relpbuf man page on FreeBSD

Man page or keyword search:  
man Server   9747 pages
apropos Keyword Search (all sections)
Output format
FreeBSD logo
[printable version]

PBUF(9)			 BSD Kernel Developer's Manual		       PBUF(9)

     pbuf, getpbuf, trypbuf, relpbuf — functions for managing physical buffers

     #include <sys/param.h>
     #include <sys/systm.h>
     #include <sys/bio.h>
     #include <sys/buf.h>

     struct buf *
     getpbuf(int *pfreecnt);

     struct buf *
     trypbuf(int *pfreecnt);

     relpbuf(struct buf *bp, int *pfreecnt);

     These functions are used to allocate and release physical buffers.

     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.

     Each subsystem that allocates buffers via these calls is expected to man‐
     age 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
     nswbuf which is defined in <sys/buf.h> and initialized in cpu_startup().
     A recommended initialization value is 1/2 nswbuf.

     The getpbuf() function returns the first available buffer to the user.
     If there are no buffers available, getpbuf() will sleep waiting for one
     to become available.  If pfreecnt is zero, getpbuf() will sleep until it
     increases.	 pfreecnt is decremented prior to returning.

     The trypbuf() function returns the first available buffer.	 If there are
     no buffers available, NULL is returned.  As well, if pfreecnt is zero,
     NULL is returned.	pfreecnt is decremented prior to returning a valid
     buffer.  If NULL is returned, pfreecnt is not modified.

     The relpbuf() function releases the buffer back to the free list.	If the
     buffers b_rcred or b_wcred structures are not NULL, they are freed.  See

     pfreecnt is incremented prior to returning.

     getpbuf() and trypbuf() return a pointer to the buffer.  In the case of
     trypbuf(), NULL can also be returned indicating that there are no buffers

     This manual page was written by Chad David ⟨⟩.

BSD				 July 9, 2001				   BSD

List of man pages available for FreeBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net