Re: Subject: [PATCH RFC] block: fix Amiga RDB partition support for disks >= 2 TB

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Hi Michael.

Probably I was right with not submitting a patch myself. I´d likely 
would have been overwhelmed by the discussion and feedback :)

Michael Schmitz - 28.06.18, 06:58:
[…]
> >> In the interest of least surprises, we have to fix the 32 bit
> >> overflow (so we can even detect that it would have happened), and
> >> give the user the chance to carefully consider whether to accept
> >> the new behaviour. That means refusing to make available any
> >> partition that would have been affected by such overflow.
> > 
> > That is acceptable for me as I told before. Either mount or refuse
> > to
> > mount, but do not overflow and mount nonetheless :)
> > 
> > Mind you, I am not using my Amiga machines either at the moment. And
> > I repurposed the 2 TB disk years ago.
> 
> That's fine - I understand the 'profile' image was a true binary copy
> of the RDB, and placing that file at offset 0 in an image file is a
> legitimate use?

You actually ask me to remember about what that 'profile' image was? :)

Well, in the attachment note on the bug report I wrote: "should be just 
a binary copy", so I did not know exactly back then either. However the 
file starts with "RDSK" and then it has "PART" headers and so on. That 
looks pretty much like a binary copy of an RDB. I am a bit surprised by 
its small size of 2 KiB. But I see three partitions in there. According 
to the screenshot I also provided, the disk had three partitions. So 
probably Media Toolbox has been intelligent enough to just copy the used 
space of the reserved RDB area. Cause I think the reserved space must 
have been higher than 2 KiB. However the RDB/disk geometry editing 
screen does not display it and off hand I do not know where to look 
inside the RDB to see how much space has been reserved. Interestingly 
the "Total sectors" value in that Media Toolbox window also overflowed. 
But from my memory this was just a cosmetic issue in Media Toolbox. The 
"*.device" device drivers, the filesystems and the RDB handling code in 
AmigaOS do their own math. That is what NSD64 / TD64 was about.

https://bugzilla.kernel.org/show_bug.cgi?id=43511

> > I would not name the kernel option "eat_my_rdb", but use a less
> > dramatizing name.
> > 
> > Maybe just: "allow_64bit_rdb" or something like that.
> 
> I don't expect to get away with that :-)

Heh. :)

> > How does the user come to know about this kernel option? Will you
> > print its name in kernel log?
> 
> Depends on how easy we want to make it for users. If I put a BUG()
> trap with the check, the resulting log section will point to a
> specific line in block/partitions/amiga.c, from which the override
> option will be obvious. But that might be a little too opaque for
> some...

kernel-parameters.txt or mentioning in the warning would also be an 
option.

Thanks,
-- 
Martin





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