Looks like a bug in the 7300 disk driver
was-John McMillan
jcm at mtunb.ATT.COM
Tue Jan 10 07:35:07 AEST 1989
In article <813 at ttrde.UUCP> pfales at ttrde.UUCP (Peter Fales) writes:
>
>I have discovered what appears to be a bug in the hard disk device driver
>for the unix-pc.
...
It's a FEATURE, not a bug. Moreover, this feature will never be changed ;^}
Consider TAPE drives: in many systems, you can only communicate to the
drive in EVEN byte multiples -- unless things have changed in the last
twenty years since I've used a tape drive %v). Is this an error?
In the UNIX-PC, the RAW -- read that "character-device" -- interface
to the disk directly maps transfers into user RAM. Therefore, since
transfers to/from the disk are in 512 byte blocks, ya can only read
in 512-byte multiples.
In some other systems, boundary cases -- un-aligned first and last blocks
-- are read into kernel buffers and NOT into user-space. This permits
Peter's anticipated results.
Finally (fat chance of this ;-):
1) TSK-TSK -- users are NOT supposed to be accessing the RAW disk
at all. And if this is permitted... the special characteristics
of the RAW driver have to be coped with!
2) I believe I've seen this feature documented -- and isn't that
enough to satisfy everyone?
3) Lord[s], let us not descend into the hell of other groups that
have wasted untold kilo-bucks thrashing unresolvable differences
of opinion over system features -- not to mention address-to-index
computations by name.
PS: I haven't pursued the above issue through the source code so the above
drivel may be the first flawed argument of my life -- oops, I meant HOUR.
jc mcmillan -- att!mtunb!jcm -- just frothing for myself, not THEM.
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