Subject: Re: [PATCH SLOF 4/5] disk-label: add support for booting from GPT FAT partition

From: Nikunj A Dadhania <[email-masked]>
Date: Wed, 24 Jun 2015 11:03:34 +0530

Thomas Huth <[email-masked]> writes:

> On Mon, 22 Jun 2015 13:29:46 +0530
> Nikunj A Dadhania <[email-masked]> wrote:
>
>> For a GPT+LVM combination disk, older bootloader that does not support
>> LVM, cannot load kernel from LVM.
>> 
>> The patch add support to read from BASIC_DATA UUID
>> partition. Installer has installed CHRP-BOOT config on a FAT file
>> system.
>
> Maybe better: The patch adds support to read from BASIC_DATA UUID
> partitions for the case that the OS installer has installed
> the CHRP-BOOT config on a FAT file system.
>
> ?
>
>> Signed-off-by: Nikunj A Dadhania <[email-masked]>
>> ---
>>  slof/fs/packages/disk-label.fs | 54 +++++++++++++++++++++++++++++++++++++-----
>>  1 file changed, 48 insertions(+), 6 deletions(-)
>> 
>> diff --git a/slof/fs/packages/disk-label.fs b/slof/fs/packages/disk-label.fs
>> index e317e93..821e959 100644
>> --- a/slof/fs/packages/disk-label.fs
>> +++ b/slof/fs/packages/disk-label.fs
>> @@ -266,7 +266,10 @@ CONSTANT /gpt-part-entry
>>  
>>  : try-dos-partition ( -- okay? )
>>     \ Read partition table and check magic.
>> -   no-mbr? IF cr ." No DOS disk-label found." cr false EXIT THEN
>> +   no-mbr? IF
>> +       debug-disk-label? IF cr ." No DOS disk-label found." cr THEN
>> +       false EXIT
>> +   THEN
>>  
>>     count-dos-logical-partitions TO dos-logical-partitions
>>  
>> @@ -381,18 +384,38 @@ AA268B49521E5A8B    CONSTANT GPT-PREP-PARTITION-4
>>     TRUE
>>  ;
>>  
>> -: load-from-gpt-prep-partition ( addr -- size )
>> +\ Check for GPT MSFT BASIC DATA GUID - fat based
>> +EBD0A0A2            CONSTANT GPT-BASIC-DATA-PARTITION-1
>> +B9E5                CONSTANT GPT-BASIC-DATA-PARTITION-2
>> +4433                CONSTANT GPT-BASIC-DATA-PARTITION-3
>> +87C068B6B72699C7    CONSTANT GPT-BASIC-DATA-PARTITION-4
>> +
>> +: gpt-basic-data-partition? ( -- true|false )
>> +   block gpt-part-entry>part-type-guid
>> +   dup l@-le     GPT-BASIC-DATA-PARTITION-1 <> IF DROP FALSE EXIT THEN
>> +   dup 4 + w@-le GPT-BASIC-DATA-PARTITION-2 <> IF DROP FALSE EXIT THEN
>> +   dup 6 + w@-le GPT-BASIC-DATA-PARTITION-3 <> IF DROP FALSE EXIT THEN
>> +       8 + x@    GPT-BASIC-DATA-PARTITION-4 <> IF FALSE EXIT THEN
>> +   TRUE
>> +;
>> +
>> +\ Can be called from two path
>> +\ 1) load-from-boot-partition for GPT PReP partition
>> +\ 2) try-partitions for gpt basic data partition having fat chrp-boot
>
> What did you want to achieve with the above comment? Caller locations
> can change with later patches, but it's unlikely that everybody
> remembers to update such comments in that case. So unlikely you've got
> a good reason for above comment (but in that case, it maybe should be
> written in a different way), I'd suggest to drop it.

I will redo this word and split it so that do not have confusing
signature.

>
>> +: load-from-gpt-partition ( [ addr ] -- size | TRUE )
>
> What do you mean with addr in square brackets? Is it optional?
>
>>     no-gpt? IF drop FALSE EXIT THEN
>>     debug-disk-label? IF
>>        cr ." GPT partition found " cr
>>     THEN
>> -   1 read-sector block gpt>part-entry-lba l@-le
>> +   1 read-sector block gpt>part-entry-lba x@-le
>>     block-size * to seek-pos
>>     block gpt>part-entry-size l@-le to gpt-part-size
>>     block gpt>num-part-entry l@-le dup 0= IF FALSE EXIT THEN
>>     1+ 1 ?DO
>>        seek-pos 0 seek drop
>> -      block gpt-part-size read drop gpt-prep-partition? IF
>> +       block gpt-part-size read drop
>> +       gpt-prep-partition? IF
>
> You've changed the level of indentation here. Please try to avoid that
> (unless you've got a good reason, e.g. because the previous indentation
> was obviously wrong)

Not intentional, I try to make sure I do not change the indentation.

>
>>           debug-disk-label? IF
>>              ." GPT PReP partition found " cr
>>           THEN
>> @@ -404,6 +427,24 @@ AA268B49521E5A8B    CONSTANT GPT-PREP-PARTITION-4
>>           0 0 seek drop             ( addr len )
>>           block-size * read         ( size )
>>           UNLOOP EXIT
>> +     THEN
>> +     gpt-basic-data-partition? IF
>
> Hmm, I wonder whether we need a proper coding conventions spec for
> writing Forth code ... (at least about the indentation depths ...) ;-)
>
>> +         debug-disk-label? IF
>> +            ." GPT LINUX DATA partition found " cr
>> +         THEN
>> +         block gpt-part-entry>first-lba x@ xbflip
>> +         dup to part-start
>> +         block gpt-part-entry>last-lba x@ xbflip
>> +         over - 1+                 ( addr offset len )
>> +         dup block-size * to part-size
>> +         swap                      ( addr len offset )
>> +         block-size * to part-offset
>> +         0 0 seek
>> +         block block-size read
>> +         3drop
>> +         block has-fat-filesystem 0= IF false UNLOOP EXIT THEN
>> +         TRUE
>> +         UNLOOP EXIT
>>        THEN
>>        seek-pos gpt-part-size i * + to seek-pos
>>     LOOP
>> @@ -495,11 +536,11 @@ AA268B49521E5A8B    CONSTANT GPT-PREP-PARTITION-4
>>  
>>     debug-disk-label? IF ." Trying CHRP boot " .s cr THEN
>>     1 disk-chrp-boot !
>> -   dup load-chrp-boot-file ?dup 0 <> IF .s cr nip EXIT THEN
>> +   dup load-chrp-boot-file ?dup 0 <> IF nip EXIT THEN
>>     0 disk-chrp-boot !
>>  
>>     debug-disk-label? IF ." Trying GPT boot " .s cr THEN
>> -   load-from-gpt-prep-partition
>> +   load-from-gpt-partition
>
> So here the function is called with an "addr" parameter on the stack ...
>
>>     \ More boot partition formats ...
>>  ;
>>  
>> @@ -594,6 +635,7 @@ AA268B49521E5A8B    CONSTANT GPT-PREP-PARTITION-4
>>  
>>  : try-partitions ( -- found? )
>>     try-dos-partition IF try-files EXIT THEN
>> +   load-from-gpt-partition IF try-files EXIT THEN
>
> ... but here it is called without an "addr" parameter? *Confusing*
> How does this work?

Yes :-)

Let me rework on this to break it up for readabilty and better stack
debugging.

Regards
Nikunj