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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd June 17, 2011 29.Dt MPOOL 3 30.Os 31.Sh NAME 32.Nm mpool 33.Nd "shared memory buffer pool" 34.Sh SYNOPSIS 35.In db.h 36.In mpool.h 37.Ft MPOOL * 38.Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache" 39.Ft void 40.Fo mpool_filter 41.Fa "MPOOL *mp" 42.Fa "void (*pgin)(void *, pgno_t, void *)" 43.Fa "void (*pgout)(void *, pgno_t, void *)" 44.Fa "void *pgcookie" 45.Fc 46.Ft void * 47.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr" "u_int flags" 48.Ft int 49.Fn mpool_delete "MPOOL *mp" "void *page" 50.Ft void * 51.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags" 52.Ft int 53.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags" 54.Ft int 55.Fn mpool_sync "MPOOL *mp" 56.Ft int 57.Fn mpool_close "MPOOL *mp" 58.Sh DESCRIPTION 59The 60.Nm mpool 61library interface is intended to provide page oriented buffer management 62of files. 63.Pp 64The 65.Fn mpool_open 66function initializes a memory pool. 67The 68.Fa key 69argument is currently ignored. 70The 71.Fa fd 72argument is a file descriptor for the underlying file, which must be seekable. 73.Pp 74The 75.Fa pagesize 76argument is the size, in bytes, of the pages into which the file is broken up. 77The 78.Fa maxcache 79argument is the maximum number of pages from the underlying file to cache 80at any one time. 81This value is not relative to the number of processes which share a file's 82buffers, but will be the largest value specified by any of the processes 83sharing the file. 84.Pp 85The 86.Fn mpool_filter 87function is intended to make transparent input and output processing of the 88pages possible. 89If the 90.Fa pgin 91function is specified, it is called each time a buffer is read into the memory 92pool from the backing file. 93If the 94.Fa pgout 95function is specified, it is called each time a buffer is written into the 96backing file. 97Both functions are called with the 98.Fa pgcookie 99pointer, the page number and a pointer to the page to being read or written. 100.Pp 101The function 102.Fn mpool_new 103takes an 104.Dv MPOOL 105pointer, an address, and a set of flags as arguments. 106If a new page can be allocated, a pointer to the page is returned and 107the page number is stored into the 108.Fa pgnoaddr 109address. 110Otherwise, 111.Dv NULL 112is returned and 113.Va errno 114is set. 115The flags value is formed by 116.Tn OR Ns 'ing 117the following values: 118.Bl -tag -width Ds 119.It Dv MPOOL_PAGE_REQUEST 120Allocate a new page with a specific page number. 121.It Dv MPOOL_PAGE_NEXT 122Allocate a new page with the next page number. 123.El 124.Pp 125The function 126.Fn mpool_delete 127deletes the specified page from a pool and frees the page. 128It takes an 129.Dv MPOOL 130pointer and a page as arguments. 131The page must have been generated by 132.Fn mpool_new . 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 specified by 148.Em or Ns 'ing 149any of the following values: 150.Bl -tag -width indent 151.It Dv MPOOL_IGNOREPIN 152The page returned is not pinned; 153page will otherwise be pinned on return. 154.El 155.Pp 156The 157.Fn mpool_put 158function unpins the page referenced by 159.Fa pgaddr . 160The 161.Fa pgaddr 162argument 163must be an address previously returned by 164.Fn mpool_get 165or 166.Fn mpool_new . 167The 168.Fa flags 169argument is specified by 170.Em or Ns 'ing 171any of the following values: 172.Bl -tag -width indent 173.It Dv MPOOL_DIRTY 174The page has been modified and needs to be written to the backing file. 175.El 176.Pp 177The 178.Fn mpool_put 179function 180returns 0 on success and -1 if an error occurs. 181.Pp 182The 183.Fn mpool_sync 184function writes all modified pages associated with the 185.Ft MPOOL 186pointer to the 187backing file. 188The 189.Fn mpool_sync 190function 191returns 0 on success and -1 if an error occurs. 192.Pp 193The 194.Fn mpool_close 195function free's up any allocated memory associated with the memory pool 196cookie. 197Modified pages are 198.Em not 199written to the backing file. 200The 201.Fn mpool_close 202function 203returns 0 on success and -1 if an error occurs. 204.Sh ERRORS 205The 206.Fn mpool_open 207function may fail and set 208.Va errno 209for any of the errors specified for the library routine 210.Xr malloc 3 . 211.Pp 212The 213.Fn mpool_get 214function may fail and set 215.Va errno 216for the following: 217.Bl -tag -width Er 218.It Bq Er EINVAL 219The requested record does not exist. 220.El 221.Pp 222The 223.Fn mpool_new 224and 225.Fn mpool_get 226functions may fail and set 227.Va errno 228for any of the errors specified for the library routines 229.Xr read 2 , 230.Xr write 2 , 231and 232.Xr malloc 3 . 233.Pp 234The 235.Fn mpool_sync 236function may fail and set 237.Va errno 238for any of the errors specified for the library routine 239.Xr write 2 . 240.Pp 241The 242.Fn mpool_close 243function may fail and set 244.Va errno 245for any of the errors specified for the library routine 246.Xr free 3 . 247.Sh SEE ALSO 248.Xr btree 3 , 249.Xr dbopen 3 , 250.Xr hash 3 , 251.Xr recno 3 252