Re: [PATCH v4 1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs

Mike Rapoport
2021-03-23T08:27:47Z

On Mon, Mar 22, 2021 at 06:08:45PM -0400, Peter Xu wrote:
> UFFD_FEATURE_THREAD_ID is supported since Linux 4.14.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> man2/userfaultfd.2 | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index e7dc9f813..555e37409 100644
> --- a/man2/userfaultfd.2
> +++ b/man2/userfaultfd.2
> @@ -77,6 +77,13 @@ When the last file descriptor referring to a userfaultfd object is closed,
> all memory ranges that were registered with the object are unregistered
> and unread events are flushed.
> .\"
> +.PP
> +Since Linux 4.14, userfaultfd page fault message can selectively embed faulting
> +thread ID information into the fault message.
> +One needs to enable this feature explicitly using the
> +.BR UFFD_FEATURE_THREAD_ID
> +feature bit when initializing the userfaultfd context.
> +By default, thread ID reporting is diabled.

^ disabled :)
> .SS Usage
> The userfaultfd mechanism is designed to allow a thread in a multithreaded
> program to perform user-space paging for the other threads in the process.
> @@ -229,6 +236,9 @@ struct uffd_msg {
> struct {
> __u64 flags; /* Flags describing fault */
> __u64 address; /* Faulting address */
> + union {
> + __u32 ptid; /* Thread ID of the fault */
> + } feat;
> } pagefault;
>
> struct { /* Since Linux 4.11 */
> @@ -358,6 +368,9 @@ otherwise it is a read fault.
> .\" UFFD_PAGEFAULT_FLAG_WP is not yet supported.
> .RE
> .TP
> +.I pagefault.feat.pid
> +The thread ID that triggered the page fault.
> +.TP
> .I fork.ufd
> The file descriptor associated with the userfault object
> created for the child created by
> --
> 2.26.2
>

--
Sincerely yours,
Mike.