Hello everyone,
I am very glad to introduce my work dm-snap-mv here.
what is dm-snap-mv
-------------------
The dm-snap-mv is a target module for device-mapper, which can take
multiple snapshots against an existing block device(origin device).
All snapshots are saved in an independent block device(COW device).
The copy-on-write is used, so only diff-data will be saved in the COW device.
features
--------
1. snapshot of origin
2. snapshot of snapshot
3. instant snapshot creation and deletion
4. origin and snapshots are concurrent readable/writable
5. rollback snapshot to origin
6. multiple origin devices share a COW device
7. multiple COW devices are supported
diagram
-------
+---------------------+ +---------------+ +--------------+
read <--| |----- | | |
| origin dm_dev | | origin_dev | COW | |
write ---| |----> |-----> snapshot-1 |
+---------------------+ +--|------------+ | ... |
| | ... |
+---------------------+ +--|------------------+ ... |
read <--| |-------?- snapshot-N |
| snapshot-X dm_dev | | cow_dev |
write ---| |----> |
+---------------------+ +------------------------------------+
dm_dev: device-mapper device, created by "dmsetup create ..."
COW: copy-on-write
download the source
-----------------------
http://github.com/mcpacino/dm-snap-mv
git clone git://github.com/mcpacino/dm-snap-mv.git
a kernel patch
--------------
Now, dm-snap-mv highly depends on a kernel patch below, which make __getblk()
can get a 4K buffer head while block size of the disk is NOT 4K.
Signed-off-by: Cong Meng <mcpacino@xxxxxxxxx>
---
fs/buffer.c | 7 ++-----
1 files changed, 2 insertions(+), 5 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 3e7dca2..f7f9d33 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1051,10 +1051,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
pgoff_t index;
int sizebits;
- sizebits = -1;
- do {
- sizebits++;
- } while ((size << sizebits) < PAGE_SIZE);
+ sizebits = PAGE_CACHE_SHIFT - bdev->bd_inode->i_blkbits;
index = block >> sizebits;
@@ -2924,7 +2921,7 @@ int submit_bh(int rw, struct buffer_head * bh)
*/
bio = bio_alloc(GFP_NOIO, 1);
- bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
+ bio->bi_sector = bh->b_blocknr << (bh->b_bdev->bd_inode->i_blkbits - 9);
bio->bi_bdev = bh->b_bdev;
bio->bi_io_vec[0].bv_page = bh->b_page;
bio->bi_io_vec[0].bv_len = bh->b_size;
--
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