ceph: quota: add initial infrastructure to support cephfs quotas

This patch adds the infrastructure required to support cephfs quotas as it
is currently implemented in the ceph fuse client.  Cephfs quotas can be
set on any directory, and can restrict the number of bytes or the number
of files stored beneath that point in the directory hierarchy.

Quotas are set using the extended attributes 'ceph.quota.max_files' and
'ceph.quota.max_bytes', and can be removed by setting these attributes to
'0'.

Link: http://tracker.ceph.com/issues/22372
Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph.txt
index 0b302a11718a..094772481263 100644
--- a/Documentation/filesystems/ceph.txt
+++ b/Documentation/filesystems/ceph.txt
@@ -62,6 +62,18 @@ subdirectories, and a summation of all nested file sizes.  This makes
 the identification of large disk space consumers relatively quick, as
 no 'du' or similar recursive scan of the file system is required.
 
+Finally, Ceph also allows quotas to be set on any directory in the system.
+The quota can restrict the number of bytes or the number of files stored
+beneath that point in the directory hierarchy.  Quotas can be set using
+extended attributes 'ceph.quota.max_files' and 'ceph.quota.max_bytes', eg:
+
+ setfattr -n ceph.quota.max_bytes -v 100000000 /some/dir
+ getfattr -n ceph.quota.max_bytes /some/dir
+
+A limitation of the current quotas implementation is that it relies on the
+cooperation of the client mounting the file system to stop writers when a
+limit is reached.  A modified or adversarial client cannot be prevented
+from writing as much data as it needs.
 
 Mount Syntax
 ============