[PATCH AUTOSEL 5.15 6/7] ceph: properly handle statfs on multifs setups

Sasha Levin
2021-11-26T02:32:39Z

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit 8cfc0c7ed34f7929ce7e5d7c6eecf4d01ba89a84 ]

ceph_statfs currently stuffs the cluster fsid into the f_fsid field.
This was fine when we only had a single filesystem per cluster, but now
that we have multiples we need to use something that will vary between
them.

Change ceph_statfs to xor each 32-bit chunk of the fsid (aka cluster id)
into the lower bits of the statfs->f_fsid. Change the lower bits to hold
the fscid (filesystem ID within the cluster).

That should give us a value that is guaranteed to be unique between
filesystems within a cluster, and should minimize the chance of
collisions between mounts of different clusters.

URL: https://tracker.ceph.com/issues/52812
Reported-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ceph/super.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index fd8742bae8471..202ddde3d62ad 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -52,8 +52,7 @@ static int ceph_statfs(struct dentry *dentry, struct kstatfs *buf)
struct ceph_fs_client *fsc = ceph_inode_to_client(d_inode(dentry));
struct ceph_mon_client *monc = &fsc->client->monc;
struct ceph_statfs st;
- u64 fsid;
- int err;
+ int i, err;
u64 data_pool;

if (fsc->mdsc->mdsmap->m_num_data_pg_pools == 1) {
@@ -99,12 +98,14 @@ static int ceph_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_namelen = NAME_MAX;

/* Must convert the fsid, for consistent values across arches */
+ buf->f_fsid.val[0] = 0;
mutex_lock(&monc->mutex);
- fsid = le64_to_cpu(*(__le64 *)(&monc->monmap->fsid)) ^
- le64_to_cpu(*((__le64 *)&monc->monmap->fsid + 1));
+ for (i = 0 ; i < sizeof(monc->monmap->fsid) / sizeof(__le32) ; ++i)
+ buf->f_fsid.val[0] ^= le32_to_cpu(((__le32 *)&monc->monmap->fsid)[i]);
mutex_unlock(&monc->mutex);

- buf->f_fsid = u64_to_fsid(fsid);
+ /* fold the fs_cluster_id into the upper bits */
+ buf->f_fsid.val[1] = monc->fs_cluster_id;

return 0;
}
--
2.33.0