Merge tag 'ceph-for-6.6-rc1' of https://github.com/ceph/ceph-client

Pull ceph updates from Ilya Dryomov:
 "Mixed with some fixes and cleanups, this brings in reasonably complete
  fscrypt support to CephFS! The list of things which don't work with
  encryption should be fairly short, mostly around the edges: fallocate
  (not supported well in CephFS to begin with), copy_file_range
  (requires re-encryption), non-default striping patterns.

  This was a multi-year effort principally by Jeff Layton with
  assistance from Xiubo Li, Luís Henriques and others, including several
  dependant changes in the MDS, netfs helper library and fscrypt
  framework itself"

* tag 'ceph-for-6.6-rc1' of https://github.com/ceph/ceph-client: (53 commits)
  ceph: make num_fwd and num_retry to __u32
  ceph: make members in struct ceph_mds_request_args_ext a union
  rbd: use list_for_each_entry() helper
  libceph: do not include crypto/algapi.h
  ceph: switch ceph_lookup/atomic_open() to use new fscrypt helper
  ceph: fix updating i_truncate_pagecache_size for fscrypt
  ceph: wait for OSD requests' callbacks to finish when unmounting
  ceph: drop messages from MDS when unmounting
  ceph: update documentation regarding snapshot naming limitations
  ceph: prevent snapshot creation in encrypted locked directories
  ceph: add support for encrypted snapshot names
  ceph: invalidate pages when doing direct/sync writes
  ceph: plumb in decryption during reads
  ceph: add encryption support to writepage and writepages
  ceph: add read/modify/write to ceph_sync_write
  ceph: align data in pages in ceph_sync_write
  ceph: don't use special DIO path for encrypted inodes
  ceph: add truncate size handling support for fscrypt
  ceph: add object version support for sync read
  libceph: allow ceph_osdc_new_request to accept a multi-op read
  ...

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/filesystems/ceph.rst b/Documentation/filesystems/ceph.rst
index 76ce938e7024..085f309ece60 100644
--- a/Documentation/filesystems/ceph.rst
+++ b/Documentation/filesystems/ceph.rst
@@ -57,6 +57,16 @@ a snapshot on any subdirectory (and its nested contents) in the
 system.  Snapshot creation and deletion are as simple as 'mkdir
 .snap/foo' and 'rmdir .snap/foo'.
 
+Snapshot names have two limitations:
+
+* They can not start with an underscore ('_'), as these names are reserved
+  for internal usage by the MDS.
+* They can not exceed 240 characters in size.  This is because the MDS makes
+  use of long snapshot names internally, which follow the format:
+  `_<SNAPSHOT-NAME>_<INODE-NUMBER>`.  Since filenames in general can't have
+  more than 255 characters, and `<node-id>` takes 13 characters, the long
+  snapshot names can take as much as 255 - 1 - 1 - 13 = 240.
+
 Ceph also provides some recursive accounting on directories for nested
 files and bytes.  That is, a 'getfattr -d foo' on any directory in the
 system will reveal the total number of nested regular files and