Revision 0791e3644e5ef21646fe565b9061788d05ec71d4 authored by Cyrill Gorcunov on 12 July 2017, 21:34:28 UTC, committed by Linus Torvalds on 12 July 2017, 23:26:01 UTC
With current epoll architecture target files are addressed with
file_struct and file descriptor number, where the last is not unique.
Moreover files can be transferred from another process via unix socket,
added into queue and closed then so we won't find this descriptor in the
task fdinfo list.

Thus to checkpoint and restore such processes CRIU needs to find out
where exactly the target file is present to add it into epoll queue.
For this sake one can use kcmp call where some particular target file
from the queue is compared with arbitrary file passed as an argument.

Because epoll target files can have same file descriptor number but
different file_struct a caller should explicitly specify the offset
within.

To test if some particular file is matching entry inside epoll one have
to

 - fill kcmp_epoll_slot structure with epoll file descriptor,
   target file number and target file offset (in case if only
   one target is present then it should be 0)

 - call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot)
    - the kernel fetch file pointer matching file descriptor @fd of pid1
    - lookups for file struct in epoll queue of pid2 and returns traditional
      0,1,2 result for sorting purpose

Link: http://lkml.kernel.org/r/20170424154423.511592110@gmail.com
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 77493f0
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Aaron Durbin <adurbin@google.com>
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Adrian Bunk <bunk@stusta.de>
Adriana Reus <adi.reus@gmail.com> <adriana.reus@intel.com>
Alan Cox <alan@lxorguk.ukuu.org.uk>
Alan Cox <root@hraefn.swansea.linux.org.uk>
Aleksey Gorelov <aleksey_gorelov@phoenix.com>
Al Viro <viro@ftp.linux.org.uk>
Al Viro <viro@zenIV.linux.org.uk>
Andreas Herrmann <aherrman@de.ibm.com>
Andrey Ryabinin <ryabinin.a.a@gmail.com> <a.ryabinin@samsung.com>
Andrew Morton <akpm@linux-foundation.org>
Andrew Vasquez <andrew.vasquez@qlogic.com>
Andy Adamson <andros@citi.umich.edu>
Antoine Tenart <antoine.tenart@free-electrons.com>
Antonio Ospite <ao2@ao2.it> <ao2@amarulasolutions.com>
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Arnaud Patard <arnaud.patard@rtp-net.org>
Arnd Bergmann <arnd@arndb.de>
Axel Dyks <xl@xlsigned.net>
Axel Lin <axel.lin@gmail.com>
Ben Gardner <bgardner@wabtec.com>
Ben M Cahill <ben.m.cahill@intel.com>
Björn Steinbrink <B.Steinbrink@gmx.de>
Boris Brezillon <boris.brezillon@free-electrons.com>
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Brian Avery <b.avery@hp.com>
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Damian Hobson-Garcia <dhobsong@igel.co.jp>
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Frank Rowand <frowand.list@gmail.com> <frowand@mvista.com>
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Henk Vergonet <Henk.Vergonet@gmail.com>
Henrik Kretzschmar <henne@nachtwindheim.de>
Henrik Rydberg <rydberg@bitmath.org>
Herbert Xu <herbert@gondor.apana.org.au>
Jacob Shin <Jacob.Shin@amd.com>
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James E Wilson <wilson@specifix.com>
James Ketrenos <jketreno@io.(none)>
Javi Merino <javi.merino@kernel.org> <javi.merino@arm.com>
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Jeff Garzik <jgarzik@pretzel.yyz.us>
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Johan Hovold <johan@kernel.org> <jhovold@gmail.com>
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Koushik <raghavendra.koushik@neterion.com>
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Mauro Carvalho Chehab <mchehab@kernel.org> <m.chehab@samsung.com>
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