[Bug 137351] New: MSG_NOSIGNAL not documented

[Bug 137351] New: MSG_NOSIGNAL not documented

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=137351

            Bug ID: 137351
           Summary: MSG_NOSIGNAL not documented
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: man-pages
          Assignee: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
          Reporter: ivan.kharpalev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
        Regression: No

MSG_NOSIGNAL is not documented in man 2 recv.

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[Bug 137351] MSG_NOSIGNAL not documented in man 2 recv, OR misprint in man recvmsg in the line "This can be avoided by passing the MSG_NOSIGNAL flag to sendmsg(2) or recvmsg(2)."

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=137351

Ivan Kharpalev <ivan.kharpalev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|MSG_NOSIGNAL not documented |MSG_NOSIGNAL not documented
                   |                            |in man 2 recv, OR misprint
                   |                            |in man recvmsg in the line
                   |                            |"This can be avoided by
                   |                            |passing the MSG_NOSIGNAL
                   |                            |flag to sendmsg(2) or
                   |                            |recvmsg(2)."

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[Bug 137351] MSG_NOSIGNAL not documented in man 2 recv, OR misprint in man recvmsg in the line "This can be avoided by passing the MSG_NOSIGNAL flag to sendmsg(2) or recvmsg(2)."

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=137351

Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
But, as far as I know, it does nothing for recv(2). If you believe otherwise,
please add some supporting info.

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[PATCH] unix.7: Explain that MSG_NOSIGNAL is useless for recvmsg(2)

[Laurent Georget]

recvmsg(2) never causes a "Broken pipe" error but the unix(7) man page implies
that MSG_NOSIGNAL can be used in the flags of recvmsg(2) to avoid sending a
SIGPIPE. Fixes Bug 137351.

Signed-Off-By: Laurent Georget <laurent.georget-vbcOdlJ0SulGWvitb5QawA@public.gmane.org>

---
 man7/unix.7 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Hi Michael,

I found the culprit line in unix(7). It can be misleading indeed because it
that it makes sense to use MSG_NOSIGNAL as a flag to recvmsg(2) to avoid a
SIGPIPE but recvmsg(2) actually never triggers such an error. I propose the
patch below to fix this.

Best regards,

Laurent Georget

diff --git a/man7/unix.7 b/man7/unix.7
index 82715f9..fce5eb2 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -515,12 +515,12 @@ Remote socket was closed on a stream socket.
 If enabled, a
 .B SIGPIPE
 is sent as well.
-This can be avoided by passing the
+Sending the signal can be avoided by passing the
 .B MSG_NOSIGNAL
 flag to
 .BR sendmsg (2)
-or
-.BR recvmsg (2).
+.RB ( recvmsg (2)
+never causes such an error).
 .TP
 .B EPROTONOSUPPORT
 Passed protocol is not
-- 
2.9.0

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[Bug 137351] MSG_NOSIGNAL not documented in man 2 recv, OR misprint in man recvmsg in the line "This can be avoided by passing the MSG_NOSIGNAL flag to sendmsg(2) or recvmsg(2)."

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=137351

--- Comment #2 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
I see that you changed the title of the bug. This is far too cryptic as a way
of reporting a bug. I can't find the text you refer to. Please note in a
comment exactly the text and exactly the page you are referring to, and also
check that the bug is present in the latest man page.

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Re: [PATCH] unix.7: Explain that MSG_NOSIGNAL is useless for recvmsg(2)

[Michael Kerrisk (man-pages)]

Hello Laurent,

On 07/22/2016 08:45 AM, Laurent Georget wrote:
> recvmsg(2) never causes a "Broken pipe" error but the unix(7) man page implies
> that MSG_NOSIGNAL can be used in the flags of recvmsg(2) to avoid sending a
> SIGPIPE. Fixes Bug 137351.
>
> Signed-Off-By: Laurent Georget <laurent.georget-vbcOdlJ0SulGWvitb5QawA@public.gmane.org>
>
> ---
>  man7/unix.7 | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> Hi Michael,
>
> I found the culprit line in unix(7). It can be misleading indeed because it
> that it makes sense to use MSG_NOSIGNAL as a flag to recvmsg(2) to avoid a
> SIGPIPE but recvmsg(2) actually never triggers such an error. I propose the
> patch below to fix this.

Thanks for delving into this and finding the page that had the problem
reported in https://bugzilla.kernel.org/show_bug.cgi?id=137351

I applied a slightly somewhat different patch. See below.

> Best regards,
>
> Laurent Georget
>
> diff --git a/man7/unix.7 b/man7/unix.7
> index 82715f9..fce5eb2 100644
> --- a/man7/unix.7
> +++ b/man7/unix.7
> @@ -515,12 +515,12 @@ Remote socket was closed on a stream socket.
>  If enabled, a
>  .B SIGPIPE
>  is sent as well.
> -This can be avoided by passing the
> +Sending the signal can be avoided by passing the
>  .B MSG_NOSIGNAL
>  flag to
>  .BR sendmsg (2)
> -or
> -.BR recvmsg (2).
> +.RB ( recvmsg (2)
> +never causes such an error).

I think the parenthetical comment isn't needed. The previous page text was
obviously wrong, but we don't need to mention recvmsg() in the fix.

>  .TP
>  .B EPROTONOSUPPORT
>  Passed protocol is not


I applied this patch:

[[
diff --git a/man7/unix.7 b/man7/unix.7
index e111734..0d44dd6 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -518,9 +518,9 @@ is sent as well.
  This can be avoided by passing the
  .B MSG_NOSIGNAL
  flag to
-.BR sendmsg (2)
+.BR send (2)
  or
-.BR recvmsg (2).
+.BR sendmsg (2).
  .TP
  .B EPROTONOSUPPORT
  Passed protocol is not
]]

Cheers,

Michael

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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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[Bug 137351] MSG_NOSIGNAL not documented in man 2 recv, OR misprint in man recvmsg in the line "This can be avoided by passing the MSG_NOSIGNAL flag to sendmsg(2) or recvmsg(2)."

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=137351

Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |CODE_FIX

--- Comment #3 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Applied the patch below. Closing this bug...

diff --git a/man7/unix.7 b/man7/unix.7
index e111734..0d44dd6 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -518,9 +518,9 @@ is sent as well.
 This can be avoided by passing the
 .B MSG_NOSIGNAL
 flag to
-.BR sendmsg (2)
+.BR send (2)
 or
-.BR recvmsg (2).
+.BR sendmsg (2).
 .TP
 .B EPROTONOSUPPORT
 Passed protocol is not

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