Subject: bug#33946: tail -f stops abruptly in AIX when piped.

From: "Ayappan P2" <[email-masked]>
Date: Tue, 15 Jan 2019 18:12:43 +0530

The patch/commit is not proper. The select() call will still be invoked in
AIX.
It should be like this.

# diff -u src/tail.c_orig src/tail.c
--- src/tail.c_orig     2019-01-01 19:39:32 +0000
+++ src/tail.c  2019-01-15 17:58:23 +0000
@@ -30,6 +30,9 @@
 #include <getopt.h>
 #include <sys/types.h>
 #include <signal.h>
+#ifdef _AIX
+# include <poll.h>
+#endif

 #include "system.h"
 #include "argmatch.h"
@@ -338,6 +341,15 @@
   if (! monitor_output)
     return;

+#ifdef _AIX
+  /* select on AIX was seen to give a readable event immediately.  */
+  struct pollfd pfd;
+  pfd.fd = STDOUT_FILENO;
+  pfd.events = POLLERR;
+
+   if (poll (&pfd, 1, 0) >= 0 && (pfd.revents & POLLERR))
+    raise (SIGPIPE);
+#else
   struct timeval delay;
   delay.tv_sec = delay.tv_usec = 0;

@@ -349,6 +361,7 @@
      and implies an error condition on output like broken pipe.  */
   if (select (STDOUT_FILENO + 1, &rfd, NULL, NULL, &delay) == 1)
     raise (SIGPIPE);
+#endif
 }

Thanks
Ayappan P

From:	Bernhard Voelker <[email-masked]>
To:	[email-masked], [email-masked], [email-masked]
Date:	01/15/2019 01:25 PM
Subject:	bug#33946: tail -f stops abruptly in AIX when piped.
Sent by:	"Bug-coreutils" <bug-coreutils-bounces
            +ayappap2=[email-masked]>

On 1/13/19 4:31 AM, Pádraig Brady wrote:
> Thanks for testing. Pushed at:
>
https://git.sv.gnu.org/gitweb/?p=coreutils.git;a=commitdiff;h=d5ab4cb

> -timeout 10 tail -f $mode $fastpoll out | sleep .1 || fail=1
> +(returns_ 124 timeout 10 tail -n2 -f $mode $fastpoll out && touch
timed_out) |
> + sed 2q > out2
> +test -e timed_out && fail=1
> +compare exp out2 || fail=1

I see the 'timed_out' file when running the test on openSUSE's build
service
for Linux x86_64, and can reproduce when running that in the local 'osc'
build
environment (chroot-based).

I'm not sure what's the problem though, but could this be related to
how we fixed 'tests/misc/seq-epipe.sh' a while ago in v8.25-42-g383e4b2ce?

BTW: in the 2nd iteration, the test doesn't delete 'timed_out',
so will always set fail=1 if the 1st one failed.

Have a nice day,
Berny