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proc: show mnt_id in /proc/pid/fdinfo 

Currently we don't have a way how to determing from which mount point
file has been opened.  This information is required for proper dumping
and restoring file descriptos due to presence of mount namespaces.  It's
possible, that two file descriptors are opened using the same paths, but
one fd references mount point from one namespace while the other fd --
from other namespace.

$ ls -l /proc/1/fd/1
lrwx------ 1 root root 64 Mar 19 23:54 /proc/1/fd/1 -> /dev/null

$ cat /proc/1/fdinfo/1
pos:	0
flags:	0100002
mnt_id:	16

$ cat /proc/1/mountinfo | grep ^16
16 32 0:4 / /dev rw,nosuid shared:2 - devtmpfs devtmpfs rw,size=1013356k,nr_inodes=253339,mode=755

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Rob Landley <rob@landley.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Vagin 2014-04-07 15:38:34 -07:00 committed by Linus Torvalds
parent f0b5664ba7
commit 49d063cb35
2 changed files with 16 additions and 7 deletions
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17
Documentation/filesystems/proc.txt
View File

@ -1648,18 +1648,21 @@ pids, so one need to either stop or freeze processes being inspected
if precise results are needed.
3.7 /proc/<pid>/fdinfo/<fd> - Information about opened file
3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
---------------------------------------------------------------
This file provides information associated with an opened file. The regular
files have at least two fields -- 'pos' and 'flags'. The 'pos' represents
the current offset of the opened file in decimal form [see lseek(2) for
details] and 'flags' denotes the octal O_xxx mask the file has been
created with [see open(2) for details].
files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
represents the current offset of the opened file in decimal form [see lseek(2)
for details], 'flags' denotes the octal O_xxx mask the file has been
created with [see open(2) for details] and 'mnt_id' represents mount ID of
the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
for details].
A typical output is
pos: 0
flags: 0100002
mnt_id: 19
The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
pair provide additional information particular to the objects they represent.
@ -1668,6 +1671,7 @@ pair provide additional information particular to the objects they represent.
~~~~~~~~~~~~~
pos: 0
flags: 04002
mnt_id: 9
eventfd-count: 5a
where 'eventfd-count' is hex value of a counter.
@ -1676,6 +1680,7 @@ pair provide additional information particular to the objects they represent.
~~~~~~~~~~~~~~
pos: 0
flags: 04002
mnt_id: 9
sigmask: 0000000000000200
where 'sigmask' is hex value of the signal mask associated
@ -1685,6 +1690,7 @@ pair provide additional information particular to the objects they represent.
~~~~~~~~~~~
pos: 0
flags: 02
mnt_id: 9
tfd: 5 events: 1d data: ffffffffffffffff
where 'tfd' is a target file descriptor number in decimal form,
@ -1718,6 +1724,7 @@ pair provide additional information particular to the objects they represent.
pos: 0
flags: 02
mnt_id: 9
fanotify flags:10 event-flags:0
fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4

6
fs/proc/fd.c
View File

@ -11,6 +11,7 @@
#include <linux/proc_fs.h>
#include "../mount.h"
#include "internal.h"
#include "fd.h"
@ -48,8 +49,9 @@ static int seq_show(struct seq_file *m, void *v)
}
if (!ret) {
seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
(long long)file->f_pos, f_flags);
seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
(long long)file->f_pos, f_flags,
real_mount(file->f_path.mnt)->mnt_id);
if (file->f_op->show_fdinfo)
ret = file->f_op->show_fdinfo(m, file);
fput(file);