[PATCH] proc: show mnt_id in fdinfo files

[PATCH] proc: show mnt_id in fdinfo files

[Andrey Vagin]

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.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
 fs/proc/fd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 985ea88..0788d09 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);
-- 
1.8.5.3

Re: [PATCH] proc: show mnt_id in fdinfo files

[Pavel Emelyanov]

On 03/17/2014 02:39 PM, Andrey Vagin wrote:
> 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.
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Pavel Emelyanov <xemul@parallels.com>
> Signed-off-by: Andrey Vagin <avagin@openvz.org>

These IDs are already shown in the /proc/$pid/mountinfo, and for some FSs
can be obtained via path_to_handle_at(), so this patch just makes it work
for any FS and speeds things up.

Acked-by: Pavel Emelyanov <xemul@parallels.com>

> ---
>  fs/proc/fd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/proc/fd.c b/fs/proc/fd.c
> index 985ea88..0788d09 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);
> 

Re: [PATCH] proc: show mnt_id in fdinfo files

[Cyrill Gorcunov]

On Mon, Mar 17, 2014 at 03:30:26PM +0400, Pavel Emelyanov wrote:
> On 03/17/2014 02:39 PM, Andrey Vagin wrote:
> > 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.
> > 
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> > Cc: Pavel Emelyanov <xemul@parallels.com>
> > Signed-off-by: Andrey Vagin <avagin@openvz.org>
> 
> These IDs are already shown in the /proc/$pid/mountinfo, and for some FSs
> can be obtained via path_to_handle_at(), so this patch just makes it work
> for any FS and speeds things up.
> 
> Acked-by: Pavel Emelyanov <xemul@parallels.com>

I think Documentation/filesystems/proc.txt should be updated on top.
Other than that

Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>

Re: [PATCH] proc: show mnt_id in fdinfo files

[Andrew Morton]

On Mon, 17 Mar 2014 15:50:13 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:

> On Mon, Mar 17, 2014 at 03:30:26PM +0400, Pavel Emelyanov wrote:
> > On 03/17/2014 02:39 PM, Andrey Vagin wrote:
> > > 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.
> > > 
> > > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > > Cc: Oleg Nesterov <oleg@redhat.com>
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> > > Cc: Pavel Emelyanov <xemul@parallels.com>
> > > Signed-off-by: Andrey Vagin <avagin@openvz.org>
> > 
> > These IDs are already shown in the /proc/$pid/mountinfo, and for some FSs
> > can be obtained via path_to_handle_at(), so this patch just makes it work
> > for any FS and speeds things up.
> > 
> > Acked-by: Pavel Emelyanov <xemul@parallels.com>
> 
> I think Documentation/filesystems/proc.txt should be updated on top.

Yes please.

It would be nice to see example output in the changelog as well please.