Messages in this thread | | | Date | Tue, 27 Jan 2015 22:43:11 +0200 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] docs: procs -- Describe /proc/<pid>/map_files entry |
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On Tue, Jan 27, 2015 at 11:50:49AM -0800, Kees Cook wrote: > On Tue, Jan 27, 2015 at 1:41 AM, Cyrill Gorcunov <gorcunov@openvz.org> wrote: > > 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. > > Thanks for details! I still don't understand how this is used for > checkpoint/restore when the mmap offset isn't shown. Can't a process > map, say 4K of a file, from different offsets, and it would show up > as: > > 400000-401000 -> /some/file > 401000-402000 -> /some/file > > but there'd be no way to know how to restore that mapping?
IIUC, it's complementry to data in maps/smap. If the file was closed and unlinked, it's the only way to get file descriptor which points the inode under mapping.
-- Kirill A. Shutemov
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