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 12:49:40 +0530
From:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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 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 ?. Is there a userspace
tool that use /proc/<pid>/mouninfo ?

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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