checking sh1asum of Fedora Core 6 Installation DVD without boot

[Paul Howarth]

Tim wrote:
> Paul Howarth:
>>>> Your file may have extra bytes appended to the end of it because the 
>>>> kernel does not detect the end of the written data
> 
> Tim:
>>> That's the second fault related to checking install discs that ought to
>>> get fixed, rather than worked around.  Hasn't anybody worked out why it
>>> doesn't do it correctly?
> 
> Paul Howarth:
>> It's the same fault, namely the kernel returning too much data on some 
>> hardware. If it was an easy fix, I'm sure it would have been done by now.
> 
> It and the DMA fault are the same thing?  But anyway, this would beg the
> question:  Does it ever manage to read from the drive properly?  (Post
> installation.)

The underlying problem is that the kernel doesn't detect the end of the 
written data correctly. This may or may not be a DMA issue (turning off 
DMA doesn't always fix the problem). An effect of this is returning 
excess data on some hardware when reading the entire contents of the 
media, which in turn causes media check errors because the excess data 
is not included in the checksum.

During normal operation there is no problem because there is a 
filesystem on the media and the filesystem indicates how much data there 
is on the media, so no attempt is ever made to read until "end of media" 
is reached; and the right amount of data is always requested via the 
filesystem layer.

Hence Alan Cox's advice to ignore mediacheck.

Paul.