On Wed, 29 Mar 2006 14:26:26 -0500 Peter Jones <pjones@xxxxxxxxxx> wrote: > On Wed, 2006-03-29 at 19:51 +0200, Rob van Nieuwkerk wrote: > > > Sure. Or something like this: > > > > dd conv=idirect if=/dev/cdrom count=right_number | sha1sum > > > > And if the dd used on the FC ISO does not support the O_DIRECT feature, > > just add it. Or write a completely trivial 10 line C program that > > does the same. > > This will almost always get you the wrong result. At the very least, > you need 'bs=2048 count="$(($(isosize /dev/cdrom) / 2048))"' with that, > or you wind up doing md5sum on completely bogus data with some media. > > But as it turns out, that fails the exact same way that mediacheck does. > > > I really never understood why there never has been any trivial > > work-around on the FC images for this very annoying problem. > > dd does read(2) just like mediacheck does. There isn't some spooky > magic here. It fails in exactly the same ways for exactly the same > reasons. Hi Peter, Did you miss the O_DIRECT part ? A read(2) on an fd opened with O_DIRECT should never lead to any readahead by the kernel. On the device level *only* the blocks requested by the userspace read() are read. Nothing more. greetings, Rob van Nieuwkerk -- fedora-devel-list mailing list fedora-devel-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-devel-list
