Re: [Freedos-kernel] EXT3 support

[H. Peter Anvin]

On August 26, 2016 12:26:52 AM PDT, Eric Auer  wrote:
>
>Hi HPA! The boot sector takes a BIOS drive number of the
>to-be-booted drive from the MBR, which can take it from
>the BIOS. There also are patches to take the MBR item by
>pointer from the MBR, but those are not used by default.
>
>So I guess the kernel could take the drive number from a
>boot sector, which at the moment is easy because the boot
>sector stores the value from the MBR in the drive byte of
>the boot sector loaded into RAM, which is a predictable
>location in general. Might be fun for booting from 0x81.
>
>>> support for EXT3 in the kernel would indeed be large/complex.
>
>Would not do that, but would boot DOS by MEMDISK and load a
>full EXT3 driver from there later :-) Same for ISO9660, but
>there "read files from ISO root dir" might be quite small,
>so boot without MEMDISK might be interesting as well...
>
>>> Regarding the idea to have the kernel "natively boot from a
>>> RAMDISK in HIGH MEMORY which would NOT be A: or C: ... Well,
>>> on modern computers it should not be a problem to "hog" the
>>> drive letter of the A: floppy drive - you probably have at
>>> most ONE real floppy next to that ramdisk anyway and letter
>>> B: is still free :-) So in that sense, MEMDISK is ok for me.
>
>Exactly :-)
>
>> So this is a horribly stale discussion, but it seems that all that is
>> needed is the ability to hide somewhere a preferred drive letter for
>the
>> FreeDOS kernel to pick up and use.  It is trivial to add support for
>> passing such information along in MEMDISK.
>> 
>>  -hpa

Hi!

Memdisk already supports being a disk number other than 0x00 or 0x80, and the 
DL register will reflect that.  However, I was thinking of provided a more 
explicit hint, so that scripts can reply on the ramdisk being, say, R:
-- 
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Re: [Freedos-kernel] EXT3 support

[Eric Auer]

Hi HPA! The boot sector takes a BIOS drive number of the
to-be-booted drive from the MBR, which can take it from
the BIOS. There also are patches to take the MBR item by
pointer from the MBR, but those are not used by default.

So I guess the kernel could take the drive number from a
boot sector, which at the moment is easy because the boot
sector stores the value from the MBR in the drive byte of
the boot sector loaded into RAM, which is a predictable
location in general. Might be fun for booting from 0x81.

>> support for EXT3 in the kernel would indeed be large/complex.

Would not do that, but would boot DOS by MEMDISK and load a
full EXT3 driver from there later :-) Same for ISO9660, but
there "read files from ISO root dir" might be quite small,
so boot without MEMDISK might be interesting as well...

>> Regarding the idea to have the kernel "natively boot from a
>> RAMDISK in HIGH MEMORY which would NOT be A: or C: ... Well,
>> on modern computers it should not be a problem to "hog" the
>> drive letter of the A: floppy drive - you probably have at
>> most ONE real floppy next to that ramdisk anyway and letter
>> B: is still free :-) So in that sense, MEMDISK is ok for me.

Exactly :-)

> So this is a horribly stale discussion, but it seems that all that is
> needed is the ability to hide somewhere a preferred drive letter for the
> FreeDOS kernel to pick up and use.  It is trivial to add support for
> passing such information along in MEMDISK.
> 
>   -hpa



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