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

[funsafemath <funsafemath@proton.me>]

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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>
---
 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
+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


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