Hello Christoph, Stefan I am wondering whether the problem occurred that value of BDRV_SECTOR_SIZE is a macro constant (defined at block.h). This problem could be fixed if we use variable instead of macro to implement BDRV_SECTOR_SIZE. Each block device may reassign the value if needed. Is it right??
Thanks a lot 2011/4/12 Christoph Hellwig <h...@lst.de> > On Sat, Apr 09, 2011 at 09:05:41PM +0100, Stefan Hajnoczi wrote: > > On Sat, Apr 9, 2011 at 5:51 PM, Lyu Mitnick <mitnick....@gmail.com> > wrote: > > > Hell all, > > > I have take a look of block/vpc.c and meet a question in > vpc_create().?At > > > the line > > > 550, the code is: > > > total_sectors = options->value.n / 512; > > > I am wondering whether the size between?total_sectors * 512 > > > and?options->value.n > > > would be discard. > > > > Yes, it rounds down. This reflects the assumption that a block device > > cannot be addressed below 512 byte sectors. Because of this block > > devices size must be a multiple of 512 bytes. > > > > I think a reasonable protection would be to have block.c:bdrv_create() > > fail if size is not a multiple of BDRV_SECTOR_SIZE. This way other > > image formats are protected too. > > There are block devices that aren't alignment to 512 bytes. Audio CDROMs > are > the most prominent example, or AS/400 disks. I don't think these matter > for > emulation, but if we'd ever implement DIF/DIX emulation inside qemu we'd > have to store the protection information somewhere. It still wouldn't > work with existing disk format, so adding the above check into the formats > bdrv_create routines sounds fine, but doing it in the core block code > might not be an overly smart idea. > > Mitnick
