tree b43cc88d671e85840a625cdb0de75754182043ac
parent df5d2e9089c7d5b8c46f767e4278610ea3e815b9
author Alasdair G Kergon <agk@redhat.com> 1362177949 +0000
committer Alasdair G Kergon <agk@redhat.com> 1362177949 +0000

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>