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Date: Fri, 17 Feb 2017 08:52:59 -0800 From: Andy Lutomirski <luto@...capital.net> To: Cyrill Gorcunov <gorcunov@...nvz.org> Cc: Linux FS Devel <linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...uxfoundation.org>, Andrew Vagin <avagin@...tuozzo.com>, Pavel Emelyanov <xemul@...tuozzo.com>, Michael Kerrisk <mtk.manpages@...il.com>, Kirill Kolyshkin <kir@...nvz.org>, Andrey Vagin <avagin@...nvz.org> Subject: Re: [RFC 1/2] fs,eventpoll: Add ability to install target file by its number On Fri, Feb 17, 2017 at 12:30 AM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote: > When we checkpoint a process we look into /proc/<pid>/fdinfo/<fd> of eventpoll > file and parse target files list from there. In most situations this is fine > because target file is present in the /proc/<pid>/fd/ list. But in case if file > descriptor was dup'ed or transferred via unix socket and closed after, > it might not be in the list and we can't figure out which file descriptor > to pass into epoll_ctl call. > > To resolve this tie lets add EPOLL_CTL_DUP operation which simply takes > target file descriptor number and installs it into a caller's file table, > thus we can use kcmp() syscall and figure out which exactly file to be > added into eventpoll on restore procedure. This is a scary thing to let an unprivileged process do. I'm wondering if there might be a nicer way to address this using a better interface in /proc.
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