SWB_DMMAX
j = ((blk + SWB_DMMAX) & ~SWB_DMMASK) - blk;
#define BLK2DEVIDX(blk) (nswdev > 1 ? blk / SWB_DMMAX % nswdev : 0)
#define SWB_DMMASK (SWB_DMMAX - 1)
off = blkno % SWB_DMMAX;
if (off + sz > SWB_DMMAX) {
seg = blkno / SWB_DMMAX;
nbio->bio_offset = (off_t)(seg * SWB_DMMAX + off) << PAGE_SHIFT;
for (dvbase = SWB_DMMAX; dvbase < aligned_nblks; dvbase += SWB_DMMAX) {
blk = min(aligned_nblks - dvbase, SWB_DMMAX);
vsbase = index * SWB_DMMAX + dvbase * nswdev;
for (dvbase = SWB_DMMAX; dvbase < aligned_nblks; dvbase += SWB_DMMAX) {
blk = min(aligned_nblks - dvbase, SWB_DMMAX);
vsbase = index * SWB_DMMAX + dvbase * nswdev;
seg = base / SWB_DMMAX;