FFS is limited to 2 GHz file size if you don't want any corruption using
fseek(). Otherwise it can go to 4 GHz sort of safely.
{^_^}
On 20180627 00:57, Martin Steigerwald wrote:
Michael Schmitz - 27.06.18, 03:07:
Joanne,
As far as I have been able to test, the change is backwards compatible
(RDB partitions from an old disk 80 GB disk are still recognized OK).
That"s only been done on an emulator though.
Your advice about the dangers of using RDB disks that would have
failed the current Linux RDB parser on legacy 32 bit systems is well
taken though. Maybe Martin can clarify that for me - was the 2 TB disk
in question ever used on a 32 bit Amiga system?
Sure! Are there actually *any* 64 bit Amiga systems? I am not completely
sure architecture-wise, but the operating system is still just 32-Bit.
However, on AmigaOS officially since at least 3.5/3.9 there are various
mechanisms to handle 64-bit block numbers for disk devices, called
NSD64, TD64 and scsi direct¹. One of them, NSD 64 in AmigaOS 3.5/3.9, is
part of the operating system. First via SetPatch based update to
Kickstart ROM, but with AmigaOS 4.x its just included.
[1] http://www.amigawiki.de/doku.php?id=de:system:filesystems_limits
(I do not agree with maximum filesystem size limits stated there for
Amiga Fast Filesystem (FFS), but well, for early FFS versions they could
have been true, I am pretty sure that at least with higher block sizes
you can have FFS > 2 GiB in size. And I remember having had JFXS and I
think also SFS2 partitions in AmigaOS 4 with more than 100 GiB.)
RDB disk format is meant for legacy use only, so I think we can get
away with printing a big fat warning during boot, advising the user
that the oversize RDB partition(s) scanned are not compatible with
legacy 32 bit AmigaOS. With the proposed fix they will work under both
AmigaOS 4.1 and Linux instead of truncating the first overflowing
partition at disk end and trashing valid partitions that overlap,
which is what Martin was after.
They are compatible. For AmigaOS 4.x I am completely sure, cause I
installed and used the disk there. That was the original motivation for
my Linux bug report back then: I used the disk in AmigaOS 4 *just fine*
and it broke in Linux. I used Media Toolbox in order to create the RDB I
posted back then.
Its difficult to find proof for my claims online, but here is an
official one:
http://wiki.amigaos.net/wiki/RDB
Limits of filesystem sizes may of course be different, but here we are
talking about RDB.
Also this confirms that RDB only uses 512 byte block size on AmigaOS 4.
Hmmm, I even created the page back then. Interestingly at about the same
time I made the bug report about the Linux issue. The calculations in
there are not really from me. I bet I copied them over from what other
AmigaOS developers wrote on development mailing lists, at that time.
With their agreement. I think I started my research back then due by my
own question on: Will such a large disk actually work in AmigaOS?
It is all a long time ago…
If that still seems too risky, we can make the default behaviour to
bail out once a potential overflow is detected, and allow the user to
override that through a boot parameter. I'd leave that decision up for
the code review on linux-block.
Two more comments: Linux uses 512 byte block sizes for the partition
start and size calculations, so a change of the RDB blocksize to
reduce the block counts stored in the RDB would still result in the
same overflow. And amiga-fdisk is indeed utterly broken and needs
updating (along with probably most legacy m68k partitioners). Adrian
has advertised parted as replacement for the old tools - maybe this
would make a nice test case for parted?
I always used AmigaOS based tools to partition in RDB format, cause I
never trusted amiga-fdisk :).
On Tue, Jun 26, 2018 at 9:45 PM, jdow <j...@earthlink.net> wrote:
If it is not backwards compatible I for one would refuse to use it.
And if it still mattered that much to me I'd also generate a
reasonable alternative. Modifying RDBs nay not be even an
approximation of a good idea. You'd discover that as soon as an RDB
uint64_t disk is tasted by a uint32_t only system. If it is for
your personal use then you're entirely free to reject my advice and
are probably smart enough to keep it working for yourself.
GPT is probably the right way to go. Preserve the ability to read
RDBs for legacy disks only.
