dm: add bufio
The dm-bufio interface allows you to do cached I/O on devices,
holding recently-read blocks in memory and performing delayed writes.
We don't use buffer cache or page cache already present in the kernel, because:
* we need to handle block sizes larger than a page
* we can't allocate memory to perform reads or we'd have deadlocks
Currently, when a cache is required, we limit its size to a fraction of
available memory. Usage can be viewed and changed in
/sys/module/dm_bufio/parameters/ .
The first user is thin provisioning, but more dm users are planned.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index f75a66e..b1a9214 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -208,6 +208,14 @@
If unsure, say N.
+config DM_BUFIO
+ tristate
+ depends on BLK_DEV_DM && EXPERIMENTAL
+ ---help---
+ This interface allows you to do buffered I/O on a device and acts
+ as a cache, holding recently-read blocks in memory and performing
+ delayed writes.
+
config DM_CRYPT
tristate "Crypt target support"
depends on BLK_DEV_DM