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authorRusty Russell <rusty@rustcorp.com.au>2008-08-26 00:19:27 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-08-26 00:19:28 +1000
commit1dc3e3bcbfe335843ec938bfdddb34d10f4dd278 (patch)
tree8666189f7a285c8e4c6512784dff39971fefa30c /drivers/lguest/lguest_device.c
parentbf2002967775cbb233876d51ff94e8daa7e77858 (diff)
lguest: update commentry
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'drivers/lguest/lguest_device.c')
-rw-r--r--drivers/lguest/lguest_device.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 37344aaee22..a661bbdae3d 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -98,6 +98,10 @@ static u32 lg_get_features(struct virtio_device *vdev)
return features;
}
+/* The virtio core takes the features the Host offers, and copies the
+ * ones supported by the driver into the vdev->features array. Once
+ * that's all sorted out, this routine is called so we can tell the
+ * Host which features we understand and accept. */
static void lg_finalize_features(struct virtio_device *vdev)
{
unsigned int i, bits;
@@ -108,6 +112,10 @@ static void lg_finalize_features(struct virtio_device *vdev)
/* Give virtio_ring a chance to accept features. */
vring_transport_features(vdev);
+ /* The vdev->feature array is a Linux bitmask: this isn't the
+ * same as a the simple array of bits used by lguest devices
+ * for features. So we do this slow, manual conversion which is
+ * completely general. */
memset(out_features, 0, desc->feature_len);
bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
for (i = 0; i < bits; i++) {