Re: [PATCH RFC] vfs: add a O_NOMTIME flag

quoted

quoted

The criteria for using O_NOMTIME is the same as for using O_NOATIME:
owning the file or having the CAP_FOWNER capability.  If we're not
comfortable allowing owners to prevent mtime/ctime updates then we
should add a tunable to allow O_NOMTIME.  Maybe a mount option?

I dislike "turn off safety for performance" options because Joe
SpeedRacer will always select performance over safety.

Well, for ceph there's no safety concern.  They never use cmtime in
these files.

So are you suggesting not implementing this and making them rework their
IO paths to avoid the fs maintaining mtime so that we don't give Joe
Speedracer more rope?  Or are we talking about adding some speed bumps
that ceph can flip on that might give Joe Speedracer pause?

Maybe one way to make it less of an attractive nuisance would be to hide
it under open_by_handle_at().  Like xfs_open_by_handle() does today but
we probably don't want to unconditionally add it to the generic path so
we'd have a flag.

They want to move to opening by handles anyway to avoid dirent lookups
when opening cold files.

- z