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diff --git a/share/man/man9/pbuf.9 b/share/man/man9/pbuf.9 new file mode 100644 index 000000000000..4329ac9c84fe --- /dev/null +++ b/share/man/man9/pbuf.9 @@ -0,0 +1,132 @@ +.\" +.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. 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(s), this list of conditions and the following disclaimer as +.\" the first lines of this file unmodified other than the possible +.\" addition of one or more copyright notices. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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. +.\" +.\" $FreeBSD$ +.\" +.Dd July 9, 2001 +.Dt PBUF 9 +.Os +.Sh NAME +.Nm pbuf , +.Nm getpbuf , +.Nm trypbuf , +.Nm relpbuf +.Nd "functions for managing physical buffers" +.Sh SYNOPSIS +.In sys/param.h +.In sys/systm.h +.In sys/bio.h +.In sys/buf.h +.Ft "struct buf *" +.Fn getpbuf "int *pfreecnt" +.Ft "struct buf *" +.Fn trypbuf "int *pfreecnt" +.Ft void +.Fn relpbuf "struct buf *bp" "int *pfreecnt" +.Sh DESCRIPTION +These functions are used to allocate and release physical buffers. +.Pp +The physical buffers are allocated at system startup and are +maintained in a separate pool from the main system buffers. +They are intended for use by subsystems that cannot or should not be +reliant on the main pool of buffers (for example the swap pager). +The system allocates between 16 and 256 physical buffers depending +on the amount of memory in the system. +.Pp +Each subsystem that allocates buffers via these calls is expected +to manage its own percentage free counter. +If the value is initialized to \-1 the number of buffers available +to the subsystem is limited only by the number of physical buffers +available. +The number of buffers is stored in +.Va nswbuf +which is defined in +.In sys/buf.h +and initialized in +.Fn cpu_startup . +A recommended initialization value is 1/2 +.Va nswbuf . +.Pp +The +.Fn getpbuf +function returns the first available buffer to the user. +If there are no buffers available, +.Fn getpbuf +will sleep waiting for one to become available. +If +.Fa pfreecnt +is zero, +.Fn getpbuf +will sleep until it increases. +.Fa pfreecnt +is decremented prior to returning. +.Pp +The +.Fn trypbuf +function returns the first available buffer. +If there are no buffers available, +.Dv NULL +is returned. +As well, if +.Fa pfreecnt +is zero, +.Dv NULL +is returned. +.Fa pfreecnt +is decremented prior to returning a valid buffer. +If +.Dv NULL +is returned, +.Fa pfreecnt +is not modified. +.Pp +The +.Fn relpbuf +function releases the buffer back to the free list. +If the buffers +.Va b_rcred +or +.Va b_wcred +structures are not +.Dv NULL , +they are freed. +See +.Xr crfree 9 . +.Pp +.Fa pfreecnt +is incremented prior to returning. +.Sh RETURN VALUES +.Fn getpbuf +and +.Fn trypbuf +return a pointer to the buffer. +In the case of +.Fn trypbuf , +.Dv NULL +can also be returned indicating that there are no buffers available. +.Sh AUTHORS +This manual page was written by +.An Chad David Aq davidc@acns.ab.ca . |