Stefan, On 12/15/16 01:47, Stefan Haberland wrote: > Partitions that are not aligned to the blocksize of a device may cause > invalid I/O requests because the blocklayer cares only about alignment > within the partition when building requests on partitions. > > device > |--------4096--------|--------4096--------|--------4096--------| > partition offset 512byte > |-512-|--------4096--------|--------4096--------|--------4096--------| > > When reading/writing one 4k block of the partition this maps to > reading/writing with an offset of 512 byte of the device leading to > unaligned requests for the device which in turn may cause unexpected > behavior of the device driver. > > For DASD devices we have to translate the block number into a cylinder, > head, record format. The unaligned requests lead to wrong calculation > and therefore to misdirected I/O. In a "good" case this leads to I/O > errors because the underlying hardware detects the wrong addressing. > In a worst case scenario this might destroy data on the device. > > To prevent partitions that are not aligned to the physical blocksize > of a device check for the alignment in the blkpg_ioctl. > > Signed-off-by: Stefan Haberland <[email protected]> > --- > block/ioctl.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/block/ioctl.c b/block/ioctl.c > index 755119c..8b83afee 100644 > --- a/block/ioctl.c > +++ b/block/ioctl.c > @@ -45,6 +45,9 @@ static int blkpg_ioctl(struct block_device *bdev, struct > blkpg_ioctl_arg __user > || pstart < 0 || plength < 0 || partno > > 65535) > return -EINVAL; > } > + /* check if partition is aligned to blocksize */ > + if (p.start % bdev_physical_block_size(bdev) != 0)
sd.c ensures that the logical block size (sector size in sd.c) is a power of 2 between 512 and 4096. So you can use: if (p.start & (bdev_physical_block_size(bdev) - 1)) Or use div_u64_rem to avoid an error on 32 bits builds. Best regards. -- Damien Le Moal, Ph.D. Sr. Manager, System Software Research Group, Western Digital Corporation [email protected] (+81) 0466-98-3593 (ext. 513593) 1 kirihara-cho, Fujisawa, Kanagawa, 252-0888 Japan www.wdc.com, www.hgst.com
