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Subject[RFC PATCH v2 0/3] realize dax_operations for dm-snapshot
From: Huaisheng Ye <>

Add NULL funtions for origin_dax_direct_access and
origin_dax_copy_from/to_iter in order to avoid building
error when CONFIG_DAX_DRIVER has NOT been enabled.


This series patches are used to realize the dax_operations for dm-snapshot
with persistent memory device.

Here are the steps about how to verify the function.

1. Configure the persistent memory to fs-dax mode and create namespace with ndctl;
2. find them in /dev;
# ndctl list
3. create lv_pmem (here is 4G size) for testing;
# pvcreate /dev/pmem0
# vgcreate vg_pmem /dev/pmem0
# lvcreate -L 4G -n lv_pmem vg_pmem
4. create filesystem (ext2 or ext4) to /dev/pmem0
# mkfs.ext2 -b 4096 /dev/vg_pmem/lv_pmem
5. mount pmem with DAX way;
# mkdir /mnt/lv_pmem
# mount -o dax /dev/vg_pmem/lv_pmem /mnt/lv_pmem/
6. cp some files to /mnt/lv_pmem;
# cp linear_table03.log /mnt/lv_pmem/
# cp test0.log /mnt/lv_pmem/
7. create snapshot for test (here I limit it to 1G size);
# lvcreate -L 1G -n snap_pmem -s /dev/vg_pmem/lv_pmem
8. modify the files copied with vim or copy more other new files;
# vim /mnt/lv_pmem/test0.log
9. umount the pmem device;
# umount /mnt/lv_pmem/
10.merge the snapshot back to origin;
# lvconvert --merge /dev/vg_pmem/snap_pmem
11.mount pmem device again for checking the content of files;
# mount -o dax /dev/vg_pmem/lv_pmem /mnt/lv_pmem/

Huaisheng Ye (3):
dm: enable dax_operations for dm-snapshot
dm: expand hc_map in mapped_device for lack of map
dm: expand valid types for dm-ioctl

drivers/md/dm-core.h | 1 +
drivers/md/dm-ioctl.c | 4 +++-
drivers/md/dm-snap.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++--
drivers/md/dm.c | 15 +++++++++++++++
4 files changed, 68 insertions(+), 3 deletions(-)


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