On Tue, Jan 07, 2020 at 09:29:17AM -0800, Dan Williams wrote: > On Tue, Jan 7, 2020 at 9:08 AM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > > > On Tue, Jan 07, 2020 at 06:22:54AM -0800, Dan Williams wrote: > > > On Tue, Jan 7, 2020 at 4:52 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > > > > > On Mon, Dec 16, 2019 at 01:10:14PM -0500, Vivek Goyal wrote: > > > > > > Agree. In retrospect it was my laziness in the dax-device > > > > > > implementation to expect the block-device to be available. > > > > > > > > > > > > It looks like fs_dax_get_by_bdev() is an intercept point where a > > > > > > dax_device could be dynamically created to represent the subset range > > > > > > indicated by the block-device partition. That would open up more > > > > > > cleanup opportunities. > > > > > > > > > > Hi Dan, > > > > > > > > > > After a long time I got time to look at it again. Want to work on this > > > > > cleanup so that I can make progress with virtiofs DAX paches. > > > > > > > > > > I am not sure I understand the requirements fully. I see that right now > > > > > dax_device is created per device and all block partitions refer to it. If > > > > > we want to create one dax_device per partition, then it looks like this > > > > > will be structured more along the lines how block layer handles disk and > > > > > partitions. (One gendisk for disk and block_devices for partitions, > > > > > including partition 0). That probably means state belong to whole device > > > > > will be in common structure say dax_device_common, and per partition state > > > > > will be in dax_device and dax_device can carry a pointer to > > > > > dax_device_common. > > > > > > > > > > I am also not sure what does it mean to partition dax devices. How will > > > > > partitions be exported to user space. > > > > > > > > Dan, last time we talked you agreed that partitioned dax devices are > > > > rather pointless IIRC. Should we just deprecate partitions on DAX > > > > devices and then remove them after a cycle or two? > > > > > > That does seem a better plan than trying to force partition support > > > where it is not needed. > > > > Question: if one /did/ have a partitioned DAX device and used kpartx to > > create dm-linear devices for each partition, will DAX still work through > > that? > > The device-mapper support will continue, but it will be limited to > whole device sub-components. I.e. you could use kpartx to carve up > /dev/pmem0 and still have dax, but not partitions of /dev/pmem0. So we can't use fdisk/parted to partition /dev/pmem0. Given /dev/pmem0 is a block device, I thought tools will expect it to be partitioned. Sometimes I create those partitions and use /dev/pmem0. So what's the replacement for this. People often have tools/scripts which might want to partition the device and these will start failing. IOW, I do not understand that why being able to partition /dev/pmem0 (which is a block device from user space point of view), is pointless. Thanks Vivek
