HASHINIT (9) | Kernel routines | Unix Manual Pages | :man|

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HASHINIT (9) \| Kernel routines \| Unix Manual Pages \| :man▋ NAME hashinit, hashdestroy, phashinit - manage kernel hash tables CONTENTS Synopsis Description Implementation Notes Return Values Examples Diagnostics See Also Bugs SYNOPSIS .In sys/malloc.h .In sys/systm.h .In sys/queue.h "void "* `hashinit "int nelements" "struct malloc_type type" "u_long hashmask"` void `hashdestroy "void hashtbl" "struct malloc_type type" "u_long hashmask"` "void "* `phashinit "int nelements" "struct malloc_type type" "u_long nentries"` DESCRIPTION The `hashinit` and `phashinit` functions allocate space for hash tables of size given by the argument nelements. The `hashinit` function allocates hash tables that are sized to largest power of two less than or equal to argument nelements. The `phashinit` function allocates hash tables that are sized to the largest prime number less than or equal to argument nelements. Allocated hash tables are contiguous arrays of LIST_HEAD(3) entries, allocated using malloc(9), and initialized using LIST_INIT(3). The malloc arena to be used for allocation is pointed to by argument type. The `hashdestroy` function frees the space occupied by the hash table pointed to by argument hashtbl. Argument type determines the malloc arena to use when freeing space. The argument hashmask should be the bit mask returned by the call to `hashinit` that allocated the hash table. IMPLEMENTATION NOTES The largest prime hash value chosen by `phashinit` is 32749. RETURN VALUES The `hashinit` function returns a pointer to an allocated hash table and sets the location pointed to by hashmask to the bit mask to be used for computing the correct slot in the hash table. The `phashinit` function returns a pointer to an allocated hash table and sets the location pointed to by nentries to the number of rows in the hash table. EXAMPLES A typical example is shown below: ... static LIST_HEAD(foo, foo) footable; static u_long foomask; ... footable = hashinit(32, M_FOO, &foomask); Here we allocate a hash table with 32 entries from the malloc arena pointed to by `M_FOO`. The mask for the allocated hash table is returned in foomask. A subsequent call to `hashdestroy` uses the value in foomask: ... hashdestroy(footable, M_FOO, foomask); DIAGNOSTICS The `hashinit` and `phashinit` functions will panic if argument nelements* is less than or equal to zero. The `hashdestroy` function will panic if the hash table pointed to by hashtbl is not empty. SEE ALSO LIST_HEAD(3), malloc(9) BUGS

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