.\" $NetBSD: buffercache.9,v 1.2 2003/09/06 18:41:44 yamt Exp $ .\" .\" Copyright (c)2003 YAMAMOTO Takashi, .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" .\" following copyright notices are from sys/kern/vfs_bio.c. .\" they are here because i took some comments from it. yamt@netbsd.org .\" .\" .\"/*- .\" * Copyright (c) 1982, 1986, 1989, 1993 .\" * The Regents of the University of California. All rights reserved. .\" * (c) UNIX System Laboratories, Inc. .\" * All or some portions of this file are derived from material licensed .\" * to the University of California by American Telephone and Telegraph .\" * Co. or Unix System Laboratories, Inc. and are reproduced herein with .\" * the permission of UNIX System Laboratories, Inc. .\" * .\" * Redistribution and use in source and binary forms, with or without .\" * modification, are permitted provided that the following conditions .\" * are met: .\" * 1. Redistributions of source code must retain the above copyright .\" * notice, this list of conditions and the following disclaimer. .\" * 2. Redistributions in binary form must reproduce the above copyright .\" * notice, this list of conditions and the following disclaimer in the .\" * documentation and/or other materials provided with the distribution. .\" * 3. Neither the name of the University nor the names of its contributors .\" * may be used to endorse or promote products derived from this software .\" * without specific prior written permission. .\" * .\" * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" * SUCH DAMAGE. .\" * .\" * @(#)vfs_bio.c 8.6 (Berkeley) 1/11/94 .\" */ .\" .\"/*- .\" * Copyright (c) 1994 Christopher G. Demetriou .\" * .\" * Redistribution and use in source and binary forms, with or without .\" * modification, are permitted provided that the following conditions .\" * are met: .\" * 1. Redistributions of source code must retain the above copyright .\" * notice, this list of conditions and the following disclaimer. .\" * 2. Redistributions in binary form must reproduce the above copyright .\" * notice, this list of conditions and the following disclaimer in the .\" * documentation and/or other materials provided with the distribution. .\" * 3. All advertising materials mentioning features or use of this software .\" * must display the following acknowledgement: .\" * This product includes software developed by the University of .\" * California, Berkeley and its contributors. .\" * 4. Neither the name of the University nor the names of its contributors .\" * may be used to endorse or promote products derived from this software .\" * without specific prior written permission. .\" * .\" * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" * SUCH DAMAGE. .\" * .\" * @(#)vfs_bio.c 8.6 (Berkeley) 1/11/94 .\" */ .\" .\" .\" ------------------------------------------------------------ .Dd September 7, 2003 .Dt BUFFERCACHE 9 .Os .Sh NAME .Nm buffercache , .Nm bread , .Nm breada , .Nm breadn , .Nm bwrite , .Nm bawrite , .Nm bdwrite , .Nm getblk , .Nm geteblk , .Nm incore , .Nm allocbuf , .Nm brelse , .Nm biodone , .Nm biowait .Nd buffer cache interfaces .\" ------------------------------------------------------------ .Sh SYNOPSIS .In sys/buf.h .Ft void .Fn bread "struct vnode *vp" "daddr_t blkno" "int size" \ "struct ucred *cred" "struct buf **bpp" .Ft int .Fn breadn "struct vnode *vp" "daddr_t blkno" "int size" \ "daddr_t rablks[]" "int rasizes[]" "int nrablks" \ "struct ucred *cred" "struct buf **bpp" .Ft int .Fn breada "struct vnode *vp" "daddr_t blkno" "int size" \ "daddr_t rablkno" "int rabsize" \ "struct ucred *cred" "struct buf **bpp" .Ft int .Fn bwrite "struct buf *bp" .Ft void .Fn bawrite "struct buf *bp" .Ft void .Fn bdwrite "struct buf *bp" .Ft struct buf * .Fn getblk "struct vnode *vp" "daddr_t blkno" "int size" \ "int slpflag" "int slptimeo" .Ft struct buf * .Fn geteblk "int size" .Ft struct buf * .Fn incore "struct vnode *vp" "daddr_t blkno" .Ft void .Fn allocbuf "struct buf *bp" "int size" .Ft void .Fn brelse "struct buf *bp" .Ft void .Fn biodone "struct buf *bp" .Ft int .Fn biowait "struct buf *bp" .\" ------------------------------------------------------------ .Sh DESCRIPTION The .Nm interface is used by each filesystems to improve I/O performance using in-core caches of filesystem blocks. .\" XXX struct buf, B_ flags, MP locks, etc .