wrong CHS limit check

This patch fixes (I think) the grub_biosdisk_rw() CHS limit check, which as described in http://www.allensmith.net/Storage/HDDlimit/Int13h.htm is slightly below LBA-24, not LBA-32 as current code assumes.

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Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call… if you are unable to speak?
(as seen on /.)

2008-03-21  Robert Millan  <[email protected]>

	* disk/i386/pc/biosdisk.c (grub_biosdisk_rw): Fix CHS limit check,
	as per http://www.allensmith.net/Storage/HDDlimit/Int13h.htm

diff -urp grub2/disk/i386/pc/biosdisk.c tmp/disk/i386/pc/biosdisk.c

disk/i386/pc/biosdisk.c +8 -6

@@ -237,15 +237,17 @@ grub_biosdisk_rw (int cmd, grub_disk_t d
     {
       unsigned coff, hoff, soff;
       unsigned head;
-      unsigned real_sector = (unsigned) sector;
 
-      /* It is impossible to reach over 2TB with the traditional
-	 CHS access.  */
-      if (sector > ~0UL)
+      /* It is impossible to reach over 8064 MiB (a bit less than LBA24) with
+	 the traditional CHS access.  */
+      if (sector >
+	  1024 /* cylinders */ *
+	  256 /* heads */ *
+	  63 /* spt */)
 	return grub_error (GRUB_ERR_OUT_OF_RANGE, "out of disk");
 
-      soff = real_sector % data->sectors + 1;
-      head = real_sector / data->sectors;
+      soff = sector % data->sectors + 1;
+      head = sector / data->sectors;
       hoff = head % data->heads;
       coff = head / data->heads;
 

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