From: Chris Lalancette <clalance@redhat.com>
Date: Fri, 18 Jul 2008 10:05:33 +0200
Subject: [xen] fix blkfront to accept > 16 devices
Message-id: 48804ECD.9060006@redhat.com
O-Subject: [RHEL5.3 PATCH 2/5]: Fix blkfront to accept > 16 devices
Bugzilla: 442723
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Mark McLoughlin <markmc@redhat.com>

This patch modifies the blkfront code to accept > 16 devices.  In particular, it
does 2 things:

1)  Makes the blkfront code look in the "virtual-device-ext" node for extended
devices.
2)  Adds another xvd major structure to handle the extended devices.  This is a
little mis-leading, since the major number for extended devices is the same as
normal devices; it's just that we use a different xlbd_type_info structure for
representing the major.

This patch corresponds very closely to the Xen linux-2.6.18-xen.hg c/s 581 and 599.

diff --git a/drivers/xen/blkfront/blkfront.c b/drivers/xen/blkfront/blkfront.c
index bdb34e9..4cfff93 100644
--- a/drivers/xen/blkfront/blkfront.c
+++ b/drivers/xen/blkfront/blkfront.c
@@ -88,8 +88,13 @@ static int blkfront_probe(struct xenbus_device *dev,
 	err = xenbus_scanf(XBT_NIL, dev->nodename,
 			   "virtual-device", "%i", &vdevice);
 	if (err != 1) {
-		xenbus_dev_fatal(dev, err, "reading virtual-device");
-		return err;
+		/* go looking in the extended area instead */
+		err = xenbus_scanf(XBT_NIL, dev->nodename, "virtual-device-ext",
+				   "%i", &vdevice);
+		if (err != 1) {
+			xenbus_dev_fatal(dev, err, "reading virtual-device");
+			return err;
+		}
 	}
 
 	info = kzalloc(sizeof(*info), GFP_KERNEL);
diff --git a/drivers/xen/blkfront/vbd.c b/drivers/xen/blkfront/vbd.c
index 97f094e..6671ca0 100644
--- a/drivers/xen/blkfront/vbd.c
+++ b/drivers/xen/blkfront/vbd.c
@@ -39,6 +39,11 @@
 #define BLKIF_MAJOR(dev) ((dev)>>8)
 #define BLKIF_MINOR(dev) ((dev) & 0xff)
 
+#define EXT_SHIFT 28
+#define EXTENDED (1<<EXT_SHIFT)
+#define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
+#define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
+
 /*
  * For convenience we distinguish between ide, scsi and 'other' (i.e.,
  * potentially combinations of the two) in the naming scheme and in a few other
@@ -47,7 +52,7 @@
 
 #define NUM_IDE_MAJORS 10
 #define NUM_SCSI_MAJORS 17
-#define NUM_VBD_MAJORS 1
+#define NUM_VBD_MAJORS 2
 
 static struct xlbd_type_info xlbd_ide_type = {
 	.partn_shift = 6,
@@ -70,6 +75,13 @@ static struct xlbd_type_info xlbd_vbd_type = {
 	.diskname = "xvd",
 };
 
+static struct xlbd_type_info xlbd_vbd_type_ext = {
+	.partn_shift = 8,
+	.disks_per_major = 256,
+	.devname = "xvd",
+	.diskname = "xvd",
+};
+
 static struct xlbd_major_info *major_info[NUM_IDE_MAJORS + NUM_SCSI_MAJORS +
 					 NUM_VBD_MAJORS];
 
@@ -81,10 +93,6 @@ static struct xlbd_major_info *major_info[NUM_IDE_MAJORS + NUM_SCSI_MAJORS +
 #define XLBD_MAJOR_SCSI_RANGE	XLBD_MAJOR_SCSI_START ... XLBD_MAJOR_VBD_START - 1
 #define XLBD_MAJOR_VBD_RANGE	XLBD_MAJOR_VBD_START ... XLBD_MAJOR_VBD_START + NUM_VBD_MAJORS - 1
 
-/* Information about our VBDs. */
-#define MAX_VBDS 64
-static LIST_HEAD(vbds_list);
-
 static struct block_device_operations xlvbd_block_fops =
 {
 	.owner = THIS_MODULE,
@@ -100,12 +108,14 @@ static struct xlbd_major_info *
 xlbd_alloc_major_info(int major, int minor, int index)
 {
 	struct xlbd_major_info *ptr;
+	int do_register;
 
 	ptr = kzalloc(sizeof(struct xlbd_major_info), GFP_KERNEL);
 	if (ptr == NULL)
 		return NULL;
 
 	ptr->major = major;
+	do_register = 1;
 
