Re: RFC: block size identification

[Patrick Leslie Polzer]

Hello Sven,

On Fri, 20 Jan 2006 01:51:47 +0100
Sven Luther <Sven Luther <address@hidden>> wrote:

 | There is another use-case of interest here. The amiga partition
 | table can keep information about the filesystems (sfs/pfs/affs
 | mostly) inside the individual partition block in the partition table,
 | among them the block size. Do you have some way of having this taking
 | in account ? Right now i reread the partition table from the
 | filesystem code to read in this information, which is hardly nice.
I'm note sure what you are trying to achieve.
To describe my patch in more detail:
The source files for every file system and disk label will contain
a static list of block sizes supported by the technology in question.

I understand that you have some redundant code in there, but that
cannot be avoided with my work.
But to remedy your problem you could employ some heuristics:

AFFS supports block sizes 2^{9..12}.
The root block is one block.
For every x in {9..12} check whether these conditions apply:

    [1] 2^x - 4 = ST.ROOT (where ST.ROOT is the number indicating
                           secondary type is root block)
    [2] ulong at 2^x - 12 = 0
    [3] ulong at 2^x - 16 = 0
    [4] ulong at 2^x - 48 = 0
    [5]  char at 2^x - 49 = 0

When this is true, 2^x is the block size of the file system.
When this is true for more than one x, fall back to the
partition table stuff.
All units in bytes.

I don't know how reliable [4] and [5] are -- these are reserved
fields.  Maybe [1] will suffice.

Some questions I'm interested in:

 * can Amiga FFS be used with non-Amiga disk labels?

 * why do Amiga file systems register fs{0..7}, e.g.
   affs0..7 in Parted?  Is this really necessary?
   Can't this be avoided?

 * what Amiga file system is the most popular
   today? Is AFFS still widely in use among Amiga users?
   What's the role of sfs and pfs?


Cheers,

Leslie

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