xref: /dragonfly/lib/libc/db/man/mpool.3 (revision 0bb9290e) 
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28.\"	@(#)mpool.3	8.1 (Berkeley) 6/4/93
29.\" $FreeBSD: src/lib/libc/db/man/mpool.3,v 1.5.2.5 2003/02/23 19:45:52 trhodes Exp $
30.\" $DragonFly: src/lib/libc/db/man/mpool.3,v 1.3 2005/09/19 09:20:37 asmodai Exp $
31.\"
32.Dd June 4, 1993
33.Dt MPOOL 3
34.Os
35.Sh NAME
36.Nm mpool
37.Nd "shared memory buffer pool"
38.Sh SYNOPSIS
39.In db.h
40.In mpool.h
41.Ft MPOOL *
42.Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache"
43.Ft void
44.Fo mpool_filter
45.Fa "MPOOL *mp"
46.Fa "void (*pgin)(void *, pgno_t, void *)"
47.Fa "void (*pgout)(void *, pgno_t, void *)"
48.Fa "void *pgcookie"
49.Fc
50.Ft void *
51.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr"
52.Ft void *
53.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags"
54.Ft int
55.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags"
56.Ft int
57.Fn mpool_sync "MPOOL *mp"
58.Ft int
59.Fn mpool_close "MPOOL *mp"
60.Sh DESCRIPTION
61The
62.Nm mpool
63library interface is intended to provide page oriented buffer management
64of files.
65The buffers may be shared between processes.
66.Pp
67The
68.Fn mpool_open
69function initializes a memory pool.
70The
71.Fa key
72argument is the byte string used to negotiate between multiple
73processes wishing to share buffers.
74If the file buffers are mapped in shared memory, all processes using
75the same key will share the buffers.
76If
77.Fa key
78is
79.Dv NULL ,
80the buffers are mapped into private memory.
81The
82.Fa fd
83argument is a file descriptor for the underlying file, which must be seekable.
84If
85.Fa key
86is
87.No non\- Ns Dv NULL
88and matches a file already being mapped, the
89.Fa fd
90argument is ignored.
91.Pp
92The
93.Fa pagesize
94argument is the size, in bytes, of the pages into which the file is broken up.
95The
96.Fa maxcache
97argument is the maximum number of pages from the underlying file to cache
98at any one time.
99This value is not relative to the number of processes which share a file's
100buffers, but will be the largest value specified by any of the processes
101sharing the file.
102.Pp
103The
104.Fn mpool_filter
105function is intended to make transparent input and output processing of the
106pages possible.
107If the
108.Fa pgin
109function is specified, it is called each time a buffer is read into the memory
110pool from the backing file.
111If the
112.Fa pgout
113function is specified, it is called each time a buffer is written into the
114backing file.
115Both functions are called with the
116.Fa pgcookie
117pointer, the page number and a pointer to the page to being read or written.
118.Pp
119The
120.Fn mpool_new
121function takes an
122.Ft MPOOL
123pointer and an address as arguments.
124If a new page can be allocated, a pointer to the page is returned and
125the page number is stored into the
126.Fa pgnoaddr
127address.
128Otherwise,
129.Dv NULL
130is returned and
131.Va errno
132is set.
133.Pp
134The
135.Fn mpool_get
136function takes a
137.Ft MPOOL
138pointer and a page number as arguments.
139If the page exists, a pointer to the page is returned.
140Otherwise,
141.Dv NULL
142is returned and
143.Va errno
144is set.
145The
146.Fa flags
147argument is not currently used.
148.Pp
149The
150.Fn mpool_put
151function unpins the page referenced by
152.Fa pgaddr .
153The
154.Fa pgaddr
155argument
156must be an address previously returned by
157.Fn mpool_get
158or
159.Fn mpool_new .
160The
161.Fa flags
162argument is specified by
163.Em or Ns 'ing
164any of the following values:
165.Bl -tag -width indent
166.It Dv MPOOL_DIRTY
167The page has been modified and needs to be written to the backing file.
168.El
169.Pp
170The
171.Fn mpool_put
172function
173returns 0 on success and -1 if an error occurs.
174.Pp
175The
176.Fn mpool_sync
177function writes all modified pages associated with the
178.Ft MPOOL
179pointer to the
180backing file.
181The
182.Fn mpool_sync
183function
184returns 0 on success and -1 if an error occurs.
185.Pp
186The
187.Fn mpool_close
188function free's up any allocated memory associated with the memory pool
189cookie.
190Modified pages are
191.Em not
192written to the backing file.
193The
194.Fn mpool_close
195function
196returns 0 on success and -1 if an error occurs.
197.Sh ERRORS
198The
199.Fn mpool_open
200function may fail and set
201.Va errno
202for any of the errors specified for the library routine
203.Xr malloc 3 .
204.Pp
205The
206.Fn mpool_get
207function may fail and set
208.Va errno
209for the following:
210.Bl -tag -width Er
211.It Bq Er EINVAL
212The requested record doesn't exist.
213.El
214.Pp
215The
216.Fn mpool_new
217and
218.Fn mpool_get
219functions may fail and set
220.Va errno
221for any of the errors specified for the library routines
222.Xr read 2 ,
223.Xr write 2 ,
224and
225.Xr malloc 3 .
226.Pp
227The
228.Fn mpool_sync
229function may fail and set
230.Va errno
231for any of the errors specified for the library routine
232.Xr write 2 .
233.Pp
234The
235.Fn mpool_close
236function may fail and set
237.Va errno
238for any of the errors specified for the library routine
239.Xr free 3 .
240.Sh SEE ALSO
241.Xr btree 3 ,
242.Xr dbopen 3 ,
243.Xr hash 3 ,
244.Xr recno 3
245