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SubjectRe: [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ
On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote:
> On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote:
>> Add a new vq, cmdq, to handle requests between the device and driver.
>>
>> This patch implements two commands sent from the device and handled in
>> the driver.
>> 1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report
>> the guest memory statistics to the host. The stats_vq mechanism is not
>> used when the cmdq mechanism is enabled.
>> 2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to
>> report the guest unused pages to the host.
>>
>> Since now we have a vq to handle multiple commands, we need to keep only
>> one vq operation at a time. Here, we change the existing START_USE()
>> and END_USE() to lock on each vq operation.
>>
>> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
>> Signed-off-by: Liang Li <liang.z.li@intel.com>
>> ---
>> drivers/virtio/virtio_balloon.c | 245 ++++++++++++++++++++++++++++++++++--
>> drivers/virtio/virtio_ring.c | 25 +++-
>> include/linux/virtio.h | 2 +
>> include/uapi/linux/virtio_balloon.h | 10 ++
>> 4 files changed, 265 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
>> index aa4e7ec..ae91fbf 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt;
>>
>> struct virtio_balloon {
>> struct virtio_device *vdev;
>> - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
>> + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq;
>>
>> /* The balloon servicing is delegated to a freezable workqueue. */
>> struct work_struct update_balloon_stats_work;
>> struct work_struct update_balloon_size_work;
>> + struct work_struct cmdq_handle_work;
>>
>> /* Prevent updating balloon when it is being canceled. */
>> spinlock_t stop_update_lock;
>> @@ -90,6 +91,12 @@ struct virtio_balloon {
>> /* Memory statistics */
>> struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
>>
>> + /* Cmdq msg buffer for memory statistics */
>> + struct virtio_balloon_cmdq_hdr cmdq_stats_hdr;
>> +
>> + /* Cmdq msg buffer for reporting ununsed pages */
>> + struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr;
>> +
>> /* To register callback in oom notifier call chain */
>> struct notifier_block nb;
>> };
>> @@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work)
>> queue_work(system_freezable_wq, work);
>> }
>>
>> +static unsigned int cmdq_hdr_add(struct virtqueue *vq,
>> + struct virtio_balloon_cmdq_hdr *hdr,
>> + bool in)
>> +{
>> + unsigned int id = VIRTQUEUE_DESC_ID_INIT;
>> + uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr);
>> +
>> + virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in);
>> +
>> + /* Deliver the hdr for the host to send commands. */
>> + if (in) {
>> + hdr->flags = 0;
>> + virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL);
>> + virtqueue_kick(vq);
>> + }
>> +
>> + return id;
>> +}
>> +
>> +static void cmdq_add_chain_desc(struct virtio_balloon *vb,
>> + struct virtio_balloon_cmdq_hdr *hdr,
>> + uint64_t addr,
>> + uint32_t len,
>> + unsigned int *head_id,
>> + unsigned int *prev_id)
>> +{
>> +retry:
>> + if (*head_id == VIRTQUEUE_DESC_ID_INIT) {
>> + *head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0);
>> + *prev_id = *head_id;
>> + }
>> +
>> + virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0);
>> + if (*head_id == *prev_id) {
> That's an ugly way to detect ring full.

It's actually not detecting ring full. I will call it tail_id, instead
of prev_id.
So, *head_id == *tail_id is the case that the first desc was just added by
virtqueue_add_chain_desc().

Best,
Wei

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