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Date:	Thu, 23 Oct 2014 19:24:42 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Pawel Moll <pawel.moll@....com>,
	Ohad Ben-Cohen <ohad@...ery.com>,
	Heinz Graalfs <graalfs@...ux.vnet.ibm.com>,
	virtualization@...ts.linux-foundation.org
Subject: [PATCH RFC v4 11/17] virtio: add legacy feature table support

virtio blk has some legacy feature bits that modern drivers
must not negotiate, but are needed for old legacy hosts
(e.g. that dn't support virtio scsi).
Allow a separate legacy feature table for such cases.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 include/linux/virtio.h  |  4 ++++
 drivers/virtio/virtio.c | 18 +++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d6359a5..f70411e 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -130,6 +130,8 @@ int virtio_device_restore(struct virtio_device *dev);
  * @id_table: the ids serviced by this driver.
  * @feature_table: an array of feature numbers supported by this driver.
  * @feature_table_size: number of entries in the feature table array.
+ * @feature_table_legacy: same as feature_table but when working in legacy mode.
+ * @feature_table_size_legacy: number of entries in feature table legacy array.
  * @probe: the function to call when a device is found.  Returns 0 or -errno.
  * @remove: the function to call when a device is removed.
  * @config_changed: optional function to call when the device configuration
@@ -140,6 +142,8 @@ struct virtio_driver {
 	const struct virtio_device_id *id_table;
 	const unsigned int *feature_table;
 	unsigned int feature_table_size;
+	const unsigned int *feature_table_legacy;
+	unsigned int feature_table_size_legacy;
 	int (*probe)(struct virtio_device *dev);
 	void (*scan)(struct virtio_device *dev);
 	void (*remove)(struct virtio_device *dev);
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 0f44cff..85a164e 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -161,6 +161,7 @@ static int virtio_dev_probe(struct device *_d)
 	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
 	u64 device_features;
 	u64 driver_features;
+	u64 driver_features_legacy;
 	unsigned status;
 
 	/* We have a driver! */
@@ -177,7 +178,22 @@ static int virtio_dev_probe(struct device *_d)
 		driver_features |= (1ULL << f);
 	}
 
-	dev->features = driver_features & device_features;
+	/* Some drivers have a separate feature tables for virtio v1.0 */
+	if (drv->feature_table_legacy) {
+		driver_features_legacy = 0;
+		for (i = 0; i < drv->feature_table_size_legacy; i++) {
+			unsigned int f = drv->feature_table_legacy[i];
+			BUG_ON(f >= 64);
+			driver_features_legacy |= (1ULL << f);
+		}
+	} else {
+		driver_features_legacy = driver_features;
+	}
+
+	if (driver_features & device_features & (1ULL << VIRTIO_F_VERSION_1))
+		dev->features = driver_features & device_features;
+	else
+		dev->features = driver_features_legacy & device_features;
 
 	/* Transport features always preserved to pass to finalize_features. */
 	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
-- 
MST

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