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

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 <redacted>

---
 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.

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

-- 
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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