On Tue, Apr 3, 2018 at 12:39 PM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Tue, Apr 03 2018 at 2:24pm -0400, > Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > >> On Fri, Mar 30, 2018 at 9:03 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> > In preparation for allowing filesystems to augment the dev_pagemap >> > associated with a dax_device, add an ->fs_claim() callback. The >> > ->fs_claim() callback is leveraged by the device-mapper dax >> > implementation to iterate all member devices in the map and repeat the >> > claim operation across the array. >> > >> > In order to resolve collisions between filesystem operations and DMA to >> > DAX mapped pages we need a callback when DMA completes. With a callback >> > we can hold off filesystem operations while DMA is in-flight and then >> > resume those operations when the last put_page() occurs on a DMA page. >> > The ->fs_claim() operation arranges for this callback to be registered, >> > although that implementation is saved for a later patch. >> > >> > Cc: Alasdair Kergon <agk@xxxxxxxxxx> >> > Cc: Mike Snitzer <snitzer@xxxxxxxxxx> >> >> Mike, do these DM touches look ok to you? We need these ->fs_claim() >> / ->fs_release() interfaces for device-mapper to set up filesystem-dax >> infrastructure on all sub-devices whenever a dax-capable DM device is >> mounted. It builds on the device-mapper dax dependency removal >> patches. > > I'd prefer dm_dax_iterate() be renamed to dm_dax_iterate_devices() Ok, I'll fix that up. > But dm_dax_iterate() is weird... it is simply returning the struct > dax_device *dax_dev that is passed: seemingly without actually directly > changing anything about that dax_device (I can infer that you're > claiming the underlying devices, but...) I could at least add a note to see the comment in dm_dax_dev_claim(). The filesystem caller expects to get a dax_dev back or NULL from fs_dax_claim_bdev() if the claim failed. For fs_dax_claim() the return value could simply be bool for pass / fail, but I used dax_dev NULL / not-NULL instead. In the case of device-mapper the claim attempt can't fail for conflicting ownership reasons because the exclusive ownership of the underlying block device is already established by device-mapper before the fs claims the device-mapper dax device. > In general user's of ti->type->iterate_devices can get a result back > (via 'int' return).. you aren't using it that way (and maybe dax will > never have a need to return an answer). But all said, I think I'd > prefer to see dm_dax_iterate_devices() return void. > > But please let me know if I'm missing something, thanks. Oh, yeah, I like that better. I'll just make it return void and have dm_dax_fs_claim() return the dax_dev directly. Thanks Mike!
