Re: [CFC/CFT] large changes in the loader(8) code

On Tue, Jun 26, 2012 at 04:50:36PM +0400, Andrey V. Elsukov wrote:
> Hi All,
> 
> Some time ago i have started reading the code in the sys/boot.
> Especially i'm interested in the partition tables handling.
> I found several problems:
> 1. There are several copies of the same code in the libi386/biosdisk.c
> and common/disk.c, and partially libpc98/biosdisk.c.
> 2. ZFS probing is very slow, because the ZFS code doesn't know how many
> disks and partitions the system has:
> 	http://www.freebsd.org/cgi/query-pr.cgi?pr=148296
> 	http://www.freebsd.org/cgi/query-pr.cgi?pr=161897
> 3. The GPT support doesn't check CRC and even doesn't know anything
> about the secondary GPT header/table.

Just a quick note here. At some point when I was adding GPT attributes
to allow for test starts I greatly improved, at least parts of, the GPT
implementation. I did implement support for both CRC checksum
verification and fallback to backup GPT header when primary is broken.
And the code is still in sys/boot/common/gpt.c. So my question would be
what do you mean by this sentence?

> So, i have created the branch and committed the changes:
> 	http://svnweb.freebsd.org/base/user/ae/bootcode/
> The patch is here:
> 	http://people.freebsd.org/~ae/boot.diff
> 
> What i already did:
> 1. The partition tables handling now is machine independent,
> and it is compatible with the kernel's GEOM_PART implementation.
> There is new API for disk drivers in the loader to get information
> about partitions and tables:
>         common/Makefile.inc
>  	common/part.c
> 	common/part.h
> 
> 2. The similar and general code from the disk drivers merged in the
> disk.c:
>         common/disk.c
>         common/disk.h
>         i386/libi386/libi386.h
>         i386/libi386/biosdisk.c
>         userboot/test/test.c
>         userboot/userboot/userboot_disk.c
>         userboot/userboot.h
> 3. ZFS code now uses new API and probing on the systems with many disks
> should be greatly increased:
>         zfs/zfs.c
>         i386/loader/main.c
> 4. The gptboot now searches the backup GPT header in the previous sectors,
> when it finds the "GEOM::" signature in the last sector. PMBR code also
> tries to do the same:
>         common/gpt.c
>         i386/pmbr/pmbr.s
> 
> 5. Also the pmbr image now contains one fake partition record.
> When several first sectors are damaged the kernel can't detect GPT
> (see RECOVERING section in the gpart(8)). We can restore PMBR with dd(1)
> command, but the old pmbr image has an empty partition table and
> loader doesn't able to boot from GPT, when there is no partition record
> in the PMBR. Now it will be able. When pmbr is installed via 'gpart bootcode'
> command, the kernel correctly modifies this partition record. So, this is only
> for the first rescue step.
> 
> 6. I have changed userboot interface. I guess there is none consumers except
> the one test program. But if it isn't that, i can make it compatible.
> 
> Any comments are welcome.
> 
> -- 
> WBR, Andrey V. Elsukov
> 
> 



-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
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