Subject: Propagate changed size of VBDs
References: bnc#583677
Patch-mainline: n/a

Support dynamic resizing of virtual block devices. This patch supports
both file backed block devices as well as physical devices that can be
dynamically resized on the host side.

Signed-off-by: K. Y. Srinivasan <ksrinivasan@xxxxxxxxxx>

Index: linux/drivers/xen/blkback/blkback.c
===================================================================
--- linux.orig/drivers/xen/blkback/blkback.c	2010-03-18 14:17:28.000000000 -0600
+++ linux/drivers/xen/blkback/blkback.c	2010-03-18 14:17:33.000000000 -0600
@@ -209,6 +209,7 @@ static void print_stats(blkif_t *blkif)
 int blkif_schedule(void *arg)
 {
 	blkif_t *blkif = arg;
+	struct vbd *vbd = &blkif->vbd;
 
 	blkif_get(blkif);
 
@@ -218,6 +219,8 @@ int blkif_schedule(void *arg)
 	while (!kthread_should_stop()) {
 		if (try_to_freeze())
 			continue;
+		if (unlikely(vbd->size != vbd_size(vbd)))
+			vbd_resize(blkif);
 
 		wait_event_interruptible(
 			blkif->wq,
Index: linux/drivers/xen/blkback/vbd.c
===================================================================
--- linux.orig/drivers/xen/blkback/vbd.c	2010-03-18 14:17:28.000000000 -0600
+++ linux/drivers/xen/blkback/vbd.c	2010-03-18 14:17:33.000000000 -0600
@@ -73,6 +73,7 @@ int vbd_create(blkif_t *blkif, blkif_vde
 	}
 
 	vbd->bdev = bdev;
+	vbd->size = vbd_size(vbd);
 
 	if (vbd->bdev->bd_disk == NULL) {
 		DPRINTK("vbd_creat: device %08x doesn't exist.\n",
@@ -120,3 +121,45 @@ int vbd_translate(struct phys_req *req,
  out:
 	return rc;
 }
+
+void vbd_resize(blkif_t *blkif)
+{
+	struct vbd *vbd = &blkif->vbd;
+	struct xenbus_transaction xbt;
+	int err;
+	struct xenbus_device *dev = blkif->be->dev;
+	unsigned long long new_size = vbd_size(vbd);
+
+	printk(KERN_INFO "VBD Resize: new size %Lu\n", new_size);
+	vbd->size = new_size;
+again:
+	err = xenbus_transaction_start(&xbt);
+	if (err) {
+		printk(KERN_WARNING "Error starting transaction");
+		return;
+	}
+	err = xenbus_printf(xbt, dev->nodename, "sectors", "%Lu",
+			    vbd_size(vbd));
+	if (err) {
+		printk(KERN_WARNING "Error writing new size");
+		goto abort;
+	}
+	/*
+	 * Write the current state; we will use this to synchronize
+	 * the front-end. If the current state is "connected" the
+	 * front-end will get the new size information online.
+	 */
+	err = xenbus_printf(xbt, dev->nodename, "state", "%d", dev->state);
+	if (err) {
+		printk(KERN_WARNING "Error writing the state");
+		goto abort;
+	}
+
+	err = xenbus_transaction_end(xbt, 0);
+	if (err == -EAGAIN)
+		goto again;
+	if (err)
+		printk(KERN_WARNING "Error ending transaction");
+abort:
+	xenbus_transaction_end(xbt, 1);
+}
Index: linux/drivers/xen/blkback/common.h
===================================================================
--- linux.orig/drivers/xen/blkback/common.h	2010-03-18 14:17:28.000000000 -0600
+++ linux/drivers/xen/blkback/common.h	2010-03-18 14:17:33.000000000 -0600
@@ -56,6 +56,7 @@ struct vbd {
 	unsigned char  type;        /* VDISK_xxx */
 	u32            pdevice;     /* phys device that this vbd maps to */
 	struct block_device *bdev;
+	sector_t       size;        /* Cached size parameter */
 };
 
 struct backend_info;
@@ -116,6 +117,7 @@ blkif_t *blkif_alloc(domid_t domid);
 void blkif_disconnect(blkif_t *blkif);
 void blkif_free(blkif_t *blkif);
 int blkif_map(blkif_t *blkif, unsigned long shared_page, unsigned int evtchn);
+void vbd_resize(blkif_t *blkif);
 
 #define blkif_get(_b) (atomic_inc(&(_b)->refcnt))
 #define blkif_put(_b)					\
Index: linux/drivers/xen/blkfront/blkfront.c
===================================================================
--- linux.orig/drivers/xen/blkfront/blkfront.c	2010-03-18 14:17:28.000000000 -0600
+++ linux/drivers/xen/blkfront/blkfront.c	2010-03-18 14:17:33.000000000 -0600
@@ -328,9 +328,25 @@ static void connect(struct blkfront_info
 	unsigned int binfo;
 	int err;
 
-	if ((info->connected == BLKIF_STATE_CONNECTED) ||
-	    (info->connected == BLKIF_STATE_SUSPENDED) )
+	switch (info->connected) {
+	case BLKIF_STATE_CONNECTED:
+		/*
+		 * Potentially, the back-end may be signalling
+		 * a capacity change; update the capacity.
+		 */
+		err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+				   "sectors", "%Lu", &sectors);
+		if (XENBUS_EXIST_ERR(err))
+			return;
+		printk(KERN_INFO "Setting capacity to %Lu\n",
+		       sectors);
+		set_capacity(info->gd, sectors);
+		revalidate_disk(info->gd);
+
+		/* fall through */
+	case BLKIF_STATE_SUSPENDED:
 		return;
+	}
 
 	DPRINTK("blkfront.c:connect:%s.\n", info->xbdev->otherend);