From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Martin Steigerwald To: Michael Schmitz Cc: Geert Uytterhoeven , Jens Axboe , jdow , linux-m68k , linux-block@vger.kernel.org Subject: Re: Subject: [PATCH RFC] block: fix Amiga RDB partition support for disks >= 2 TB Date: Fri, 29 Jun 2018 23:24:36 +0200 Message-ID: <2499668.52U9LxLmUp@merkaba> In-Reply-To: <76bf5b8d-6ee1-8e77-4c2a-e0b5a095992b@gmail.com> References: <20180627012421.80B8F24E094@nmr-admin> <76bf5b8d-6ee1-8e77-4c2a-e0b5a095992b@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" List-ID: Hi Michael. Michael Schmitz - 29.06.18, 11:07: > > But it's up to the person (which is not Linux) formatting the disk > > to > > not try to use > > it on systems that cannot handle it, and may destroy it. > >=20 > >>> Let me clarify: what exactly would the kernel option allow? When > >>> to use it?>>=20 > >> Whether to use it if safe (on Linux). But whatever Linux does > >> (after > >> this patch), access will go to the right area of the disk (as > >> specified by the RDB) so Linux won't any longer stomp on anything > >> that would have mattered to 32 bit disk drivers. So it really > >> should be safe.>=20 > > Personally, I see no reason to depend on a kernel option, if it is > > safe to use. Just use it. >=20 > So to recap - someone partitions a disk on AmigaOS 4.x, taking > advantage of the large block device support there. > Using that disk on AmigaOS 3.1, data loss ensues. Whether or not Linux > (patched) ever touched the disk has no impact on that outcome. I am not even completely sure about that. Frankly I have no idea what=20 would happen when using such a disk on AmigaOS 3.1 *without* NSDPatch or=20 TD64 support (I think you could patch AmigaOS 3.1 with 64 Bit support=20 already and some 3rd party harddisk controllers by Phase 5 hat TD64=20 support at that time already). Unless I try it, which I won=C2=B4t at the=20 moment, I=C2=B4d say the behaviour is largely undefined. But hey, undefined means it may just overwrite start overwriting from=20 the beginning of the disk beyond 32 bit. And I think that is quite=20 likely. It could also crash, but if its an overflow I don=C2=B4t think why = it=20 would crash. Anyway, I never tried this out. But in any way: This would happen or not happen no matter whether Linux=20 parsed the RDB or not. I still think that the native OS warning really does not hurt=E2=80=A6 but = I=C2=B4d=20 spare myself the kernel option. Having the warning without the kernel=20 option would be a compromise between being cautious and being bold :). Thanks, =2D-=20 Martin