On Fri, Jun 2, 2017 at 10:18 PM, Arnd Bergmann [off-list ref] wrote:

On Fri, Jun 2, 2017 at 2:18 PM, Yan, Zheng [off-list ref] wrote:

quoted

On Fri, Jun 2, 2017 at 7:33 PM, Arnd Bergmann [off-list ref] wrote:

quoted

On Fri, Jun 2, 2017 at 1:18 PM, Yan, Zheng [off-list ref] wrote:
What I meant is another related problem in ceph_mkdir() where the
i_ctime field of the parent inode is different between the persistent
representation in the mds and the in-memory representation.

I don't see any problem in mkdir case. Parent inode's i_ctime in mds is set to
r_stamp. When client receives request reply, it set its in-memory inode's ctime
to the same time stamp.

Ok, I see it now, thanks for the clarification. Most other file systems do this
the other way round and update all fields in the in-memory inode structure
first and then write that to persistent storage, so I was getting confused about
the order of events here.

If I understand it all right, we have three different behaviors in ceph now,
though the differences are very minor and probably don't ever matter:

- in setattr(), we update ctime in the in-memory inode first and then send
  the same time to the mds, and expect to set it again when the reply comes.

- in ceph_write_iter write() and mmap/page_mkwrite(), we call
  file_update_time() to set i_mtime and i_ctime to the same
  timestamp first once a write is observed by the fs and then take
  two other timestamps that we send to the mds, and update the
  in-memory inode a second time when the reply comes. ctime
  is never older than mtime here, as far as I can tell, but it may
  be newer when the timer interrupt happens between taking the
  two stamps.

We don't use request to send i_mtime/i_ctime to mds in this case.
Instead, we use cap flush message. i_mtime/i_ctime are directly
encoded in cap flush message. When mds receives the cap flush message,
it writes i_mtime/i_ctime to persistent storage and sends a cap flush
ack message to client. (when client receives the cap flush ack
message, it does not update i_mtime/i_ctime). There is no issue as you
described.

- in all other calls, we only update the inode (and/or parent inode)
  after the reply arrives.

There are two cases. 1. Client updates in-memory inode's ctime, it
sends the new ctime to mds through cap flush message. 2. client set
mds request's r_stamp and send the request to mds. MDS updates
relavent inodes' ctime and sends reply to client. Client updates
in-memory inodes' ctime according to the reply.

Regards
Yan, Zheng

       Arnd

--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html