block: Expand Xen blkfront for > 16 xvd

Until recently, the maximum number of xvd block devices you could attach
to a Xen domU was 16. This limitation turned out to be problematic for
some users, so it was expanded to handle a much larger number of disks.
However, this requires a couple of changes in the way that blkfront
scans for disks. This functionality is already present in the Xen
linux-2.6.18-xen.hg tree; the attached patch adds this functionality to
the mainline xen-blkfront implementation. I successfully tested it on a
2.6.25 tree, and build tested it on 2.6.27-rc3.

Signed-off-by: Chris Lalancette <clalance@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 55 insertions, 21 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 3ca643cafcc..bff602ccccf 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -105,15 +105,17 @@ static DEFINE_SPINLOCK(blkif_io_lock);
 #define GRANT_INVALID_REF       0
 
 #define PARTS_PER_DISK          16
+#define PARTS_PER_EXT_DISK      256
 
 #define BLKIF_MAJOR(dev) ((dev)>>8)
 #define BLKIF_MINOR(dev) ((dev) & 0xff)
 
-#define DEV_NAME        "xvd"   /* name in /dev */
+#define EXT_SHIFT 28
+#define EXTENDED (1<<EXT_SHIFT)
+#define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
+#define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
 
-/* Information about our VBDs. */
-#define MAX_VBDS 64
-static LIST_HEAD(vbds_list);
+#define DEV_NAME        "xvd"   /* name in /dev */
 
 static int get_id_from_freelist(struct blkfront_info *info)
 {
@@ -386,31 +388,60 @@ static int xlvbd_barrier(struct blkfront_info *info)
 }
 
 
-static int xlvbd_alloc_gendisk(int minor, blkif_sector_t capacity,
-                               int vdevice, u16 vdisk_info, u16 sector_size,
-                               struct blkfront_info *info)
+static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
+                               struct blkfront_info *info,
+                               u16 vdisk_info, u16 sector_size)
 {
         struct gendisk *gd;
         int nr_minors = 1;
         int err = -ENODEV;
+        unsigned int offset;
+        int minor;
+        int nr_parts;
 
         BUG_ON(info->gd != NULL);
         BUG_ON(info->rq != NULL);
 
-        if ((minor % PARTS_PER_DISK) == 0)
-                nr_minors = PARTS_PER_DISK;
+        if ((info->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", info->vdevice);
+                return -ENODEV;
+        }
+
+        if (!VDEV_IS_EXTENDED(info->vdevice)) {
+                minor = BLKIF_MINOR(info->vdevice);
+                nr_parts = PARTS_PER_DISK;
+        } else {
+                minor = BLKIF_MINOR_EXT(info->vdevice);
+                nr_parts = PARTS_PER_EXT_DISK;
+        }
+
+        if ((minor % nr_parts) == 0)
+                nr_minors = nr_parts;
 
         gd = alloc_disk(nr_minors);
         if (gd == NULL)
                 goto out;
 
-        if (nr_minors > 1)
-                sprintf(gd->disk_name, "%s%c", DEV_NAME,
-                        'a' + minor / PARTS_PER_DISK);
-        else
-                sprintf(gd->disk_name, "%s%c%d", DEV_NAME,
-                        'a' + minor / PARTS_PER_DISK,
-                        minor % PARTS_PER_DISK);
+        offset = minor / nr_parts;
+
+        if (nr_minors > 1) {
+                if (offset < 26)
+                        sprintf(gd->disk_name, "%s%c", DEV_NAME, 'a' + offset);
+                else
+                        sprintf(gd->disk_name, "%s%c%c", DEV_NAME,
+                                'a' + ((offset / 26)-1), 'a' + (offset % 26));
+        } else {
+                if (offset < 26)
+                        sprintf(gd->disk_name, "%s%c%d", DEV_NAME,
+                                'a' + offset,
+                                minor & (nr_parts - 1));
+                else
+                        sprintf(gd->disk_name, "%s%c%c%d", DEV_NAME,
+                                'a' + ((offset / 26) - 1),
+                                'a' + (offset % 26),
+                                minor & (nr_parts - 1));
+        }
 
         gd->major = XENVBD_MAJOR;
         gd->first_minor = minor;
@@ -699,8 +730,13 @@ 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);
@@ -861,9 +897,7 @@ static void blkfront_connect(struct blkfront_info *info)
         if (err)
                 info->feature_barrier = 0;
 
-        err = xlvbd_alloc_gendisk(BLKIF_MINOR(info->vdevice),
-                                  sectors, info->vdevice,
-                                  binfo, sector_size, info);
+        err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
         if (err) {
                 xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
                                  info->xbdev->otherend);