[SLOF] [PATCH] slof/fs/packages/disk-label.fs: improve checking for DOS boot partitions

[Kautuk Consul]

While testing with a qcow2 with a DOS boot partition it was found that
when we set the logical_block_size in the guest XML to >512 then the
boot would fail in the following interminable loop:
<SNIP>
Trying to load:  from: /pci at 800000020000000/scsi at 3 ... virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
</SNIP>

Change the count-dos-logical-partitions Forth subroutine and the Forth
subroutines calling count-dos-logical-partitions to check for this access
beyond end of device error.

After making the above changes, it fails properly with the correct error
message as follows:
<SNIP>
Trying to load:  from: /pci at 800000020000000/scsi at 3 ... virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!

E3404: Not a bootable device!

E3407: Load failed

  Type 'boot' and press return to continue booting the system.
  Type 'reset-all' and press return to reboot the system.

Ready!
0 >
</SNIP>

Signed-off-by: Kautuk Consul <kconsul at linux.vnet.ibm.com>
---
 slof/fs/packages/disk-label.fs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/slof/fs/packages/disk-label.fs b/slof/fs/packages/disk-label.fs
index 661c6b0..e680847 100644
--- a/slof/fs/packages/disk-label.fs
+++ b/slof/fs/packages/disk-label.fs
@@ -139,6 +139,13 @@ CONSTANT /gpt-part-entry
    block block-size read drop    \ read sector
 ;
 
+\ read sector to array "block" and return actual bytes read
+: read-sector-ret ( sector-number -- actual)
+   \ block-size is 0x200 on disks, 0x800 on cdrom drives
+   block-size * 0 seek drop      \ seek to sector
+   block block-size read    \ read sector
+;
+
 : (.part-entry) ( part-entry )
    cr ." part-entry>active:        " dup part-entry>active c@ .d
    cr ." part-entry>start-head:    " dup part-entry>start-head c@ .d
@@ -204,7 +211,8 @@ CONSTANT /gpt-part-entry
          part-entry>sector-offset l at -le    ( current sector )
          dup to part-start to lpart-start  ( current )
          BEGIN
-            part-start read-sector          \ read EBR
+            part-start read-sector-ret          \ read EBR
+            block-size < IF UNLOOP 0 EXIT THEN
             1 partition>start-sector IF
                \ ." Logical Partition found at " part-start .d cr
                1+
@@ -279,6 +287,7 @@ CONSTANT /gpt-part-entry
    THEN
 
    count-dos-logical-partitions TO dos-logical-partitions
+   dos-logical-partitions 0= IF false EXIT THEN
 
    debug-disk-label? IF
       ." Found " dos-logical-partitions .d ." logical partitions" cr
@@ -352,6 +361,7 @@ CONSTANT /gpt-part-entry
    no-mbr? IF drop FALSE EXIT THEN  \ read MBR and check for DOS disk-label magic
 
    count-dos-logical-partitions TO dos-logical-partitions
+   dos-logical-partitions 0= IF 0 EXIT THEN
 
    debug-disk-label? IF
       ." Found " dos-logical-partitions .d ." logical partitions" cr
-- 
2.31.1