Allan Streib <astr...@indiana.edu> wrote:
> Seems like one of those numbers that was chosen long ago, when disks
> had orders of magnitude less storage capacity they have now, and 16
> partitions really would have been more than enough.
the word "chosen" makes it seem like such an arbitrary decision.
As currently written, the partition table must fit in a single sector.
Read disklabel.h and figure out how this part works:
struct partition { /* the partition table */
u_int32_t p_size; /* number of sectors (low part) */
u_int32_t p_offset; /* starting sector (low part) */
u_int16_t p_offseth; /* starting sector (high part) */
u_int16_t p_sizeh; /* number of sectors (high part) */
u_int8_t p_fstype; /* filesystem type, see below */
u_int8_t p_fragblock; /* encoded filesystem frag/block */
u_int16_t p_cpg; /* UFS: FS cylinders per group */
} d_partitions[MAXPARTITIONS]; /* actually may be more */
...
#define DL_GETDSIZE(d) (((u_int64_t)(d)->d_secperunith << 32) + \
(d)->d_secperunit)
#define DL_SETDSIZE(d, n) do { \
u_int64_t x = (n); \
(d)->d_secperunith = x >> 32; \
(d)->d_secperunit = x; \
} while (0)
#define DL_GETBSTART(d) (((u_int64_t)(d)->d_bstarth << 32) + \
(d)->d_bstart)
#define DL_SETBSTART(d, n) do { \
u_int64_t x = (n); \
(d)->d_bstarth = x >> 32; \
(d)->d_bstart = x; \
} while (0)
etc etc etc
Long time ago, it was chosen that cars should have 4 wheels.