{^_^}
On 20180626 01:31, Michael Schmitz wrote:
Joanne,
I think we all agree that doing 32 bit calculations on 512-byte
block
addresses that overflow on disks 2 TB and larger is a bug, causing
the issues Martin reported. Your patch addresses that by using the
correct data type for the calculations (as do other partition
parsers that may have to deal with large disks) and fixes Martin's
bug, so appears to be the right thing to do.
Using 64 bit data types for disks smaller than 2 TB where
calculations don't currently overflow is not expected to cause new
issues, other than enabling use of disk and partitions larger than
2 TB (which may have ramifications with filesystems on these
partitions). So comptibility is preserved.
Forcing larger block sizes might be a good strategy to avoid
overflow
issues in filesystems as well, but I can't see how the block size
stored in the RDB would enforce use of the same block size in
filesystems. We'll have to rely on the filesystem tools to get
that right, too. Linux AFFS does allow block sizes up to 4k (VFS
limitation) so this should allow partitions larger than 2 TB to
work already (but I suspect Al Viro may have found a few issues
when he looked at the AFFS code so I won't say more). Anyway
partitioning tools and filesystems are unrelated to the Linux
partition parser code which is all we aim to fix in this patch.
If you feel strongly about unknown ramifications of any filesystems
on partitions larger than 2 TB, say so and I'll have the kernel
print a warning about these partitions.
I'll get this patch tested on Martin's test case image as well as
on a RDB image from a disk known to currently work under Linux
(thanks Geert for the losetup hint). Can't do much more without
procuring a working Amiga disk image to use with an emulator,
sorry. The Amiga I plan to use for tests is a long way away from
my home indeed.
Cheers,
Michael
Am 26.06.18 um 17:17 schrieb jdow:
As long as it preserves compatibility it should be OK, I suppose.
Personally I'd make any partitioning tool front end gently force
the
block size towards 8k as the disk size gets larger. The file
systems
may also run into 2TB issues that are not obvious. An unused
blocks
list will have to go beyond a uint32_t size, for example. But a
block
list (OFS for sure, don't remember for the newer AFS) uses a tad
under 1% of the disk all by itself. A block bitmap is not quite
so bad. {^_-}
Just be sure you are aware of all the ramifications when you make
a
change. I remember thinking about this for awhile and then
determining I REALLY did not want to think about it as my brain
was getting tied into a gordian knot.
{^_^}
On 20180625 19:23, Michael Schmitz wrote:
Joanne,
Martin's boot log (including your patch) says:
Jun 19 21:19:09 merkaba kernel: [ 7891.843284] sdb: RDSK (512)
sdb1
(LNX^@)(res 2 spb 1) sdb2 (JXF^D)(res 2 spb 1) sdb3 (DOS^C)(res 2
spb
4)
Jun 19 21:19:09 merkaba kernel: [ 7891.844055] sd 7:0:0:0: [sdb]
Attached SCSI disk
so it's indeed a case of self inflicted damage (RDSK (512) means
512
byte blocks) and can be worked around by using a different block
size.
Your memory serves right indeed - blocksize is in 512 bytes
units.
I'll still submit a patch to Jens anyway as this may bite others
yet.
Cheers,
Michael
On Sun, Jun 24, 2018 at 11:40 PM, jdow <j...@earthlink.net>
wrote:
BTW - anybody who uses 512 byte blocks with an Amiga file system
is
a famn
dool.
If memory serves the RDBs think in blocks rather than bytes so
it
should
work up to 2 gigablocks whatever your block size is. 512 blocks
is
2199023255552 bytes. But that wastes just a WHOLE LOT of disk in
block maps.
Go up to 4096 or 8192. The latter is 35 TB.
{^_^}
On 20180624 02:06, Martin Steigerwald wrote:
Hi.
Michael Schmitz - 27.04.18, 04:11:
test results at
https://bugzilla.kernel.org/show_bug.cgi?id=43511
indicate the RDB parser bug is fixed by the patch given there,
so if
Martin now submits the patch, all should be well?
Ok, better be honest than having anyone waiting for it:
I do not care enough about this, in order to motivate myself
preparing the a patch from Joanne Dow´s fix.
I am not even using my Amiga boxes anymore, not even the
Sam440ep
which
I still have in my apartment.
So RDB support in Linux it remains broken for disks larger 2
TB,
unless
someone else does.
Thanks.
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