2 files changed, 16 insertions, 7 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index f00bee144add..8b9cd8eb3f91 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -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
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 985ea881b5bc..0788d093f5d8 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -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);