:10: warning: name '"' not defined
	comment(7)      Miscellaneous Information Manual      comment(7)

	Name
	     comment - trying different comments

	Description
	     Here goes one comment: Comment ended.

	     Here goes another comment?  Comment ended.

	experiments                2026‐05‐18                 comment(7)

I'm curious about what happens in the roff(7) language for this to work
as a comment.

> +is used to modify the behavior of the seccomp user-space notification mechanism.
> +.P
> +The third
> +.BR ioctl (2)
> +argument,
> +.IR flags ,
> +is a bit mask that includes zero or more of the following flags:
> +.RS
> +.TP
> +.BR SECCOMP_USER_NOTIF_FD_SYNC_WAKE_UP " (since Linux 6.6)"
> +\." commit 48a1084a8b7423642b5f17ca6202f6f277c5392b
> +Advise the scheduler to move the supervisor to the current CPU.
> +.IP
> +In workflows where the target and supervisor wait for each other
> +(do not execute in parallel),
> +this flag makes the context switches a few times faster.
> +.RE
> +.P
> +On success,
> +this operation returns 0;
> +on failure, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +This operation can fail with the following errors:
> +.TP
> +.B EINVAL
> +An invalid value was specified in the
> +.I flags
> +argument.
>  .SH NOTES
>  One example use case for the user-space notification
>  mechanism is to allow a container manager
> -- 
> 2.52.0
> 



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

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