diff options
author | Kiyoshi Ueda <k-ueda@ct.jp.nec.com> | 2009-06-22 10:12:36 +0100 |
---|---|---|
committer | Alasdair G Kergon <agk@redhat.com> | 2009-06-22 10:12:36 +0100 |
commit | e6ee8c0b767540f59e20da3ced282601db8aa502 (patch) | |
tree | 101cb830994734eb45a4a47cd5988f24da67fa4f /lib/dma-debug.c | |
parent | cec47e3d4a861e1d942b3a580d0bbef2700d2bb2 (diff) |
dm: enable request based option
This patch enables request-based dm.
o Request-based dm and bio-based dm coexist, since there are
some target drivers which are more fitting to bio-based dm.
Also, there are other bio-based devices in the kernel
(e.g. md, loop).
Since bio-based device can't receive struct request,
there are some limitations on device stacking between
bio-based and request-based.
type of underlying device
bio-based request-based
----------------------------------------------
bio-based OK OK
request-based -- OK
The device type is recognized by the queue flag in the kernel,
so dm follows that.
o The type of a dm device is decided at the first table binding time.
Once the type of a dm device is decided, the type can't be changed.
o Mempool allocations are deferred to at the table loading time, since
mempools for request-based dm are different from those for bio-based
dm and needed mempool type is fixed by the type of table.
o Currently, request-based dm supports only tables that have a single
target. To support multiple targets, we need to support request
splitting or prevent bio/request from spanning multiple targets.
The former needs lots of changes in the block layer, and the latter
needs that all target drivers support merge() function.
Both will take a time.
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'lib/dma-debug.c')
0 files changed, 0 insertions, 0 deletions