Re: [patch v4 resend 1/2] procfs: fdinfo -- Extend information about epoll target files
From: Andrei Vagin <hidden>
Date: 2017-05-09 17:48:11
Also in:
linux-fsdevel, lkml
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 <redacted>
Acked-by: Andrei Vagin <redacted>
quoted hunk ↗ jump to hunk
CC: Al Viro <viro@zeniv.linux.org.uk> CC: Andrew Morton <redacted> CC: Andrey Vagin <redacted> CC: Pavel Emelyanov <redacted> CC: Michael Kerrisk <redacted> 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 followingIndex: 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; }