VBLKSIZE
if (nb > VBLKSIZE / DEV_BSIZE)
nb = VBLKSIZE / DEV_BSIZE;
if (n > VBLKSIZE)
n = VBLKSIZE;
#define VBLKMASK (VBLKSIZE - 1)
#define DBPERVBLK (VBLKSIZE / DEV_BSIZE)
((off) / VBLKSIZE) * DBPERVBLK)
char blkbuf[VBLKSIZE]; /* filesystem blocks */
char indbuf[VBLKSIZE]; /* indir blocks */