Re: [PATCH v2 2/2] virtio_scsi: Implement fc_host

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jan 26, 2017 at 11:41:09AM +0800, Fam Zheng wrote:
> This implements the VIRTIO_SCSI_F_FC_HOST feature by reading the config
> fields and presenting them as sysfs fc_host attributes. The config
> change handler is added here because primary_active will toggle during
> migration.

Looks like there's active discussion on virtio tc mailing list.
It's ok to post patches meanwhile but best as RFC,
and repost after controversy is resolved.

> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  drivers/scsi/virtio_scsi.c | 60 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index ec91bd0..1bb330c 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -28,6 +28,7 @@
>  #include <scsi/scsi_device.h>
>  #include <scsi/scsi_cmnd.h>
>  #include <scsi/scsi_tcq.h>
> +#include <scsi/scsi_transport_fc.h>
>  #include <linux/seqlock.h>
>  
>  #define VIRTIO_SCSI_MEMPOOL_SZ 64
> @@ -795,6 +796,15 @@ static struct scsi_host_template virtscsi_host_template_multi = {
>  	.track_queue_depth = 1,
>  };
>  
> +static struct fc_function_template virtscsi_fc_template = {
> +	.show_host_node_name = 1,
> +	.show_host_port_name = 1,
> +	.show_host_port_type = 1,
> +	.show_host_port_state = 1,
> +};
> +
> +static struct scsi_transport_template *virtscsi_fc_transport_template;
> +
>  #define virtscsi_config_get(vdev, fld) \
>  	({ \
>  		typeof(((struct virtio_scsi_config *)0)->fld) __val; \
> @@ -956,15 +966,42 @@ static int virtscsi_init(struct virtio_device *vdev,
>  	return err;
>  }
>  
> +static void virtscsi_update_fc_host_attrs(struct virtio_device *vdev)
> +{
> +	struct Scsi_Host *shost = vdev->priv;
> +	u8 node_name[8], port_name[8];
> +
> +	if (virtscsi_config_get(vdev, primary_active)) {
> +		virtio_cread_bytes(vdev,
> +			offsetof(struct virtio_scsi_config, primary_wwnn),
> +			&node_name, 8);
> +		virtio_cread_bytes(vdev,
> +			offsetof(struct virtio_scsi_config, primary_wwpn),
> +			&port_name, 8);
> +	} else {
> +		virtio_cread_bytes(vdev,
> +			offsetof(struct virtio_scsi_config, secondary_wwnn),
> +			&node_name, 8);
> +		virtio_cread_bytes(vdev,
> +			offsetof(struct virtio_scsi_config, secondary_wwpn),
> +			&port_name, 8);
> +	}

This is racy, isn't it? You need to wrap this in a generation check
otherwise read can race with primary_active changing.
And you might want a wrapper to virtio_cread_bytes that does not
include generation check.

> +	fc_host_node_name(shost) = wwn_to_u64(node_name);
> +	fc_host_port_name(shost) = wwn_to_u64(port_name);
> +	fc_host_port_type(shost) = FC_PORTTYPE_NPORT;
> +	fc_host_port_state(shost) = FC_PORTSTATE_ONLINE;
> +}
> +
>  static int virtscsi_probe(struct virtio_device *vdev)
>  {
> -	struct Scsi_Host *shost;
> +	struct Scsi_Host *shost = NULL;
>  	struct virtio_scsi *vscsi;
>  	int err;
>  	u32 sg_elems, num_targets;
>  	u32 cmd_per_lun;
>  	u32 num_queues;
>  	struct scsi_host_template *hostt;
> +	bool fc_host_enabled;
>  
>  	if (!vdev->config->get) {
>  		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> @@ -987,6 +1024,9 @@ static int virtscsi_probe(struct virtio_device *vdev)
>  	if (!shost)
>  		return -ENOMEM;
>  
> +	fc_host_enabled = virtio_has_feature(vdev, VIRTIO_SCSI_F_FC_HOST);
> +	if (fc_host_enabled)
> +		shost->transportt = virtscsi_fc_transport_template;
>  	sg_elems = virtscsi_config_get(vdev, seg_max) ?: 1;
>  	shost->sg_tablesize = sg_elems;
>  	vscsi = shost_priv(shost);
> @@ -1032,6 +1072,9 @@ static int virtscsi_probe(struct virtio_device *vdev)
>  	if (err)
>  		goto scsi_add_host_failed;
>  
> +	if (fc_host_enabled)
> +		virtscsi_update_fc_host_attrs(vdev);
> +
>  	virtio_device_ready(vdev);
>  
>  	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
> @@ -1098,6 +1141,11 @@ static int virtscsi_restore(struct virtio_device *vdev)
>  }
>  #endif
>  
> +static void virtscsi_config_changed(struct virtio_device *vdev)
> +{

This is called unconditionally here, will access
invalid config fields if feature is off.
In fact this is wasting an MSIX vector when feature is not
negotiated. No easy way not to, but best document this
in a code comment.

> +	virtscsi_update_fc_host_attrs(vdev);
> +}
> +
>  static struct virtio_device_id id_table[] = {
>  	{ VIRTIO_ID_SCSI, VIRTIO_DEV_ANY_ID },
>  	{ 0 },
> @@ -1109,6 +1157,7 @@ static unsigned int features[] = {
>  #ifdef CONFIG_BLK_DEV_INTEGRITY
>  	VIRTIO_SCSI_F_T10_PI,
>  #endif
> +	VIRTIO_SCSI_F_FC_HOST,
>  };
>  
>  static struct virtio_driver virtio_scsi_driver = {
> @@ -1123,12 +1172,20 @@ static struct virtio_driver virtio_scsi_driver = {
>  	.restore = virtscsi_restore,
>  #endif
>  	.remove = virtscsi_remove,
> +	.config_changed = virtscsi_config_changed,
>  };
>  
>  static int __init init(void)
>  {
>  	int ret = -ENOMEM;
>  
> +	virtscsi_fc_transport_template =
> +		fc_attach_transport(&virtscsi_fc_template);
> +	if (!virtscsi_fc_transport_template) {
> +		pr_err("fc_attach_transport() failed\n");
> +		goto error;
> +	}
> +
>  	virtscsi_cmd_cache = KMEM_CACHE(virtio_scsi_cmd, 0);
>  	if (!virtscsi_cmd_cache) {
>  		pr_err("kmem_cache_create() for virtscsi_cmd_cache failed\n");
> @@ -1176,6 +1233,7 @@ static int __init init(void)
>  
>  static void __exit fini(void)
>  {
> +	fc_release_transport(virtscsi_fc_transport_template);
>  	unregister_virtio_driver(&virtio_scsi_driver);
>  	cpuhp_remove_multi_state(virtioscsi_online);
>  	cpuhp_remove_multi_state(CPUHP_VIRT_SCSI_DEAD);
> -- 
> 2.9.3