linux-kernel - Re: Partitions: Amiga RDB partition on 2 TB disk way too big, while OK in AmigaOS 4.1

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Message-ID: <4FDE8450.6090907@earthlink.net>
Date:	Sun, 17 Jun 2012 18:28:48 -0700
From:	jdow <jdow@...thlink.net>
To:	Martin Steigerwald <Martin@...htvoll.de>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	linux-m68k@...r.kernel.org
Subject: Re: Partitions: Amiga RDB partition on 2 TB disk way too big, while
 OK in AmigaOS 4.1

On 2012/06/17 14:20, Martin Steigerwald wrote:
> Am Sonntag, 17. Juni 2012 schrieb jdow:
>> On 2012/06/17 09:36, Geert Uytterhoeven wrote:
>>> On Sun, Jun 17, 2012 at 2:58 PM, Martin Steigerwald
> <Martin@...htvoll.de> wrote:
>>>> Am Sonntag, 17. Juni 2012 schrieb jdow:
>>>> | JXFS 64 bit file system
>>>> |
>>>> | With AmigaOS 4.x a new file system has been introduced called
>>>> | JXFS. It is a totally new 64 bit file system that supports
>>>> | partitions up to 16 TB in size. It is a modern journalling file
>>>> | system, which means that it reduces data loss if data writes to
>>>> | the disk are interrupted. It is the fastest and most reliable
>>>> | file system ever created for AmigaOS.
>>>>
>>>> http://www.amigaos.net/content/1/features
>>>>
>>>> Well I asked AmigaOS 4 developers about this issue as well. Lets see
>>>> what they say about 2 TB limits.
>>>
>>> 16 TB = 2 TB * 8. Perhaps they increased the block size from 512 to
>>> 4096?
>>>
>>> block/partitions/amiga.c reads the block size from
>>> RigidDiskBlock.rdb_BlockBytes,
>>> but after conversion to 512-byte blocks, all further calculations are
>>> done on "int", so it will overflow for disks larger than 2 TiB.
>>>
>>> Note that in your profile-binary.img, the field is 0x200, i.e. 512
>>> bytes per block,
>>> so I'll have to get a deeper look into your RDB first...
> […]
>> Note that the work I did on the Linux RDB code eons ago took full
>> cognizance of the physical and virtual block sizes.
> […]
>> I've asked Martin for a digital copy of his RDBs and what he thinks the
>> partition(s) should look like. I should also be told whether the disk
>> is supposed to be solely Amiga OSs or not. I gather it's not.
>
> Its all in the bug report. profile-binary.img should be it.
>
> Its small so I attach it.
>
> Meanwhile I try to get the currently supported maximum disk size out from
> the OS 4 developers. Maybe JXFS is playing tricks that other filesystems do
> not play or simply has a different implementation.
>
> Thanks,

I've sent Jens a proposed fix changing these lines in amiga.c.
===8<--- was
         struct PartitionBlock *pb;
         int start_sect, nr_sects, blk, part, res = 0;
         int blksize = 1;        /* Multiplier for disk block size */
===8<--- becomes changing line 338 into lines 338-339
         struct PartitionBlock *pb;
         sector_t start_sect, nr_sects;
         int blk, part, res = 0;
         int blksize = 1;        /* Multiplier for disk block size */
===8<---

(I'm working without proper tools at the moment or I'd make a real diff.
Sorry.)

This fix may not be complete. The RDBs contain provisions for describing
the physical disk block size and how many physical blocks are used in a
file system's logical blocks. This MAY not work quite right large physical
block sizes.

{^_^}   Joanne Dow
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