On Thu, Feb 13, 2020 at 3:29 PM Ira Weiny <ira.weiny@xxxxxxxxx> wrote: > > On Thu, Feb 13, 2020 at 11:58:39AM -0800, Darrick J. Wong wrote: > > On Thu, Feb 13, 2020 at 11:05:13AM -0800, Ira Weiny wrote: > > > On Thu, Feb 13, 2020 at 11:01:57AM -0800, 'Ira Weiny' wrote: > > > > On Wed, Feb 12, 2020 at 02:49:48PM -0500, Jeff Moyer wrote: > > > > > Ira Weiny <ira.weiny@xxxxxxxxx> writes: > > > > > > > > > > > [snip] > > > > > > > > Given that we document the dax mount > > > > > option as "the way to get dax," it may be a good idea to allow for a > > > > > user to selectively disable dax, even when -o dax is specified. Is that > > > > > possible? > > > > > > > > Not with this patch set. And I'm not sure how that would work. The idea was > > > > that -o dax was simply an override for users who were used to having their > > > > entire FS be dax. We wanted to depreciate the use of "-o dax" in general. The > > > > individual settings are saved so I don't think it makes sense to ignore the -o > > > > dax in favor of those settings. Basically that would IMO make the -o dax > > > > useless. > > > > > > Oh and I forgot to mention that setting 'dax' on the root of the FS basically > > > provides '-o dax' functionality by default with the ability to "turn it off" > > > for files. > > > > Please don't further confuse FS_XFLAG_DAX and S_DAX. > > Yes... the above text is wrong WRT statx. But setting the physical > XFS_DIFLAG2_DAX flag on the root directory will by default cause all files and > directories created there to be XFS_DIFLAG2_DAX and so forth on down the tree > unless explicitly changed. This will be the same as mounting with '-o dax' but > with the ability to turn off dax for individual files. Which I think is the > functionality Jeff is wanting. To be clear you mean turn off XFS_DIFLAG2_DAX, not mask S_DAX when you say "turn off dax", right? The mount option simply forces "S_DAX" on all regular files as long as the underlying device (or soon to be superblock for virtiofs) supports it. There is no method to mask S_DAX when the filesystem was mounted with -o dax. Otherwise we would seem to need yet another physical flag to "always disable" dax.
