From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH] NFS support for btrfs - v2 Date: Mon, 18 Aug 2008 12:51:04 +0100 Message-ID: <1219060264.3184.366.camel@pmac.infradead.org> References: <200807210201.56690.balajirrao@gmail.com> <1218974002.3184.278.camel@pmac.infradead.org> <200808171821.43874.balajirrao@gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-btrfs@vger.kernel.org, Chris Mason To: Balaji Rao Return-path: In-Reply-To: <200808171821.43874.balajirrao@gmail.com> List-ID: On Sun, 2008-08-17 at 18:21 +0530, Balaji Rao wrote: > > Note that the first problem you'll hit is the lack of stable fsid -- > > because btrfs uses an anonymous superblock, it might cause stale file > > handles after a reboot, unless your test setup mounts exactly the same > > anonymous file systems each time. That bit me when I context switched > > from something else and had debugfs mounted before btrfs, then rebooted > > and didn't mount debugfs first. I'll deal with the fsid problem > > separately; just be aware of it and avoid it for now. > > > Hmmm.. how do we deal with that ? First we teach nfs-utils to derive a UUID from the 'f_fsid' field it's already being given by the kernel when it calls statfs(): git.infradead.org/users/dwmw2/nfs-utils.git Then we make btrfs put something suitable into the f_fsid field in btrfs_statfs(). The patch below works OK, but doesn't yet handle subvolumes -- it gives the same fsid for all subvolumes. But then, since we're also returning the same {dev,ino#} for all subvolumes, nfs exporting isn't the _only_ thing that's going to get confused... From: David Woodhouse Date: Mon, 18 Aug 2008 12:01:52 +0100 Subject: [PATCH] Fill f_fsid field in btrfs_statfs() Signed-off-by: David Woodhouse --- super.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/super.c b/super.c index e830e0e..6446ab7 100644 --- a/super.c +++ b/super.c @@ -489,6 +489,7 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) struct btrfs_root *root = btrfs_sb(dentry->d_sb); struct btrfs_super_block *disk_super = &root->fs_info->super_copy; int bits = dentry->d_sb->s_blocksize_bits; + __be32 *fsid = (__be32 *)root->fs_info->fsid; buf->f_namelen = BTRFS_NAME_LEN; buf->f_blocks = btrfs_super_total_bytes(disk_super) >> bits; @@ -497,6 +498,11 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf) buf->f_bavail = buf->f_bfree; buf->f_bsize = dentry->d_sb->s_blocksize; buf->f_type = BTRFS_SUPER_MAGIC; + /* We treat it as constant endianness (it doesn't matter _which_) + because we want the fsid to come out the same whether mounted + on a big-endian or little-endian host */ + buf->f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]); + buf->f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]); return 0; } -- 1.5.5.1 -- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation