**NAME**

hashinit,hashdestroy,phashinit- manage kernel hash tables

**SYNOPSIS**

#include<sys/malloc.h>#include<sys/systm.h>#include<sys/queue.h>void*hashinit(intnelements,structmalloc_type*type,u_long*hashmask);voidhashdestroy(void*hashtbl,structmalloc_type*type,u_longhashmask);void*phashinit(intnelements,structmalloc_type*type,u_long*nentries);

**DESCRIPTION**

Thehashinit() andphashinit() functions allocate space for hash tables of size given by the argumentnelements. Thehashinit() function allocates hash tables that are sized to largest power of two less than or equal to argumentnelements. Thephashinit() function allocates hash tables that are sized to the largest prime number less than or equal to argumentnelements. 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 argumenttype. Thehashdestroy() function frees the space occupied by the hash table pointed to by argumenthashtbl. Argumenttypedetermines the malloc arena to use when freeing space. The argumenthashmaskshould be the bit mask returned by the call tohashinit() that allocated the hash table.

**IMPLEMENTATION** **NOTES**

The largest prime hash value chosen byphashinit() is 32749.

**RETURN** **VALUES**

Thehashinit() function returns a pointer to an allocated hash table and sets the location pointed to byhashmaskto the bit mask to be used for computing the correct slot in the hash table. Thephashinit() function returns a pointer to an allocated hash table and sets the location pointed to bynentriesto 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 infoomask. A subsequent call tohashdestroy() uses the value infoomask: ... hashdestroy(footable, M_FOO, foomask);

**DIAGNOSTICS**

Thehashinit() andphashinit() functions will panic if argumentnelementsis less than or equal to zero. Thehashdestroy() function will panic if the hash table pointed to byhashtblis not empty.

**SEE** **ALSO**

LIST_HEAD(3), malloc(9)

**BUGS**

There is nophashdestroy() function, and usinghashdestroy() to free a hash table allocated byphashinit() usually has grave consequences.