 	switch (index) {
 	case XLBD_MAJOR_IDE_RANGE:
@@ -117,32 +127,40 @@ xlbd_alloc_major_info(int major, int minor, int index)
 		ptr->index = index - XLBD_MAJOR_SCSI_START;
 		break;
 	case XLBD_MAJOR_VBD_RANGE:
-		ptr->type = &xlbd_vbd_type;
-		ptr->index = index - XLBD_MAJOR_VBD_START;
+		ptr->index = 0;
+		if ((index - XLBD_MAJOR_VBD_START) == 0)
+			ptr->type = &xlbd_vbd_type;
+		else
+			ptr->type = &xlbd_vbd_type_ext;
+
+		/* 
+		 * if someone already registered block major 202,
+		 * don't try to register it again
+		 */
+		if (major_info[XLBD_MAJOR_VBD_START] != NULL)
+			do_register = 0;
 		break;
 	}
 
-	printk("Registering block device major %i\n", ptr->major);
-	if (register_blkdev(ptr->major, ptr->type->devname)) {
-		WPRINTK("can't get major %d with name %s\n",
-			ptr->major, ptr->type->devname);
-		kfree(ptr);
-		return NULL;
+	if (do_register) {
+		printk("Registering block device major %i\n", ptr->major);
+		if (register_blkdev(ptr->major, ptr->type->devname)) {
+			WPRINTK("can't get major %d with name %s\n",
+				ptr->major, ptr->type->devname);
+			kfree(ptr);
+			return NULL;
+		}
 	}
 
-/*	devfs_mk_dir(ptr->type->devname);*/
 	major_info[index] = ptr;
 	return ptr;
 }
 
 static struct xlbd_major_info *
-xlbd_get_major_info(int vdevice)
+xlbd_get_major_info(int major, int minor, int vdevice)
 {
 	struct xlbd_major_info *mi;
-	int major, minor, index;
-
-	major = BLKIF_MAJOR(vdevice);
-	minor = BLKIF_MINOR(vdevice);
+	int index;
 
 	switch (major) {
 	case IDE0_MAJOR: index = 0; break;
@@ -163,7 +181,12 @@ xlbd_get_major_info(int vdevice)
                 index = 18 + major - SCSI_DISK8_MAJOR;
                 break;
         case SCSI_CDROM_MAJOR: index = 26; break;
-        default: index = 27; break;
+        default:
+		if (!VDEV_IS_EXTENDED(vdevice))
+			index = 27;
+		else
+			index = 28;
+		break;
 	}
 
 	mi = ((major_info[index] != NULL) ? major_info[index] :
@@ -212,7 +235,7 @@ xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
 }
 
 static int
-xlvbd_alloc_gendisk(int minor, blkif_sector_t capacity, int vdevice,
+xlvbd_alloc_gendisk(int major, int minor, blkif_sector_t capacity, int vdevice,
 		    u16 vdisk_info, u16 sector_size,
 		    struct blkfront_info *info)
 {
@@ -226,7 +249,7 @@ xlvbd_alloc_gendisk(int minor, blkif_sector_t capacity, int vdevice,
 	BUG_ON(info->mi != NULL);
 	BUG_ON(info->rq != NULL);
 
-	mi = xlbd_get_major_info(vdevice);
+	mi = xlbd_get_major_info(major, minor, vdevice);
 	if (mi == NULL)
 		goto out;
 	info->mi = mi;
@@ -306,15 +329,30 @@ xlvbd_add(blkif_sector_t capacity, int vdevice, u16 vdisk_info,
 {
 	struct block_device *bd;
 	int err = 0;
+	int major, minor;
+
+	if ((vdevice>>EXT_SHIFT) > 1) {
+		/* this is above the extended range; something is wrong */
+		printk(KERN_WARNING "blkfront: vdevice 0x%x is above the extended range; ignoring\n", vdevice);
+		return -ENODEV;
+	}
 
-	info->dev = MKDEV(BLKIF_MAJOR(vdevice), BLKIF_MINOR(vdevice));
+	if (!VDEV_IS_EXTENDED(vdevice)) {
+		major = BLKIF_MAJOR(vdevice);
+		minor = BLKIF_MINOR(vdevice);
+	}
+	else {
+		major = 202;
+		minor = BLKIF_MINOR_EXT(vdevice);
+	}
 
+	info->dev = MKDEV(major, minor);
 	bd = bdget(info->dev);
 	if (bd == NULL)
 		return -ENODEV;
 
-	err = xlvbd_alloc_gendisk(BLKIF_MINOR(vdevice), capacity, vdevice,
-				  vdisk_info, sector_size, info);
+	err = xlvbd_alloc_gendisk(major, minor, capacity, vdevice, vdisk_info,
+				  sector_size, info);
 
 	bdput(bd);
 	return err;