man3/mpool.3

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  32 .\"     @(#)mpool.3     8.1 (Berkeley) 6/4/93
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  34 .TH MPOOL 3 1993-06-04 "" "Linux Programmer's Manual"
  35 .UC 7
  36 .SH NAME
  37 mpool \- shared memory buffer pool
  38 .SH SYNOPSIS
  39 .nf
  40 .ft B
  41 #include <db.h>
  42 #include <mpool.h>
  43
  44 MPOOL *
  45 mpool_open (DBT *key, int fd, pgno_t pagesize, pgno_t maxcache);
  46
  47 void
  48 mpool_filter (MPOOL *mp, void (*pgin)(void *, pgno_t, void *),
  49 .ti +5
  50 void (*pgout)(void *, pgno_t, void *), void *pgcookie);
  51
  52 void *
  53 mpool_new (MPOOL *mp, pgno_t *pgnoaddr);
  54
  55 void *
  56 mpool_get (MPOOL *mp, pgno_t pgno, u_int flags);
  57
  58 int
  59 mpool_put (MPOOL *mp, void *pgaddr, u_int flags);
  60
  61 int
  62 mpool_sync (MPOOL *mp);
  63
  64 int
  65 mpool_close (MPOOL *mp);
  66 .ft R
  67 .fi
  68 .SH DESCRIPTION
  69 .I Mpool
  70 is the library interface intended to provide page oriented buffer management
  71 of files.
  72 The buffers may be shared between processes.
  73 .PP
  74 The function
  75 .BR mpool_open ()
  76 initializes a memory pool.
  77 The
  78 .I key
  79 argument is the byte string used to negotiate between multiple
  80 processes wishing to share buffers.
  81 If the file buffers are mapped in shared memory, all processes using
  82 the same key will share the buffers.
  83 If
  84 .I key
  85 is NULL, the buffers are mapped into private memory.
  86 The
  87 .I fd
  88 argument is a file descriptor for the underlying file, which must be seekable.
  89 If
  90 .I key
  91 is non-NULL and matches a file already being mapped, the
  92 .I fd
  93 argument is ignored.
  94 .PP
  95 The
  96 .I pagesize
  97 argument is the size, in bytes, of the pages into which the file is broken up.
  98 The
  99 .I maxcache
 100 argument is the maximum number of pages from the underlying file to cache
 101 at any one time.
 102 This value is not relative to the number of processes which share a file's
 103 buffers, but will be the largest value specified by any of the processes
 104 sharing the file.
 105 .PP
 106 The
 107 .BR mpool_filter ()
 108 function is intended to make transparent input and output processing of the
 109 pages possible.
 110 If the
 111 .I pgin
 112 function is specified, it is called each time a buffer is read into the memory
 113 pool from the backing file.
 114 If the
 115 .I pgout
 116 function is specified, it is called each time a buffer is written into the
 117 backing file.
 118 Both functions are called with the
 119 .I pgcookie
 120 pointer, the page number and a pointer to the page to being read or written.
 121 .PP
 122 The function
 123 .BR mpool_new ()
 124 takes an
 125 .I MPOOL
 126 pointer and an address as arguments.
 127 If a new page can be allocated, a pointer to the page is returned and
 128 the page number is stored into the
 129 .I pgnoaddr
 130 address.
 131 Otherwise, NULL is returned and
 132 .I errno
 133 is set.
 134 .PP
 135 The function
 136 .BR mpool_get ()
 137 takes an
 138 .I MPOOL
 139 pointer and a page number as arguments.
 140 If the page exists, a pointer to the page is returned.
 141 Otherwise, NULL is returned and
 142 .I errno
 143 is set.
 144 The flags parameter is not currently used.
 145 .PP
 146 The function
 147 .BR mpool_put ()
 148 unpins the page referenced by
 149 .IR pgaddr .
 150 .I pgaddr
 151 must be an address previously returned by
 152 .BR mpool_get ()
 153 or
 154 .BR mpool_new ().
 155 The flag value is specified by
 156 .IR or 'ing
 157 any of the following values:
 158 .TP
 159 .B MPOOL_DIRTY
 160 The page has been modified and needs to be written to the backing file.
 161 .PP
 162 .BR mpool_put ()
 163 returns 0 on success and \-1 if an error occurs.
 164 .PP
 165 The function
 166 .BR mpool_sync ()
 167 writes all modified pages associated with the
 168 .I MPOOL
 169 pointer to the
 170 backing file.
 171 .BR mpool_sync ()
 172 returns 0 on success and \-1 if an error occurs.
 173 .PP
 174 The
 175 .BR mpool_close ()
 176 function free's up any allocated memory associated with the memory pool
 177 cookie.
 178 Modified pages are
 179 .B not
 180 written to the backing file.
 181 .BR mpool_close ()
 182 returns 0 on success and \-1 if an error occurs.
 183 .SH ERRORS
 184 The
 185 .BR mpool_open ()
 186 function may fail and set
 187 .I errno
 188 for any of the errors specified for the library routine
 189 .BR malloc (3).
 190 .PP
 191 The
 192 .BR mpool_get ()
 193 function may fail and set
 194 .I errno
 195 for the following:
 196 .TP 15
 197 .B EINVAL
 198 The requested record doesn't exist.
 199 .PP
 200 The
 201 .BR mpool_new ()
 202 and
 203 .BR mpool_get ()
 204 functions may fail and set
 205 .I errno
 206 for any of the errors specified for the library routines
 207 .BR read (2),
 208 .BR write (2),
 209 and
 210 .BR malloc (3).
 211 .PP
 212 The
 213 .BR mpool_sync ()
 214 function may fail and set
 215 .I errno
 216 for any of the errors specified for the library routine
 217 .BR write (2).
 218 .PP
 219 The
 220 .BR mpool_close ()
 221 function may fail and set
 222 .I errno
 223 for any of the errors specified for the library routine
 224 .BR free (3).
 225 .SH "CONFORMING TO"
 226 Not in POSIX.1-2001.
 227 Present on the BSDs.
 228 .SH "SEE ALSO"
 229 .BR dbopen (3),
 230 .BR btree (3),
 231 .BR hash (3),
 232 .BR recno (3)