[SLOF] [PATCH] virtio: Remove global variables in block and 9p driver

[Thomas Huth]

On 01.02.2017 03:14, Alexey Kardashevskiy wrote:
> On 18/01/17 00:16, Thomas Huth wrote:
>> No need for a global variable to store the virtqueue information here,
>> thus let's remove the global vq variable and make it local to the
>> init function instead.
>>
>> Signed-off-by: Thomas Huth <thuth at redhat.com>
>> ---
>>  lib/libvirtio/virtio-9p.c  | 9 +++------
>>  lib/libvirtio/virtio-blk.c | 9 +++------
>>  2 files changed, 6 insertions(+), 12 deletions(-)
>>
>> diff --git a/lib/libvirtio/virtio-9p.c b/lib/libvirtio/virtio-9p.c
>> index 6e9c379..fb329b3 100644
>> --- a/lib/libvirtio/virtio-9p.c
>> +++ b/lib/libvirtio/virtio-9p.c
>> @@ -20,8 +20,6 @@
>>  #include "p9.h"
>>  #include "virtio-internal.h"
>>  
>> -static struct vqs vq;
>> -
>>  /**
>>   * Notes for 9P Server config:
>>   *
>> @@ -163,7 +161,7 @@ static int virtio_9p_transact(void *opaque, uint8_t *tx, int tx_size, uint8_t *r
>>  int virtio_9p_init(struct virtio_device *dev, void *tx_buf, void *rx_buf,
>>  		   int buf_size)
>>  {
>> -	struct vring_avail *vq_avail;
>> +	struct vqs vq;
>>  	int status = VIRTIO_STAT_ACKNOWLEDGE;
>>  
>>  	/* Check for double open */
>> @@ -195,9 +193,8 @@ int virtio_9p_init(struct virtio_device *dev, void *tx_buf, void *rx_buf,
>>  	if (virtio_queue_init_vq(dev, &vq, 0))
>>  		goto dev_error;
>>  
>> -	vq_avail = virtio_get_vring_avail(dev, 0);
>> -	vq_avail->flags = virtio_cpu_to_modern16(dev, VRING_AVAIL_F_NO_INTERRUPT);
>> -	vq_avail->idx = 0;
>> +	vq.avail->flags = virtio_cpu_to_modern16(dev, VRING_AVAIL_F_NO_INTERRUPT);
>> +	vq.avail->idx = 0;
> 
> 
> Here is some black magic happening which I cannot understand. @vq is a
> local struct, it is not used anywhere except virtio_queue_init_vq() but
> even there the only used bit is vq->desc which is allocated in
> virtio_queue_init_vq() and then written to @dev via virtio_set_qaddr().
> 
> I'd think that we do not need @vq parameter in virtio_queue_init_vq() and
> we can drop these local @vq from "virtio_.*_init", what do I miss?

You missed that the "virtqueue available ring" is used again in
virtio_9p_transact(). The code gets a pointer to the ring there with
virtio_get_vring_avail(). So no, this "black magic" can not be dropped,
it is a required setup step.

 Thomas