Arnd Bergmann wrote: > On Wednesday 18 July 2007, Gerd Hoffmann wrote: > >> Rusty Russell wrote: >> >>> You mean backend? For networking it makes a great deal of sense. For >>> block it makes far less sense (COW, weird formats, etc). >>> >> For block you probably want both: userspace driver which can handle all >> sorts of funny image files, and a kernel driver doing a 1:1 mapping to a >> block device (lvm volume). >> >> > > Interestingly, once you have the kernel driver that maps a block device, > you can do most of the useful user scenarios by means of /dev/loop > and/or device mapper. >
Not quite. Using device mapper to implement something like qcow turns out to be pretty painful. qcow, for instance, doesn't guarantee that blocks will be aligned to a sector boundary. It also doesn't guarantee that blocks are >= PAGE_SIZE. The other problem is that device mapper doesn't very much like to have very large tables so you end up having to use the table as a cache. See dm-userspace for an actual implementation of all of this. I'm beginning to think that a more proper userspace block device would be interesting. http://wiki.xensource.com/xenwiki/DmUserspace Regards, Anthony Liguori > Arnd <>< > > ------------------------------------------------------------------------- > This SF.net email is sponsored by DB2 Express > Download DB2 Express C - the FREE version of DB2 express and take > control of your XML. No limits. Just data. Click to get it now. > http://sourceforge.net/powerbar/db2/ > _______________________________________________ > kvm-devel mailing list > kvm-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/kvm-devel > > ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
