xref: /dragonfly/lib/libc/db/man/mpool.3 (revision 7bc7e232) 
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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 1.5 2007/08/18 20:48:47 swildner 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 LIBRARY
39.Lb libc
40.Sh SYNOPSIS
41.In db.h
42.In mpool.h
43.Ft MPOOL *
44.Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache"
45.Ft void
46.Fo mpool_filter
47.Fa "MPOOL *mp"
48.Fa "void (*pgin)(void *, pgno_t, void *)"
49.Fa "void (*pgout)(void *, pgno_t, void *)"
50.Fa "void *pgcookie"
51.Fc
52.Ft void *
53.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr"
54.Ft void *
55.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags"
56.Ft int
57.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags"
58.Ft int
59.Fn mpool_sync "MPOOL *mp"
60.Ft int
61.Fn mpool_close "MPOOL *mp"
62.Sh DESCRIPTION
63The
64.Nm
65library interface is intended to provide page oriented buffer management
66of files.
67The buffers may be shared between processes.
68.Pp
69The
70.Fn mpool_open
71function initializes a memory pool.
72The
73.Fa key
74argument is the byte string used to negotiate between multiple
75processes wishing to share buffers.
76If the file buffers are mapped in shared memory, all processes using
77the same key will share the buffers.
78If
79.Fa key
80is
81.Dv NULL ,
82the buffers are mapped into private memory.
83The
84.Fa fd
85argument is a file descriptor for the underlying file, which must be seekable.
86If
87.Fa key
88is
89.No non\- Ns Dv NULL
90and matches a file already being mapped, the
91.Fa fd
92argument is ignored.
93.Pp
94The
95.Fa pagesize
96argument is the size, in bytes, of the pages into which the file is broken up.
97The
98.Fa maxcache
99argument is the maximum number of pages from the underlying file to cache
100at any one time.
101This value is not relative to the number of processes which share a file's
102buffers, but will be the largest value specified by any of the processes
103sharing the file.
104.Pp
105The
106.Fn mpool_filter
107function is intended to make transparent input and output processing of the
108pages possible.
109If the
110.Fa pgin
111function is specified, it is called each time a buffer is read into the memory
112pool from the backing file.
113If the
114.Fa pgout
115function is specified, it is called each time a buffer is written into the
116backing file.
117Both functions are called with the
118.Fa pgcookie
119pointer, the page number and a pointer to the page to being read or written.
120.Pp
121The
122.Fn mpool_new
123function takes an
124.Ft MPOOL
125pointer and an address as arguments.
126If a new page can be allocated, a pointer to the page is returned and
127the page number is stored into the
128.Fa pgnoaddr
129address.
130Otherwise,
131.Dv NULL
132is returned and
133.Va errno
134is set.
135.Pp
136The
137.Fn mpool_get
138function takes a
139.Ft MPOOL
140pointer and a page number as arguments.
141If the page exists, a pointer to the page is returned.
142Otherwise,
143.Dv NULL
144is returned and
145.Va errno
146is set.
147The
148.Fa flags
149argument is not currently used.
150.Pp
151The
152.Fn mpool_put
153function unpins the page referenced by
154.Fa pgaddr .
155The
156.Fa pgaddr
157argument
158must be an address previously returned by
159.Fn mpool_get
160or
161.Fn mpool_new .
162The
163.Fa flags
164argument is specified by
165.Em or Ns 'ing
166any of the following values:
167.Bl -tag -width indent
168.It Dv MPOOL_DIRTY
169The page has been modified and needs to be written to the backing file.
170.El
171.Pp
172The
173.Fn mpool_put
174function
175returns 0 on success and -1 if an error occurs.
176.Pp
177The
178.Fn mpool_sync
179function writes all modified pages associated with the
180.Ft MPOOL
181pointer to the
182backing file.
183The
184.Fn mpool_sync
185function
186returns 0 on success and -1 if an error occurs.
187.Pp
188The
189.Fn mpool_close
190function free's up any allocated memory associated with the memory pool
191cookie.
192Modified pages are
193.Em not
194written to the backing file.
195The
196.Fn mpool_close
197function
198returns 0 on success and -1 if an error occurs.
199.Sh ERRORS
200The
201.Fn mpool_open
202function may fail and set
203.Va errno
204for any of the errors specified for the library routine
205.Xr malloc 3 .
206.Pp
207The
208.Fn mpool_get
209function may fail and set
210.Va errno
211for the following:
212.Bl -tag -width Er
213.It Bq Er EINVAL
214The requested record doesn't exist.
215.El
216.Pp
217The
218.Fn mpool_new
219and
220.Fn mpool_get
221functions may fail and set
222.Va errno
223for any of the errors specified for the library routines
224.Xr read 2 ,
225.Xr write 2 ,
226and
227.Xr malloc 3 .
228.Pp
229The
230.Fn mpool_sync
231function may fail and set
232.Va errno
233for any of the errors specified for the library routine
234.Xr write 2 .
235.Pp
236The
237.Fn mpool_close
238function may fail and set
239.Va errno
240for any of the errors specified for the library routine
241.Xr free 3 .
242.Sh SEE ALSO
243.Xr btree 3 ,
244.Xr dbopen 3 ,
245.Xr hash 3 ,
246.Xr recno 3
247