On 28/07/2025 14:35, Ojaswin Mujoo wrote:
We guarantee that the write is committed all-or-nothing, but do rely on
userspace not issuing racing atomic writes or racing regular writes.
I can easily change this, as I mentioned, but I am not convinced that it is
a must.
Purely from a design point of view, I feel we are breaking atomicity and
hence we should serialize or just stop userspace from doing this (which
is a bit extreme).
If you check the man page description of RWF_ATOMIC, it does not mention
serialization. The user should conclude that usual direct IO rules
apply, i.e. userspace is responsible for serializing.
I know userspace should ideally not do overwriting atomic writes but if
it is something we are allowing (which we do) then it is
kernel's responsibility to ensure atomicity. Sure we can penalize them
by serializing the writes but not by tearing it.
With that reasoning, I don't think the test should accomodate for this
particular scenario.
I can send a patch to the community for xfs (to provide serialization),
like I showed earlier, to get opinion.
Thanks,
John
