Re: [PATCH 2/5] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs

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Hello Alex, and Peter,

Please take note below.

On 4/5/21 3:13 PM, Alejandro Colomar wrote:
> From: Peter Xu <peterx@xxxxxxxxxx>
> 
> UFFD_FEATURE_THREAD_ID is supported since Linux 4.14.
> 
> Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> [alx: srcfix]
> Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
> ---
>  man2/userfaultfd.2 | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index fa1b6514f..8245253c3 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
> +.B UFFD_FEATURE_THREAD_ID
> +feature bit when initializing the userfaultfd context.
> +By default, thread ID reporting is 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
 
Thanks. I've applied the patch, but I made a few tweaks afterwards,
as per the patch below. Notably, I changed "message" to
"notification", since that seems more consistent with the
language in the rest of the page. Is it okay, Peter?

Cheers,

Michael

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 8245253c3..eb2c6d5f9 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -78,8 +78,10 @@ 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.
+Since Linux 4.14,
+.\" commit 9d4ac934829ac58c5109c49e6dfe677300e5e652
+a userfaultfd page fault notification can selectively embed the
+faulting thread ID information in the notification.
 One needs to enable this feature explicitly using the
 .B UFFD_FEATURE_THREAD_ID
 feature bit when initializing the userfaultfd context.


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/



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