From mboxrd@z Thu Jan 1 00:00:00 1970
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r@public.gmane.org
Subject: [Bug 79411] New: poll() fd negation trick doesn't work for fd 0
Date: Wed, 02 Jul 2014 13:19:39 +0000
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https://bugzilla.kernel.org/show_bug.cgi?id=79411
Bug ID: 79411
Summary: poll() fd negation trick doesn't work for fd 0
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: low
Priority: P1
Component: man-pages
Assignee: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
Reporter: nyh-TS7m/3hpY0sOpacJJkBjfT4kX+cae0hd@public.gmane.org
Regression: No
poll(2) contains the following paragraph:
The field fd contains a file descriptor for an open file. If this
field is negative, then the corresponding events field is ignored and
the revents field returns zero. (This provides an easy way of ignoring
a file descriptor for a single poll() call: simply negate the fd
field.)
The negation technique described here will work with one important assumption -
that fd 0 isn't one of the polled descriptors. This will normally be the case
(fd 0 will be stdin and not be polled), but it doesn't strictly have to be this
way. I think this needs to be pointed out. Perhaps say:
(This provides an easy way of ignoring a file descriptor for a single
poll() call: simply negate the fd field. This technique will not work if
one of the polled fd is 0).
Issue discovered by Avi Kivity.
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