On 08/16/2018 05:22 PM, John Ferlan wrote:
On 08/13/2018 06:49 AM, Michal Privoznik wrote:
Currently the way virStorageVolWipe() works is it looks up pool containing given volume and hold it locked throughout while API execution. This is suboptimal because wiping a volume means writing data to it which can take ages. And if the whole pool is locked during that operation no other API can be issued (nor pool-list).
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- src/storage/storage_backend_iscsi_direct.c | 5 +++++ src/storage/storage_backend_rbd.c | 7 ++++++- src/storage/storage_util.c | 8 +++++++- 3 files changed, 18 insertions(+), 2 deletions(-)
Why not be more similar to storageVolCreateXMLFrom? That is handle the in_use incr/decr at the storage driver level. Seems we could create a helper that would follow the same steps...
I'm not sure we can do that. Sure, I though of that but then I've seen virStorageBackendRBDVolWipe() which calls virStorageBackendRBDNewState() -> virStoragePoolObjGetDef() and we certainly do not want to call that with pool unlocked.
For volume wiping, RBD and iscsi-direct use the @pool (obj), but by incrementing not only vol->in_use, but the pool asyncjobs we can inhibit the undefine, destroy, or deletion of the pool that would cause issues for those uses AFAICT.
Ah, okay I haven't realized we do have asyncJobs. That way we can unlock the pool object just before calling the backend callback. However, for the RBD and iscsi-direct cases I think we still should guard PoolObjGetDef() calls with pool lock+unlock.
Inhibiting refresh during these operations is a matter of perhaps opinion as to whether it's a good idea or not - although I suppose if a volume is open for write (locked), trying to open/read to get stat type information probably is going to wait anyway (although I'll admit I haven't put much time or research into that thought - just going by gut feel ;-)).
Whether a good idea or not we should be prepared for that. But if we set asyncJob then refresh is denied, so we are safe IMO.
BTW: Wouldn't uploadVol have the same issues? Seems we have only cared about build vol from. Since uploadVol checks vol->in_use it seems logical using the same argument as above that it too should use some new helper to change pool asyncjobs and vol in_use. The building setting could just be another parameter.
Okay, I'll rework my patch. Michal