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

Sage> I think this is the fundamental question: who do we give the
Sage> ammunition to, the user or app writer, or the sysadmin?

Sage> One might argue that we gave the user a similar power with
Sage> O_NOATIME (the power to break applications that assume atime is
Sage> accurate).  Here we give developers/users the power to not
Sage> update mtime and suffer the consequences (like, obviously,
Sage> breaking mtime-based backups).  It should be pretty obvious to
Sage> anyone using the flag what the consequences are.

Not modifying atime doesn't really break anything except people who
think they can tell when a file was last accessed.  Which isn't
critical (unless your in a paranoid security conscious place...) but
MTIME is another beast entirely.   Turning that off is going to break
lots of hidden assumptions.  

Sage> Note that we can suffer similar lapses in mtime with fdatasync
Sage> followed by a system crash.  And as Andy points out it's
Sage> semi-broken for writable mmap.  The crash case is obviously a
Sage> slightly different thing, but the idea that mtime can't always
Sage> be trusted certainly isn't crazy talk.

True, but after a crash... people expect and understand there might be
corruption in a filesystem.

Umm. No; people do not expect anything newer than ext3 to get
corrupted, ever.

In fact, I did not know about fdatasync/crash. That's rather nasty
surprise.

									Pavel
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