Commit 49d063cb authored by Andrey Vagin's avatar Andrey Vagin Committed by Linus Torvalds
Browse files

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: default avatarAndrey Vagin <avagin@openvz.org>
Acked-by: default avatarPavel Emelyanov <xemul@parallels.com>
Acked-by: default avatarCyrill 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f0b5664b

Documentation/filesystems/proc.txt

+12 −5
Original line number Diff line number Diff line
@@ -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

fs/proc/fd.c

+4 −2
Original line number Diff line number Diff line
@@ -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);

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