Re: [Qemu-devel] [PATCH] virtio-9p: add reset handler

[Stefan Hajnoczi]

On Thu, Oct 06, 2016 at 03:12:10PM +0200, Greg Kurz wrote:
> Virtio devices should implement the VirtIODevice->reset() function to
> perform necessary cleanup actions and to bring the device to a quiescent
> state.
> 
> In the case of the virtio-9p device, this means:
> - emptying the list of active PDUs (i.e. draining all in-flight I/O)
> - freeing all fids (i.e. close open file descriptors and free memory)
> 
> That's what this patch does.
> 
> The reset handler first waits for all active PDUs to complete. Since
> completion happens in the QEMU global aio context, we just have to
> loop around aio_poll() until the active list is empty.
> 
> The freeing part involves some actions to be performed on the backend,
> like closing file descriptors or flushing extended attributes to the
> underlying filesystem. The virtfs_reset() function already does the
> job: it calls free_fid() for all open fids not involved in an ongoing
> I/O operation. We are sure this is the case since we have drained
> the PDU active list.
> 
> The current code implements all backend accesses with coroutines, but we
> want to stay synchronous on the reset path. We can either change the
> current code to be able to run when not in coroutine context, or create
> a coroutine context and wait for virtfs_reset() to complete. This patch
> goes for the latter because it results in simpler code.
> 
> Note that we also need to create a dummy PDU because it is also an API
> to pass the FsContext pointer to all backend callbacks.
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>  hw/9pfs/9p.c               |   31 +++++++++++++++++++++++++++++++
>  hw/9pfs/9p.h               |    1 +
>  hw/9pfs/virtio-9p-device.c |    8 ++++++++
>  3 files changed, 40 insertions(+)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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