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I think the right approach here is to have the client set its own ctime so that it's locally useful but not to transmit it to the MDS. The MDS always uses its own clock to update the ctime/rctime. This means from the client's perspective that the ctime changes twice for a single metadata operation but I think that's acceptable. The standards provide no guarantees or guidance on this.

I totally disagree for the mtime case. This breaks rsync and lots of other applications expected behaviour. At least for mtime anyway. Ctime this is the sane behaviour.

mtime should be arbitrary. I've had issues with applications freak out when its in the future but it is technically 'valid'. But I've also encountered workloads where it gets set into the future so it gets left alone until after that date. (I work in HPC and scientists are odd sometimes). But the real issue is if I can't update mtime, rsync can't cheat and use mtimes to detect file changes. That makes many backups sad.

Anyway long story short, mtime should ALWAYS be whatever weird thing the client sets it to. Ctime is less important.

Thanks.

Yeah, we previously assigned mtimes from the MDS and it was a disaster. That's not something we'll be going back to!

I'm less sure about ctimes but I don't think applications outside of samba tend to care about those much...

see https://github.com/ceph/ceph/pull/32126. that commit add 'dirty_from' field to rstat, which is mds time. mds can use 'dirty_from' to decide if rctime should be set to a smaller value.

IMHO ctime should always be `ceph_clock_now()` rather than any time from the client.

Here's an XFS demo. Note how Change time is the clock when a change is made, not related to the arbitrary Modify time of the file:

# touch asdf
# stat asdf
  File: ‘asdf’
  Size: 0             Blocks: 0          IO Block: 4096   regular empty file
Device: fc01h/64513d    Inode: 25166519    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:user_tmp_t:s0
Access: 2020-10-15 14:33:51.874524960 +0200
Modify: 2020-10-15 14:33:51.874524960 +0200
Change: 2020-10-15 14:33:51.874524960 +0200
 Birth: -
# touch -t 202501010000 asdf 
# stat asdf
  File: ‘asdf’
  Size: 0             Blocks: 0          IO Block: 4096   regular empty file
Device: fc01h/64513d    Inode: 25166519    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Context: unconfined_u:object_r:user_tmp_t:s0
Access: 2025-01-01 00:00:00.000000000 +0100
Modify: 2025-01-01 00:00:00.000000000 +0100
Change: 2020-10-15 14:34:00.520475964 +0200
 Birth: -