Messages in this thread | | | Date | Sat, 26 Jan 2008 08:37:41 +0100 | From | "Michael Kerrisk" <> | Subject | Re: epoll and shared fd's |
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On Jan 25, 2008 12:57 AM, Davide Libenzi <davidel@xmailserver.org> wrote: > > On Thu, 24 Jan 2008, Pierre Habouzit wrote: > > > On Fri, Jan 18, 2008 at 09:10:18PM +0000, Davide Libenzi wrote: > > > On Fri, 18 Jan 2008, Pierre Habouzit wrote: > > > > > > > Hi, > > > > > > > > I just came across a strange behavior of epoll that seems to > > > > contradict the documentation. Here is what happens: > > > > > > > > * I have two processes P1 and P2, P1 accept()s connections, and send the > > > > resulting file descriptors to P2 through a unix socket. > > > > > > > > * P2 registers the received socket in his epollfd. > > > > > > > > [time passes] > > > > > > > > * P2 is done with the socket and closes it > > > > > > > > * P2 gets events for the socket again ! > > > > > > > > > > > > Though the documentation says that if a process closes a file > > > > descriptor, it gets unregistered. And yes I'm sure that P2 doens't dup() > > > > the file descriptor. Though (because of a bug) it was still open in > > > > P1[0], hence the referenced socket still live at the kernel level. > > > > > > > > Of course the userland workaround is to force the EPOLL_CTL_DEL before > > > > the close, which I now do, but costs me a syscall where I wanted to > > > > spare one :| > > > > > > For epoll, a close is when the kernel file* is released (that is, when all > > > its instances are gone). > > > We could put a special handling in filp_close(), but I don't think is a > > > good idea, and we're better live with the current behaviour. > > > > Okay, maybe updating the linux manpages to be more clear about that is > > the way to go then. Thanks > > Sure. I'll send Michael Kerrisk and updated statement for the A6 answer in > the epoll man page.
Thanks Davide -- yes please send me a patch.
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