\" ------------------------------------------------------------ .Sh FUNCTIONS .Bl -tag -width compact .It Fn bread "vp" "blkno" "size" "cred" "bpp" Read a block corresponding to .Fa vp and .Fa blkno . the buffer is returned via .Fa bpp . .Pp If the buffer is not found (i.e. the block is not cached in memory), .Fn bread allocates a buffer with enough pages for .Fa size and read the specified disk block into it using credential .Fa cred . .Pp The buffer returned by .Fn bread is marked as busy. (B_BUSY flag is set.) After manipulation of the buffer returned from .Fn bread , the caller should unbusy it so that another thread can get it. If the buffer contents are modified and should be written back to disk, it should be unbusied using one of variants of .Fn bwrite . Otherwise, it should be unbusied using .Fn brelse . .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn breadn "vp" "blkno" "size" "rablks" "rasizes" "nrablks" "cred" "bpp" Get a buffer as .Fn bread . In addition, .Fn breadn will start read-ahead of blocks specified by .Fn rablk , .Fn rasizes , .Fn nrablks . .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn breada "vp" "blkno" "size" "rablkno" "rabsize" "cred" "bpp" Same as .Fn breadn with single block read-ahead. This function is for compatibility with old filesystem code and shouldn't be used by new ones. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn bwrite "bp" Write a block. Start I/O for write using .Fn VOP_STRATEGY . Then, unless B_ASYNC flag is set in .Fa bp , .Fn bwrite waits for the I/O to complete. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn bawrite "bp" Write a block asynchronously. Set B_ASYNC flags in .Fa bp and simply call .Fa VOP_BWRITE , which results in .Fa bwrite for most filesystems. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn bdwrite "bp" Delayed write. Unlike .Fa bawrite , .Fa bdwrite won't start any I/O. It only mark the buffer as dirty (B_DELWRI) and unbusy it. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn getblk "vp" "blkno" "size" "slpflag" "slptimeo" Get a block of requested size .Fa size that is associated with a given vnode and block offset, specified by .Fa vp and .Fa blkno If it is found in the block cache, make it busy and return it. Otherwise, return an empty block of the correct size. It is up to the caller to insure that the cached blocks be of the correct size. .Pp If .Fn getblk needs to sleep, .Fa slpflag and .Fa slptimeo are used as arguments for .Fn ltsleep . .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn geteblk "size" Allocate an empty, disassociated block of a given size .Fa size . .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn incore "vp" "blkno" Determine if a block associated to a given vnode and block offset is in the cache. If it's there, return a pointer to it. Note that .Fn incore doesn't busy the buffer unlike .Fn getblk . .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn allocbuf "bp" "size" Expand or contract the actual memory allocated to a buffer. If the buffer shrinks, data is lost, so it's up to the caller to have written it out *first*; this routine will not start a write. If the buffer grows, it's the callers responsibility to fill out the buffer's additional contents. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn brelse "bp" Unbusy a buffer and release it to the free lists. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn biodone "bp" Mark I/O complete on a buffer. If a callback has been requested by B_CALL, do so. Otherwise, wakeup waiters. .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .It Fn biowait "bp" Wait for operations on the buffer to complete. When they do, extract and return the I/O's error value. .El .\" ------------------------------------------------------------ .Sh CODE REFERENCES This section describes places within the .Nx source tree where actual code implementing or using the name lookup subsystem can be found. All pathnames are relative to .Pa /usr/src . .Pp The buffer cache subsystem is implemented within the file .Pa sys/kern/vfs_bio.c . .Sh SEE ALSO .Xr intro 9 , .Xr vnode 9 .Rs .%A Marice J. Bach .%B "The Design of the UNIX Operating System" .%I "Prentice Hall" .%D 1986 .Re .Rs .%A Marshall Kirk McKusick .%A Keith Bostic .%A Michael J. Karels .%A John S. Quarterman .%B "The Design and Implementation of the 4.4BSD UNIX Operating System" .%I "Addison Welley" .%D 1996 .Re .\" ------------------------------------------------------------ .Sh BUGS In the current implementation, .Fn bread and its variants don't use a specified credential.