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Date: Tue, 15 Mar 2011 15:16:44 +0100
From: Christoph Hellwig <hch@....de>
To: qemu-devel@...gnu.org, linux-kernel@...r.kernel.org
Cc: stefanha@...il.com, kwolf@...hat.com, prerna@...ux.vnet.ibm.com,
aliguori@...ibm.com, rusty@...tcorp.com.au
Subject: [PATCH, RFC] virtio_blk: add cache control support
Add support for the new dynamic features config space field to allow
en/disabling the write cache at runtime. The userspace interface is
a SCSI-compatible sysfs attribute.
Signed-off-by: Christoph Hellwig <hch@....de>
Index: linux-2.6/drivers/block/virtio_blk.c
===================================================================
--- linux-2.6.orig/drivers/block/virtio_blk.c 2011-03-15 12:16:29.156133695 +0100
+++ linux-2.6/drivers/block/virtio_blk.c 2011-03-15 13:17:30.160634723 +0100
@@ -291,6 +291,73 @@ static ssize_t virtblk_serial_show(struc
}
DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);
+static bool virtblk_has_wb_cache(struct virtio_blk *vblk)
+{
+ struct virtio_device *vdev = vblk->vdev;
+ u32 features;
+
+ if (!virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+ return false;
+ if (!virtio_has_feature(vdev, VIRTIO_BLK_F_DYNAMIC))
+ return true;
+
+ vdev->config->get(vdev, offsetof(struct virtio_blk_config, features),
+ &features, sizeof(features));
+
+ if (features & VIRTIO_BLK_RT_WCE)
+ return true;
+ return false;
+}
+
+static ssize_t virtblk_cache_type_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+
+ if (virtblk_has_wb_cache(disk->private_data))
+ return sprintf(buf, "write back\n");
+ else
+ return sprintf(buf, "write through\n");
+}
+
+static ssize_t virtblk_cache_type_store(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t count)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+ struct virtio_blk *vblk = disk->private_data;
+ struct virtio_device *vdev = vblk->vdev;
+ u32 features, features2 = 0;
+
+ if (!virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH) ||
+ !virtio_has_feature(vdev, VIRTIO_BLK_F_DYNAMIC))
+ return -ENXIO;
+
+ if (strncmp(buf, "write through", sizeof("write through") - 1) == 0) {
+ ;
+ } else if (strncmp(buf, "write back", sizeof("write back") - 1) == 0) {
+ blk_queue_flush(disk->queue, REQ_FLUSH);
+ features |= VIRTIO_BLK_RT_WCE;
+ } else {
+ return -EINVAL;
+ }
+
+ vdev->config->set(vdev, offsetof(struct virtio_blk_config, features),
+ &features, sizeof(features));
+
+ vdev->config->get(vdev, offsetof(struct virtio_blk_config, features),
+ &features2, sizeof(features2));
+
+ if ((features & VIRTIO_BLK_RT_WCE) !=
+ (features2 & VIRTIO_BLK_RT_WCE))
+ return -EIO;
+
+ if (!(features2 & VIRTIO_BLK_RT_WCE))
+ blk_queue_flush(disk->queue, 0);
+ return count;
+}
+static DEVICE_ATTR(cache_type, S_IRUGO|S_IWUSR,
+ virtblk_cache_type_show, virtblk_cache_type_store);
+
static int __devinit virtblk_probe(struct virtio_device *vdev)
{
struct virtio_blk *vblk;
@@ -377,7 +444,7 @@ static int __devinit virtblk_probe(struc
index++;
/* configure queue flush support */
- if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+ if (virtblk_has_wb_cache(vblk))
blk_queue_flush(q, REQ_FLUSH);
/* If disk is read-only in the host, the guest should obey */
@@ -456,6 +523,10 @@ static int __devinit virtblk_probe(struc
if (err)
goto out_del_disk;
+ err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_cache_type);
+ if (err)
+ goto out_del_disk;
+
return 0;
out_del_disk:
@@ -499,7 +570,7 @@ static const struct virtio_device_id id_
static unsigned int features[] = {
VIRTIO_BLK_F_SEG_MAX, VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_GEOMETRY,
VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE, VIRTIO_BLK_F_SCSI,
- VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY
+ VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_DYNAMIC
};
/*
Index: linux-2.6/include/linux/virtio_blk.h
===================================================================
--- linux-2.6.orig/include/linux/virtio_blk.h 2011-03-15 12:14:28.261632780 +0100
+++ linux-2.6/include/linux/virtio_blk.h 2011-03-15 12:25:56.308634399 +0100
@@ -16,6 +16,7 @@
#define VIRTIO_BLK_F_SCSI 7 /* Supports scsi command passthru */
#define VIRTIO_BLK_F_FLUSH 9 /* Cache flush command support */
#define VIRTIO_BLK_F_TOPOLOGY 10 /* Topology information is available */
+#define VIRTIO_BLK_F_DYNAMIC 11 /* Dynamic features field */
#define VIRTIO_BLK_ID_BYTES 20 /* ID string length */
@@ -45,6 +46,9 @@ struct virtio_blk_config {
__u16 min_io_size;
/* optimal sustained I/O size in logical blocks. */
__u32 opt_io_size;
+ /* runtime controllable features */
+ __u32 features;
+#define VIRTIO_BLK_RT_WCE (1 << 0)
} __attribute__((packed));
--
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