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 <gr...@kaod.org>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> hw/9pfs/9p.c | 31 +++++++++++++++++++++++++++++++
> hw/9pfs/9p.h | 1 +
> hw/9pfs/virtio-9p-device.c | 8 ++++++++
> 3 files changed, 40 insertions(+)
>
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 119ee584969b..42137395037e 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -3522,6 +3522,37 @@ void v9fs_device_unrealize_common(V9fsState *s, Error
> **errp)
> g_free(s->tag);
> }
>
> +
> +typedef struct VirtfsCoResetData {
> + V9fsPDU pdu;
> + bool done;
> +} VirtfsCoResetData;
> +
> +static void coroutine_fn virtfs_co_reset(void *opaque)
> +{
> + VirtfsCoResetData *data = opaque;
> +
> + virtfs_reset(&data->pdu);
> + data->done = true;
> +}
> +
> +void v9fs_reset(V9fsState *s)
> +{
> + VirtfsCoResetData data = { .pdu = { .s = s }, .done = false };
> + Coroutine *co;
> +
> + while (!QLIST_EMPTY(&s->active_list)) {
> + aio_poll(qemu_get_aio_context(), true);
> + }
> +
> + co = qemu_coroutine_create(virtfs_co_reset, &data);
> + qemu_coroutine_enter(co);
> +
> + while (!data.done) {
> + aio_poll(qemu_get_aio_context(), true);
> + }
> +}
> +
> static void __attribute__((__constructor__)) v9fs_set_fd_limit(void)
> {
> struct rlimit rlim;
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index d539d2ebe9c0..6b69eaf24614 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -339,5 +339,6 @@ ssize_t pdu_unmarshal(V9fsPDU *pdu, size_t offset, const
> char *fmt, ...);
> V9fsPDU *pdu_alloc(V9fsState *s);
> void pdu_free(V9fsPDU *pdu);
> void pdu_submit(V9fsPDU *pdu);
> +void v9fs_reset(V9fsState *s);
>
> #endif
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index 009b43f6d045..b73d72aceb64 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -130,6 +130,13 @@ static void virtio_9p_device_unrealize(DeviceState *dev,
> Error **errp)
> v9fs_device_unrealize_common(s, errp);
> }
>
> +static void virtio_9p_reset(VirtIODevice *vdev)
> +{
> + V9fsVirtioState *v = (V9fsVirtioState *)vdev;
> +
> + v9fs_reset(&v->state);
> +}
> +
> ssize_t virtio_pdu_vmarshal(V9fsPDU *pdu, size_t offset,
> const char *fmt, va_list ap)
> {
> @@ -188,6 +195,7 @@ static void virtio_9p_class_init(ObjectClass *klass, void
> *data)
> vdc->unrealize = virtio_9p_device_unrealize;
> vdc->get_features = virtio_9p_get_features;
> vdc->get_config = virtio_9p_get_config;
> + vdc->reset = virtio_9p_reset;
> }
>
> static const TypeInfo virtio_device_info = {
