On Tue, Sep 21, 2021 at 07:16:26PM -0700, Dan Williams wrote: > On Tue, Sep 21, 2021 at 1:32 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > On Tue, Sep 21, 2021 at 10:44:31AM +1000, Dave Chinner wrote: > > > I think this wants to be a behavioural modifier for existing > > > operations rather than an operation unto itself. i.e. similar to how > > > KEEP_SIZE modifies ALLOC behaviour but doesn't fundamentally alter > > > the guarantees ALLOC provides userspace. > > > > > > In this case, the change of behaviour over ZERO_RANGE is that we > > > want physical zeros to be written instead of the filesystem > > > optimising away the physical zeros by manipulating the layout > > > of the file. > > > > Yes. > > > > > Then we have and API that looks like: > > > > > > ALLOC - allocate space efficiently > > > ALLOC | INIT - allocate space by writing zeros to it > > > ZERO - zero data and preallocate space efficiently > > > ZERO | INIT - zero range by writing zeros to it > > > > > > Which seems to cater for all the cases I know of where physically > > > writing zeros instead of allocating unwritten extents is the > > > preferred behaviour of fallocate().... > > > > Agreed. I'm not sure INIT is really the right name, but I can't come > > up with a better idea offhand. > > FUA? As in, this is a forced-unit-access zeroing all the way to media > bypassing any mechanisms to emulate zero-filled payloads on future > reads. FALLOC_FL_ZERO_EXISTING, because you want to zero the storage that already exists at that file range? --D
