Always use an overlapped structure when calling DeviceIoControl

This change fixes deadlocks occurring when communicating with the WNBD driver using DeviceIoControl[1][2].

We're setting FILE_FLAG_OVERLAPPED when opening the WNBD device in order to be able to submit multiple requests simultaneously. The Windows docs state that in this case, an OVERLAPED structure must be passed to functions such as ReadFile or WriteFile without explicitly mentioning DeviceIoControl.

Apparently DeviceIoControl can hang if we don't pass an overlapped structure, especially when having a high number of concurrent requests. This is likely related to the event wait involved.

We're going to update the libwnbd Ioctl functions, adding an optional LPOVERLAPPED argument. When not provided by the caller, we're initalizing an internal OVERLAPED structure and wait for the operation on the behalf of the caller, mimicking the Windows behavior.

We're trying to re-use overlapped structures and events as much as possible, especially in the IO path. The IO dispatch loop will reuse the same events but we can't do much about "WnbdSendResponse" since that will be called by libwnbd consumers from arbitrary threads. We're adding "WnbdSendResponseEx" though, letting the caller provide an overlapped structure.

Another advantage of adding overlapped parameters is that we allow libwnbd consumers to perform any Ioctl call asynchronously.

[1] profiler counters: http://paste.openstack.org/raw/797772/ [2] wnbd / ceph counters: http://paste.openstack.org/raw/799072/

Signed-off-by: Lucian Petrut lpetrut@cloudbasesolutions.com

cloudbase / wnbd

Always use an overlapped structure when calling DeviceIoControl #30