On Mon, Feb 06, 2012 at 01:52:15PM +0000, Al Viro wrote:

On Mon, Feb 06, 2012 at 07:18:24AM -0500, Christoph Hellwig wrote:

quoted

On Mon, Feb 06, 2012 at 12:53:21PM +0100, David Sterba wrote:

quoted

On Sun, Feb 05, 2012 at 12:30:42PM +0200, Nikos Voutsinas wrote:

quoted

It's quite old, but what was this about;

http://thread.gmane.org/gmane.comp.file-systems.btrfs/4487

Thanks, the patch looks ok and works as expected.

Goffredo, do you want to resend it? (The lock around the mnt_root is not
necessary.) I think it's a -rc material, more people came to ask about
this on irc channel lately, we don't need to wait a full release cycle
to merge this fix.

No, it doesn't look good.  Please do not introduce anything touching
non-superblock fields in ->show_options, thanks.

Sorry, I'll be more carefull with vfs patches.

Umm...  seq_dentry() on root dentry (which is what's getting passed to
->show_options() now) would be OK; this kind of playing with ->d_name
is not.

Thanks for the suggestion. This should do it, 

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c

@@ -766,6 +766,9 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
                seq_puts(seq, ",inode_cache");
        if (btrfs_test_opt(root, SKIP_BALANCE))
                seq_puts(seq, ",skip_balance");
+       seq_puts(seq, ",subvol=");
+       seq_dentry(seq, vfs->mnt_root, " \t\n\\");
+
        return 0;
 }

( plus EXPORT_SYMBOL(seq_dentry) )

The 3rd argument (chars to be escaped in the path), is same as passed to other
seq_* funcs, though I'm not sure if we don't want to escape ',' as well, since
it may confuse option parsers out there. If the subvol= is kept as the last
one, then actual path is from '=' up to the first unescaped ' '.

If touching dentry name is forbidden, then we could entirely skip checking
whether it's '/', and always show subvol path. I don't see a problem from
user's/administrator's POV (and I'm not going to invent another way to check
for '/' by looking to other internal vfs items).

Full patch:

From: David Sterba <redacted>

Although it's not necessarily needed to show the mount option for the
toplevel subvolume, we cannot touch dentry name or other internal items
to check for it.

Signed-off-by: David Sterba <redacted>
---
 fs/btrfs/super.c |    6 ++++++
 fs/seq_file.c    |    1 +
 2 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 61717a4..dda5d6e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c

@@ -766,6 +766,12 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_puts(seq, ",inode_cache");
 	if (btrfs_test_opt(root, SKIP_BALANCE))
 		seq_puts(seq, ",skip_balance");
+	/*
+	 * Keep this one at the end
+	 */
+	seq_puts(seq, ",subvol=");
+	seq_dentry(seq, vfs->mnt_root, " \t\n\\");
+
 	return 0;
 }
 

diff --git a/fs/seq_file.c b/fs/seq_file.c
index dba43c3..ccbcc56 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c

@@ -498,6 +498,7 @@ int seq_dentry(struct seq_file *m, struct dentry *dentry, char *esc)
 
 	return res;
 }
+EXPORT_SYMBOL(seq_dentry);
 
 int seq_bitmap(struct seq_file *m, const unsigned long *bits,
 				   unsigned int nr_bits)

-- 
1.7.8