This is a support for DAX in btrfs. I understand there have been previous attempts at it. However, I wanted to make sure copy-on-write (COW) works on dax as well.
Before I present this to the FS folks I wanted to run this through the btrfs. Even though I wish, I cannot get it correct the first time around :/.. Here are some questions for which I need suggestions: Questions: 1. I have been unable to do checksumming for DAX devices. While checksumming can be done for reads and writes, it is a problem when mmap is involved because btrfs kernel module does not get back control after an mmap() writes. Any ideas are appreciated, or we would have to set nodatasum when dax is enabled. 2. Currently, a user can continue writing on "old" extents of an mmaped file after a snapshot has been created. How can we enforce writes to be directed to new extents after snapshots have been created? Do we keep a list of all mmap()s, and re-mmap them after a snapshot? Tested by creating a pmem device in RAM with "memmap=2G!4G" kernel command line parameter. [PATCH 01/10] btrfs: create a mount option for dax [PATCH 02/10] btrfs: basic dax read [PATCH 03/10] btrfs: dax: read zeros from holes [PATCH 04/10] Rename __endio_write_update_ordered() to [PATCH 05/10] btrfs: Carve out btrfs_get_extent_map_write() out of [PATCH 06/10] btrfs: dax write support [PATCH 07/10] dax: export functions for use with btrfs [PATCH 08/10] btrfs: dax add read mmap path [PATCH 09/10] btrfs: dax support for cow_page/mmap_private and shared [PATCH 10/10] btrfs: dax mmap write fs/btrfs/Makefile | 1 fs/btrfs/ctree.h | 17 ++ fs/btrfs/dax.c | 303 ++++++++++++++++++++++++++++++++++++++++++++++++++-- fs/btrfs/file.c | 29 ++++ fs/btrfs/inode.c | 54 +++++---- fs/btrfs/ioctl.c | 5 fs/btrfs/super.c | 15 ++ fs/dax.c | 35 ++++-- include/linux/dax.h | 16 ++ 9 files changed, 430 insertions(+), 45 deletions(-) -- Goldwyn
