[iyonix-support] Re: Bugs in SCSIFS?
- From: Kade Hansson <kade.hansson@xxxxxxxxxxxxxxxx>
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Mon, 25 Jun 2007 11:02:12 +1000
Dave Higton wrote:
Presumably it would be possible to plug in a drive formatted to
ext2, ext3, reiserfs, or whatever, and RISC OS should be able
to read and write it. Whether that's of any use to anybody is
another matter.
One other thing: I think it's time we appropriated a partition
type code for RISC OS.
Perhaps, but you do know that RISC OS FileCore/ADFS (to be referred to
just as ADFS from here on out) traditionally does not use DOS-style
partition tables. Instead, ADFS assumes that the first partition of a
disc is its own. (Or if not, it passes it around for things like DOSFS
to claim.) A trick that BSD and Linux use is that the (actually two)
sector space immediately beyond the limit of that partition, if it is
FileCore, is assumed to be a partition table (a so-called "RISC OS
partition table,"* but it was invented for BSD and Linux)- though like
no other you have ever seen. This is because you can't actually assume
it is a partition table: it may be garbage, another partition or outside
LBA space entirely (as is the case with a drive with just a FileCore
partition.) Therefore it uses magic values like 0D05D15C (DOSDisc) and
F11EC05E (FileCore) to label the partition types. Naturally ADFS already
has a code in this scheme, although traditionally ADFS can only read the
first partition, because it doesn't know about this scheme either.
* Many of the IDEFS and SCSIFS implementations from third parties also
have their own incompatible partition schemes. But as we are talking
Acorn's implementation here, I think it is best to ignore these.
If a RISC OS partition is to share with ext2/ext3 or FAT discs, I would
suggest that the disc must be formatted in the BSD or Linux way (as I
have just described), as this is the only way FileCore can recognise the
disc as its own. It would then be possible for a module (such as the one
I gather you are planning to write) to use FileCore to read beyond the
disc limit (provide your own disc record) and give a filing system view
on the additional partitions, just as IscaFS does. This does not
interfere with the assumptions ADFS makes, and allows both to coexist in
harmony without the need to rejig ADFS.
One problem with this approach is that Windows and other devices with
proprietary FAT drivers, like MP3 players and cameras, will not be able
to see the FAT partition. But unless we want to muck around with the
ADFS code, that is probably the only approach to FileCore sharing a disc
with FAT. The advantage is that BSD and Linux will be able to work the
disc out, and an increasingly many embedded devices are using Linux, so
there is a (admittedly slim) chance this may all work out of the box.
Good luck with your mission, should you decide to accept it,
Archer
End.
---
To alter your preferences or leave the group,
visit //www.freelists.org/list/iyonix-support
Other info via //www.freelists.org/webpage/iyonix-support
Other related posts:
