Matthew Wilcox - 26.04.18, 04:57:
On Wed, Apr 25, 2018 at 10:30:29PM +0200, David Sterba wrote:
I had similar toughts some time ago while browsing the fs/
directory.
Access to the filesystem images can be reimplemented in FUSE, but
other than that, I don't think the in-kernel code would be missed.
It's hard to know how many users are there. I was curious eg. about
bfs, befs, coda or feevxfs, looked at the last commits and searched
around web if there are any mentions or user community. But as long
as there's somebody listed in MAINTAINERS, the above are not
candidates for moving to staging or deletion.
Yeah, it's pretty sad how few commits some of these filesystems have
had in recent years. One can argue that they're stable and don't need
to be fixed because they aren't broken, but I find it hard to believe
that any of them were better-implemented than ext2 which still sees
regular bugfixes.
Regarding affs there is a severe issue which is not in affs itself but
in the handling of Rigid Disk Block (RDB) partitions, the Amiga
partitioning standard, which is far more advanced than MBR: It overruns
for 2 TB or larger drives and then wraps over to the beginning of the
drive – I bet you can imagine what happens if you write to an area
larger than 2 TB. I learned this with an external 2TB RDB partitioned
harddisk back then, which I used for Sam440ep (a kind of successor for
old, classic Amiga hardware) backup + some Linux related stuff in
another partition.
Joanne Dow, a developer who developed hdwrench.library which HDToolBox
uses for partitioning in AmigaOS 3.5/3.9, provided a patch back then,
but never officially put it officially through upstreaming as I offered
to make a good description and upstream it through Jens Axboe.
I may take this as a reason to… actually follow through this time,
hopefully remembering all the details in order to provide a meaningful
patch description – but I think mostly I can do just careful copy and
paste. Even tough I believe Joanne Dow´s fix only fixed my bug report
43511, but not 43511 which is more about a safeguarding issue in case of
future overflows, I still think it would be good to go in in case affs +
RDB stays in their current places.
However, in case you move affs to staging, I may be less motivated to do
so, but then I suggest you also move RDB partitioning support to
staging, cause this is the one that is known to be dangerously badly for
2 TB or larger disks. And yeah, I admit I did not follow through with
having that patch upstreamed. Probably I did not want to be responsible
in case my description would not have been absolutely accurate or the
patch breaks something else. I do not have that 2 TB drive anymore and
don´t feel like setting one up in a suitable way in order to go about
this patch, but my testing back then was quite elaborate and I still
feel pretty confident about it.
I totally get your motivation, but I would find it somewhat sad to see
the filesystems you mentioned go into staging. However, as I just shown
clearly, for the user it may be better, cause there may be unfixed
dangerous bugs. FUSE might be an interesting approach, but I bet it will
not solve the maintenance issue. If there is no one maintaining it in
the kernel, I think its unlikely to find someone adapting it to be a
FUSE filesystem and maintaining it. And then I am not aware of FUSE
based partitioning support. (And I think think ideally we´d had a
microkernel and run all filesystems in userspace processes with a
defined set of privileges, but that is simply not Linux as it is.)
Partitions: Amiga RDB partition on 2 TB disk way too big, while OK in
AmigaOS 4.1
https://lkml.org/lkml/2012/6/17/6
Bug 43521 - Amiga RDB partitions: truncates miscalculated partition size
instead of refusing to use it
https://bugzilla.kernel.org/show_bug.cgi?id=43521
Bug 43511 - Partitions: Amiga RDB partition on 2 TB disk way too big,
while OK in AmigaOS 4.1
https://bugzilla.kernel.org/show_bug.cgi?id=43511
I forward the relevant mail of Joanne, in
https://bugzilla.kernel.org/show_bug.cgi?id=43511#c7
I even have the patch in diff format. And I just checked, the issue is
still unpatched as of 4.16.3.
---------- Weitergeleitete Nachricht ----------
Betreff: Re: Partitions: Amiga RDB partition on 2 TB disk way too big,
while OK in AmigaOS 4.1
Datum: Montag, 18. Juni 2012, 03:28:48 CEST
Von: jdow <jdow@xxxxxxxxxxxxx>
An: Martin Steigerwald <Martin@xxxxxxxxxxxx>
Kopie: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>, linux-
kernel@xxxxxxxxxxxxxxx, Jens Axboe <axboe@xxxxxxxxx>, linux-
m68k@xxxxxxxxxxxxxxx
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@xxxxxxxxxxxx> 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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-------------------------------------------------------------
[…]
As long as there's someone who can be pestered with bugs, I don't see
the need to push their baby out of the tree. I'm a bit more nervous
about hfsplus; if it has users and no maintainer, those users are at
risk.
Perhaps we could advertise on Craigslist or something ... maintainer
wanted for LTR.
