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    Subject[PATCH 5.10 104/121] ceph: properly handle statfs on multifs setups
    Date
    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 f33bfb255db8f..08c8d34c98091 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


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