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.Dd June 6, 2012
.Dt HASHINIT 9
.Os
.Sh NAME
.Nm hashinit ,
.Nm hashinit_ext ,
.Nm hashdestroy ,
.Nm phashinit ,
.Nm phashinit_ext
.Nd generic hash table functions for the kernel
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.In sys/malloc.h
.Ft void *
.Fn hashinit "int count" "struct malloc_type *type" "u_long *hashmask"
.Ft void *
.Fn hashinit_ext "int count" "size_t size" "struct malloc_type *type" "u_long *hashmask"
.Ft void
.Fn hashdestroy "void *hashtbl" "struct malloc_type *type" "u_long hashmask"
.Ft void *
.Fn phashinit "int count" "struct malloc_type *type" "u_long *nentries"
.Ft void *
.Fn phashinit_ext "int count" "size_t size" "struct malloc_type *type" "u_long *nentries"
.Sh DESCRIPTION
The kernel hash functions are used for creating a generic hash table.
.Pp
The
.Fn hashinit
function returns a pointer to a hash table which is sized a
.Dq "power of two"
greater or equal to the element
.Fa count
requested.
The masking value is stored in
.Fa hashmask .
.Pp
The
.Fn phashinit
function returns a pointer to a prime number sized hash table.
The element
.Fa count
requested is used to dictate an upper-bound for the size of the
hash table.
The final size of the hash table is stored by the function in
.Fa nentries .
.Pp
The
.Fa type
argument to both of the above functions is used for keeping track
of memory allocated for the hash table.
See the
.Xr kmalloc 9
manual page for more information on memory statistics.
.Pp
The
.Fn hashinit_ext
and
.Fn phashinit_ext
functions are extended versions of
.Fn hashinit
and
.Fn phashinit
which take the
.Fa size
of the structure as an additional argument and will zero the array instead
of assuming that it is an array of
.Dv LIST_HEAD Ns s .
.Pp
The
.Fn hashdestroy
function frees the space occupied by the hash table pointed to by argument
.Fa hashtbl .
Argument
.Fa type
determines the malloc arena to use when freeing space.
The argument
.Fa hashmask
should be the bit mask returned by the call to
.Fn hashinit
that allocated the hash table.
The argument
.Fa flags
must be used with one of the following values.
.Sh SEE ALSO
.Xr tcp 4 ,
.Xr udp 4 ,
.Xr kmalloc 9 ,
.Xr nlookup 9
.Sh AUTHORS
This manual page was written by
.An Hiten Pandya Aq Mt hmp@backplane.com .
.Sh BUGS
There is no
.Fn phashdestroy
function, and using
.Fn hashdestroy
to free a hash table allocated by
.Fn phashinit
usually has grave consequences.