path: root/include
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authorAlasdair G Kergon <agk@redhat.com>2013-03-01 22:45:49 +0000
committerAlasdair G Kergon <agk@redhat.com>2013-03-01 22:45:49 +0000
commitb0d8ed4d96a26ef3ac54a4aa8911c9413070662e (patch)
treeb43cc88d671e85840a625cdb0de75754182043ac /include
parentdf5d2e9089c7d5b8c46f767e4278610ea3e815b9 (diff)
dm: add target num_write_bios fn
Add a num_write_bios function to struct target. If an instance of a target sets this, it will be queried before the target's mapping function is called on a write bio, and the response controls the number of copies of the write bio that the target will receive. This provides a convenient way for a target to send the same data to more than one device. The new cache target uses this in writethrough mode, to send the data both to the cache and the backing device. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'include')
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index d5f984b0746..1e483fa7afb 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -175,6 +175,14 @@ struct target_type {
#define DM_TARGET_IMMUTABLE 0x00000004
#define dm_target_is_immutable(type) ((type)->features & DM_TARGET_IMMUTABLE)
+ * Some targets need to be sent the same WRITE bio severals times so
+ * that they can send copies of it to different devices. This function
+ * examines any supplied bio and returns the number of copies of it the
+ * target requires.
+ */
+typedef unsigned (*dm_num_write_bios_fn) (struct dm_target *ti, struct bio *bio);
struct dm_target {
struct dm_table *table;
struct target_type *type;
@@ -214,6 +222,13 @@ struct dm_target {
unsigned per_bio_data_size;
+ /*
+ * If defined, this function is called to find out how many
+ * duplicate bios should be sent to the target when writing
+ * data.
+ */
+ dm_num_write_bios_fn num_write_bios;
/* target specific data */
void *private;