Blkfront support for get geometry ioctl

[Stephen Childs <Stephen.Childs@cs.tcd.ie>]

Hi,

Continuing my battle with LCFGng installation onto Xen, I was puzzled by the 
fact that whatever size drive I exported to Xen, the partitioning program 
always seemed to think the disk size was approx 2.1 GB. After some probing, 
I realised that the program LCFG uses to determine disk size (based on 
RedHat's libfdisk I think) does so by performing an ioctl to get the 
geometry of the disk. The code in blkfront "implements" the HDIO_GETGEO 
ioctl by returning garbage results for cyls, heads, and sectors/track. (the 
figures in question: 63*255*262 -- equals approx 2.1 GB!).

Do you think it would be possible to return geometry values that are at 
least consistent with the size of the device? Something like this (still has 
hard-coded heads and sectors, but calculates cyls based on size of disk):

--- 
xeno-unstable-pristine/linux-2.6.8.1-xen-sparse/drivers/xen/blkfront/blkfront.c 
     Wed Sep  1 10:45:33 2004
+++ 
xeno-unstable.bk/linux-2.6.8.1-xen-sparse/drivers/xen/blkfront/blkfront.c 
Wed Sep  1 10:46:27 2004
@@ -510,6 +510,8 @@
      struct gendisk *gd;
      struct hd_struct *part;
      int i;
+    unsigned short cylinders;
+    byte heads, sectors;

      /* NB. No need to check permissions. That is done for us. */

@@ -554,23 +556,39 @@
          break;

      case HDIO_GETGEO:
-        /* note: these values are complete garbage */
          DPRINTK_IOCTL("   HDIO_GETGEO: %x\n", HDIO_GETGEO);
          if (!argument) return -EINVAL;
+
+        /* We don't have real geometry info, but let's at least return
+          values consistent with the size of the device */
+
+        heads = 0xff;
+        sectors = 0x3f;
+        cylinders = part->nr_sects / (heads * sectors);
+
          if (put_user(0x00,  (unsigned long *) &geo->start)) return -EFAULT;
-        if (put_user(0xff,  (byte *)&geo->heads)) return -EFAULT;
-        if (put_user(0x3f,  (byte *)&geo->sectors)) return -EFAULT;
-        if (put_user(0x106, (unsigned short *)&geo->cylinders)) return -EFAULT;
+        if (put_user(heads,  (byte *)&geo->heads)) return -EFAULT;
+        if (put_user(sectors,  (byte *)&geo->sectors)) return -EFAULT;
+        if (put_user(cylinders, (unsigned short *)&geo->cylinders)) return 
-EFAULT;
+
          return 0;

      case HDIO_GETGEO_BIG:
-        /* note: these values are complete garbage */
          DPRINTK_IOCTL("   HDIO_GETGEO_BIG: %x\n", HDIO_GETGEO_BIG);
          if (!argument) return -EINVAL;
+
+        /* We don't have real geometry info, but let's at least return
+          values consistent with the size of the device */
+
+        heads = 0xff;
+        sectors = 0x3f;
+        cylinders = part->nr_sects / (heads * sectors);
+
          if (put_user(0x00,  (unsigned long *) &geo->start))  return -EFAULT;
-        if (put_user(0xff,  (byte *)&geo->heads))   return -EFAULT;
-        if (put_user(0x3f,  (byte *)&geo->sectors)) return -EFAULT;
-        if (put_user(0x106, (unsigned int *) &geo->cylinders)) return -EFAULT;
+        if (put_user(heads,  (byte *)&geo->heads))   return -EFAULT;
+        if (put_user(sectors,  (byte *)&geo->sectors)) return -EFAULT;
+        if (put_user(cylinders, (unsigned int *) &geo->cylinders)) return 
-EFAULT;
+
          return 0;

      case CDROMMULTISESSION:

-- 
Dr. Stephen Childs,
Research Fellow, EGEE Project,    phone:                    +353-1-6081720
Computer Architecture Group,      email:        Stephen.Childs @ cs.tcd.ie
Trinity College Dublin, Ireland   web: http://www.cs.tcd.ie/Stephen.Childs


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