[Xen-devel] [PATCH 1/4]: Fix blkfront to accept expanded devices

[Chris Lalancette <clalance@xxxxxxxxxx>]

This patch implements the new extended allocation scheme on the blkfront end.
Note that there is a new xenbus node for the extended stuff, called
"virtual-device-ext".  On a blkfront_probe(), if nothing is found in
"virtual-device", then it will go looking in "virtual-device-ext".  This
prevents old guest kernels from potentially mis-interpreting data in
"virtual-device" (and then subsequently crashing).

Signed-off-by: Chris Lalancette <clalance@xxxxxxxxxx>

diff -r 5201a184f513 drivers/xen/blkfront/blkfront.c
--- a/drivers/xen/blkfront/blkfront.c   Fri Jun 20 17:43:16 2008 +0100
+++ b/drivers/xen/blkfront/blkfront.c   Mon Jun 23 17:56:00 2008 +0200
@@ -92,8 +92,13 @@ static int blkfront_probe(struct xenbus_
        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 -r 5201a184f513 drivers/xen/blkfront/vbd.c
--- a/drivers/xen/blkfront/vbd.c        Fri Jun 20 17:43:16 2008 +0100
+++ b/drivers/xen/blkfront/vbd.c        Mon Jun 23 17:56:00 2008 +0200
@@ -43,6 +43,9 @@
 #define BLKIF_MAJOR(dev) ((dev)>>8)
 #define BLKIF_MINOR(dev) ((dev) & 0xff)
 
+#define VDEV_IS_EXTENDED(dev) (dev & (1<<28))
+#define BLKIF_MINOR_EXT(dev) ((dev)&0x0FFFFFFF)
+
 /*
  * 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
@@ -84,10 +87,6 @@ static struct xlbd_major_info *major_inf
 #define XLBD_MAJOR_IDE_RANGE   XLBD_MAJOR_IDE_START ... XLBD_MAJOR_SCSI_START 
- 1
 #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 =
 {
@@ -144,8 +143,14 @@ xlbd_get_major_info(int vdevice)
        struct xlbd_major_info *mi;
        int major, minor, index;
 
-       major = BLKIF_MAJOR(vdevice);
-       minor = BLKIF_MINOR(vdevice);
+       if (!VDEV_IS_EXTENDED(vdevice)) {
+               major = BLKIF_MAJOR(vdevice);
+               minor = BLKIF_MINOR(vdevice);
+       }
+       else {
+               major = 202;
+               minor = BLKIF_MINOR_EXT(vdevice);
+       }
 
        switch (major) {
        case IDE0_MAJOR: index = 0; break;
@@ -231,6 +236,7 @@ xlvbd_alloc_gendisk(int minor, blkif_sec
        int nr_minors = 1;
        int err = -ENODEV;
        unsigned int offset;
+       int part_shift;
 
        BUG_ON(info->gd != NULL);
        BUG_ON(info->mi != NULL);
@@ -241,15 +247,19 @@ xlvbd_alloc_gendisk(int minor, blkif_sec
                goto out;
        info->mi = mi;
 
-       if ((minor & ((1 << mi->type->partn_shift) - 1)) == 0)
-               nr_minors = 1 << mi->type->partn_shift;
+       part_shift = mi->type->partn_shift;
+       if (VDEV_IS_EXTENDED(vdevice))
+               part_shift += 4;
+
+       if ((minor & ((1 << part_shift) - 1)) == 0)
+               nr_minors = 1 << part_shift;
 
        gd = alloc_disk(nr_minors);
        if (gd == NULL)
                goto out;
 
-       offset =  mi->index * mi->type->disks_per_major +
-                       (minor >> mi->type->partn_shift);
+       offset =  mi->index * mi->type->disks_per_major + (minor >> part_shift);
+
        if (nr_minors > 1) {
                if (offset < 26) {
                        sprintf(gd->disk_name, "%s%c",
@@ -266,13 +276,13 @@ xlvbd_alloc_gendisk(int minor, blkif_sec
                        sprintf(gd->disk_name, "%s%c%d",
                                mi->type->diskname,
                                'a' + offset,
-                               minor & ((1 << mi->type->partn_shift) - 1));
+                               minor & ((1 << part_shift) - 1));
                }
                else {
                        sprintf(gd->disk_name, "%s%c%c%d",
                                mi->type->diskname,
                                'a' + ((offset/26)-1), 'a' + (offset%26),
-                               minor & ((1 << mi->type->partn_shift) - 1));
+                               minor & ((1 << part_shift) - 1));
                }
        }
 
@@ -319,14 +329,26 @@ xlvbd_add(blkif_sector_t capacity, int v
        struct block_device *bd;
        int err = 0;
 
-       info->dev = MKDEV(BLKIF_MAJOR(vdevice), BLKIF_MINOR(vdevice));
+       if (!VDEV_IS_EXTENDED(vdevice)) {
+               info->dev = MKDEV(BLKIF_MAJOR(vdevice), BLKIF_MINOR(vdevice));
+               bd = bdget(info->dev);
+               if (bd == NULL)
+                       return -ENODEV;
 
-       bd = bdget(info->dev);
-       if (bd == NULL)
-               return -ENODEV;
+               err = xlvbd_alloc_gendisk(BLKIF_MINOR(vdevice), capacity,
+                                         vdevice, vdisk_info, sector_size,
+                                         info);
+       }
+       else {
+               info->dev = MKDEV(202, BLKIF_MINOR_EXT(vdevice));
+               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(BLKIF_MINOR_EXT(vdevice), capacity,
+                                         vdevice, vdisk_info, sector_size,
+                                         info);
+       }
 
        bdput(bd);
        return err;

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