Implement callout_drain_async(), inspired by the projects/hps_head

branch.

This function is used to drain a callout via a callback instead of
blocking the caller until the drain is complete. Refer to the
callout_drain_async() manual page for a detailed description.

Limitation: If a lock is used with the callout, the callout can only
be drained asynchronously one time unless the callout_init_mtx()
function is called again. This limitation is not present in
projects/hps_head and will require more invasive changes to the
timeout code, which was not in the scope of this patch.

Differential Revision:	https://reviews.freebsd.org/D3521
Reviewed by:		wblock
MFC after:		1 month

0 files changed, 0 insertions, 0 deletions