Tony Nelson wrote: > > The effect of the readahead bug is to prevent the last few dozen KB > > of the ISO from being read. I've done plenty of experiments. > You are confused. The read is not prevented, it only returns less > data than requested. Some badly written programs cannot deal with > that. > Checksumming can't deal with any of the extra data (it will compute > the checksum on the extra data as well). Reading the entire CD / DVD > and trimming it to the right size will work, provided you use > software that can accept a short read[1]. [1] <http://www.city-fan.org/tips/IsoImageFromMedia> Yes, if you read my original message, you'll see that I always use the rawread script for reading, which is referenced at the end of [1] as a better way of doing the same thing (since it can be used in a pipe instead of having to write the entire file to disk, as the isograb script does). My comments in bugs #186512 and #397141 (marked as a duplicate of #186512) describe how I experience the premature read failure while using this script to do the reading. Mediacheck also fails with these discs (except when using the F7 installer's mediacheck). The fact that the read works properly with the original F7 kernel shows that the entire ISO is actually on the discs. This problem is not too hard to reproduce - take a CD-R, burn a ~650-700 MB ISO using wodim/cdrecord in the simplest possible way: wodim dev=/dev/cdrom file.iso which uses TAO mode by default, and if you try to read it using rawread in an optical drive which triggers the readahead bug (about half to two-thirds of the drives I've owned have this problem), you'll see the read errors less than about 150 KB from the end (roughly 1/4000-th of the entire image). My father also saw it with a F8 DVD bought online, so it's not limited to CDs. After explaining the problem to the vendor and asking for a replacement burned properly (with zero-padding), he just sent an identical disc with the same problem, so instead of trying again, we just read off everything except the last few dozen KB, used wget -c to download the rest (which even on dialup only took a few seconds), then burned our own disc using zero padding, which passed mediacheck.
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