linux-kernel - Re: [PATCH -V16 10/12] vfs: Export file system uuid via /proc/<pid>mountinfo

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Date:	Mon, 12 Jul 2010 10:27:52 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	miklos@...redi.hu, linux-fsdevel@...r.kernel.org,
	sfrench@...ibm.com, philippe.deniel@....FR,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	viro@...iv.linux.org.uk, adilger@....com, corbet@....net,
	neilb@...e.de, npiggin@...e.de, hooanon05@...oo.co.jp,
	bfields@...ldses.org
Subject: Re: [PATCH -V16 10/12] vfs: Export file system uuid via /proc/<pid>mountinfo

On Mon, 12 Jul 2010, Aneesh Kumar K. V wrote:
> On Mon, 12 Jul 2010 12:05:43 +0530, "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> > We add a per superblock uuid field. File systems should
> > update the uuid in the fill_super callback
> > 
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> > ---
> >  fs/namespace.c     |    3 +++
> >  include/linux/fs.h |    1 +
> >  2 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/fs/namespace.c b/fs/namespace.c
> > index 88058de..5dbdbd6 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -871,6 +871,9 @@ static int show_mountinfo(struct seq_file *m, void *v)
> >  	if (IS_MNT_UNBINDABLE(mnt))
> >  		seq_puts(m, " unbindable");
> > 
> > +	/* print the uuid */
> > +	seq_printf(m, " uuid:%pU", mnt->mnt_sb->s_uuid);
> > +
> >  	/* Filesystem specific data */
> >  	seq_puts(m, " - ");
> >  	show_type(m, sb);
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 3103c39..5f43472 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1367,6 +1367,7 @@ struct super_block {
> >  	wait_queue_head_t	s_wait_unfrozen;
> > 
> >  	char s_id[32];				/* Informational name */
> > +	u8 s_uuid[16];				/* UUID */
> > 
> >  	void 			*s_fs_info;	/* Filesystem private info */
> >  	fmode_t			s_mode;
> 
> since it is an optional tag is it ok to do the below patch ? or does
> optional is a way to introduce changes across kernel version  and
> each line is suppose to have new added fields ?.

Tagged fields are optional, so yes, the patch is OK.

>  Is there a userspace
> tool that use /proc/<pid>/mouninfo ?

libmount from recent enough util-linux is using mountinfo.  So
mount(8) should be using it, as well as some other utilities in
util-linux.

Thanks,
Miklos

> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 5dbdbd6..7542959 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -833,6 +833,16 @@ const struct seq_operations mounts_op = {
>  	.show	= show_vfsmnt
>  };
>  
> +static int uuid_is_nil(u8 *uuid)
> +{
> +	int i;
> +	u8  *cp = (u8 *)uuid;
> +
> +	for (i = 0; i < 16; i++)
> +		if (*cp++) return 0;	/* not nil */
> +	return 1;	/* is nil */
> +}
> +
>  static int show_mountinfo(struct seq_file *m, void *v)
>  {
>  	struct proc_mounts *p = m->private;
> @@ -871,8 +881,9 @@ static int show_mountinfo(struct seq_file *m, void *v)
>  	if (IS_MNT_UNBINDABLE(mnt))
>  		seq_puts(m, " unbindable");
>  
> +	if (!uuid_is_nil(mnt->mnt_sb->s_uuid))
>  	/* print the uuid */
> -	seq_printf(m, " uuid:%pU", mnt->mnt_sb->s_uuid);
> +		seq_printf(m, " uuid:%pU", mnt->mnt_sb->s_uuid);
>  
>  	/* Filesystem specific data */
>  	seq_puts(m, " - ");
> 
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