[PATCH] docs: procs -- Describe /proc/<pid>/map_files entry

[Cyrill Gorcunov <gorcunov@openvz.org>]

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Kees Cook <keescook@chromium.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: "Kirill A. Shutemov" <kirill@shutemov.name>
CC: Calvin Owens <calvinowens@fb.com>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Oleg Nesterov <oleg@redhat.com>
CC: "Eric W. Biederman" <ebiederm@xmission.com>
CC: Al Viro <viro@zeniv.linux.org.uk>
CC: Peter Feiner <pfeiner@google.com>
CC: Pavel Emelyanov <xemul@openvz.org>
---

Gentlemen, could you please take a look once time permit.
Which questions this text raises so I could add more info
here (how we use it in criu, ptrace_may_access guards?)

 Documentation/filesystems/proc.txt |   23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

Index: linux-2.6.git/Documentation/filesystems/proc.txt
===================================================================
--- linux-2.6.git.orig/Documentation/filesystems/proc.txt
+++ linux-2.6.git/Documentation/filesystems/proc.txt
@@ -42,6 +42,7 @@ Table of Contents
   3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
   3.7   /proc/<pid>/task/<tid>/children - Information about task children
   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
+  3.9   /proc/<pid>/map_files - Information about memory mapped files
 
   4	Configuring procfs
   4.1	Mount options
@@ -1763,6 +1764,28 @@ pair provide additional information part
 	with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
 	still exhibits timer's remaining time.
 
+3.9	/proc/<pid>/map_files - Information about memory mapped files
+---------------------------------------------------------------------
+This directory consists of simbolic links which represent memory mapped files
+the process is carrying. A typical output is like the following
+
+     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
+     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
+     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
+     | ...
+     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
+     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
+
+The name of a link is virtual memory bounds a particular map exhibits, i.e.
+vm_area_struct::vm_start-vm_area_struct::vm_end.
+
+The main purpose of map_files directory is to be able to retrieve a set of
+memory mapped files in a fast way instead of parsing /proc/<pid>/maps or
+/proc/<pid>/smaps which contain a way more records. Same time one can open(2)
+mappings from the listings of two processes and comparing inodes figure out
+which anonymous memory areas are actually shared.
+
+
 ------------------------------------------------------------------------------
 Configuring procfs
 ------------------------------------------------------------------------------