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SubjectRe: [patch v4 resend 1/2] procfs: fdinfo -- Extend information about epoll target files
On Mon, Apr 24, 2017 at 06:39:27PM +0300, Cyrill Gorcunov wrote:
> Since it is possbile to have same number in tfd field (say
> file added, closed, then nother file dup'ed to same number
> and added back) it is imposible to distinguish such target
> files solely by their numbers.
>
> Strictly speaking regular applications don't need to recognize
> these targets at all but for checkpoint/restore sake we need
> to collect targets to be able to push them back on restore
> stage in a proper order.
>
> Thus lets add file position, inode and device number where
> this target lays. This three fields can be used as a primary
> key for sorting, and together with kcmp help CRIU can find
> out an exact file target (from the whole set of processes
> being checkpointed).
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

Acked-by: Andrei Vagin <avagin@virtuozzo.com>

> CC: Al Viro <viro@zeniv.linux.org.uk>
> CC: Andrew Morton <akpm@linuxfoundation.org>
> CC: Andrey Vagin <avagin@openvz.org>
> 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>
> ---
> Documentation/filesystems/proc.txt | 6 +++++-
> fs/eventpoll.c | 8 ++++++--
> 2 files changed, 11 insertions(+), 3 deletions(-)
>
> Index: linux-ml.git/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux-ml.git.orig/Documentation/filesystems/proc.txt
> +++ linux-ml.git/Documentation/filesystems/proc.txt
> @@ -1779,12 +1779,16 @@ pair provide additional information part
> pos: 0
> flags: 02
> mnt_id: 9
> - tfd: 5 events: 1d data: ffffffffffffffff
> + tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
>
> where 'tfd' is a target file descriptor number in decimal form,
> 'events' is events mask being watched and the 'data' is data
> associated with a target [see epoll(7) for more details].
>
> + The 'pos' is current offset of the target file in decimal form
> + [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
> + where target file resides, all in hex format.
> +
> Fsnotify files
> ~~~~~~~~~~~~~~
> For inotify files the format is the following
> Index: linux-ml.git/fs/eventpoll.c
> ===================================================================
> --- linux-ml.git.orig/fs/eventpoll.c
> +++ linux-ml.git/fs/eventpoll.c
> @@ -883,10 +883,14 @@ static void ep_show_fdinfo(struct seq_fi
> mutex_lock(&ep->mtx);
> for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {
> struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
> + struct inode *inode = file_inode(epi->ffd.file);
>
> - seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",
> + seq_printf(m, "tfd: %8d events: %8x data: %16llx "
> + " pos:%lli ino:%lx sdev:%x\n",
> epi->ffd.fd, epi->event.events,
> - (long long)epi->event.data);
> + (long long)epi->event.data,
> + (long long)epi->ffd.file->f_pos,
> + inode->i_ino, inode->i_sb->s_dev);
> if (seq_has_overflowed(m))
> break;
> }
>

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