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033a4603 30.\" $DragonFly: src/share/man/man9/hash.9,v 1.2 2004/06/28 02:57:11 drhodus Exp $
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31.\"
32.Dd May 14, 2004
33.Os
34.Dt HASH 9
35.Sh NAME
36.Nm hash ,
37.Nm hashinit ,
38.Nm phashinit
39.Nd generic hash table functions for the kernel
40.Sh SYNOPSIS
41.In sys/param.h
42.In sys/systm.h
43.In sys/malloc.h
44.Ft void *
45.Fn hashinit "int elements" "struct malloc_type *type" "u_long *hashmask"
46.Ft void *
47.Fn phashinit "int elements" "struct malloc_type *type" "u_long *nentries"
48.Sh DESCRIPTION
49The kernel hash functions are used for creating a generic hash table.
50.Pp
51The
52.Fn hashinit
53function returns a pointer to a hash table which is sized a
54.Dq "power of two"
55greater or equal to the number of
56.Fa elements
57requested.
58The masking value is stored in
59.Fa hashmask .
60.Pp
61The
62.Fn phashinit
63function returns a pointer to a prime number sized hash table.
64The number of
65.Fa elements
66requested is used to dictate an upper-bound for the size of the
67hash table.
68The final size of the hash table is stored by the function in
69.Fa nentries .
70.Pp
71The
72.Fa type
73argument to both of the above functions is used for keeping track
74of memory allocated for the hash table.
75See the
76.Xr malloc 9
77manual page for more information on memory statistics.
78.Sh CODE REFERENCES
79The VFS namecache code is one of many examples for using the
80.Fn hashinit
81function; it is located within the file
82.Pa sys/kern/vfs_cache.c .
83.Pp
84The hostcache code uses the
85.Fn phashinit
86function for creating a prime number sized hash table; it is located
87within the file
88.Pa sys/net/hostcache.c .
89.Pp
90All pathnames in this section are relative to the
91.Dx
92source tree.
93.Sh SEE ALSO
94.Xr tcp 4 ,
95.Xr udp 4 ,
96.Xr malloc 9 ,
97.Xr namei 9
98.Sh AUTHORS
99This manual page was written by
100.An Hiten Pandya Aq hmp@backplane.com .