[Bug 61911] New: incorrect sentence in the description of struct pollfd's events field

[Bug 61911] New: incorrect sentence in the description of struct pollfd's events field

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

https://bugzilla.kernel.org/show_bug.cgi?id=61911

            Bug ID: 61911
           Summary: incorrect sentence in the description of struct
                    pollfd's events field
           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: bonzini-mXXj517/zsQ@public.gmane.org
        Regression: No

The manual page says:

The field events is an input parameter, a bit mask specifying the events the
application is interested  in  for  the  file descriptor fd.  If this field is
specified as zero, then all events are ignored for fd and revents returns zero.


However, this is not what happens.  POLLHUP and POLLERR are always reported (as
one would expect, actually).

Test case 1:

#include <poll.h>
int main(void)
{
    struct pollfd pfd = { .fd = 0 };
    sleep(1);
    poll(&pfd, 1, 0);
}

$ echo x > fifo & strace -e poll ./a.out < fifo
poll([{fd=0, events=0}], 1, 0) = 1 ([{fd=0, revents=POLLHUP}])


Test case 2:

#include <poll.h>
int main(void)
{
    struct pollfd pfd = { .fd = 1 };
    sleep(1);
    poll(&pfd, 1, 0);
}


$ :< fifo & strace -e poll ./a.out > fifo
poll([{fd=1, events=0}], 1, 0) = 1 ([{fd=1, revents=POLLERR}])

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[Bug 61911] incorrect sentence in the description of struct pollfd's events field

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

https://bugzilla.kernel.org/show_bug.cgi?id=61911

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
         Resolution|---                         |CODE_FIX

--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Thanks, Paolo. I'm not sure what I was thinking of when I wrote that text. I
applied the patch below.

diff --git a/man2/poll.2 b/man2/poll.2
index b0159d2..0a70065 100644
--- a/man2/poll.2
+++ b/man2/poll.2
@@ -89,12 +89,15 @@ The field
 is an input parameter, a bit mask specifying the events the application
 is interested in for the file descriptor
 .IR fd .
-If this field is specified as zero,
-then all events are ignored for
-.IR fd
-and
+This field may be specified as zero,
+in which case the only events that can be returned in
 .I revents
-returns zero.
+are
+.BR POLLHUP ,
+.BR POLLERR ,
+and
+.B POLLNVAL
+(see below).

 The field
 .I revents

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