freemsg.9

7号信令功能代码,为开源代码

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.TH FREEMSG 9 "2004/01/12 23:33:00" "LiS-2_16_18-8" "Linux STREAMS DDI/DKI"
.SH NAME
.B freemsg
\- frees a \fISTREAMS\fR message
.SH SYNOPSIS
.PP
.B #include <sys/stream.h>
.HP 8
.BI "freemsg(struct msgb *" mp );
.SH DESCRIPTION
.PP
.BR freemsg ()
frees the
.IR STREAMS (4)
message pointed to by
.I mp
and the associated message blocks, data blocks and data buffers.
.PP
Freeing the message blocks of the message might or might not resultin the
deallocation of the message blocks, data blocks or data buffers, depending
upon the internal implementation, the binding of message blocks to data blocks
and whether the buffers are internal or external buffers.
.PP
For external data buffers that are to be freed, the
.I function
will be called with the
.I arg
provided previously to a
.BR esballoc (9)
call.
.SH "RETURN VALUES"
.PP
.BR freemsg ()
returns void.
.SH ERRORS
.PP
If the block pointer,
.IR bp ,
passed to
.BR freeb ()
is
.BR NULL ,
then
.BR freeb ()
will silently fail.
.SH CAVEATS
.PP
.BR freemsg (9)
is implemented with a looping call to
.BR freeb ().
.PP
.B LiS
.[
LiS
.]
uses a complicated message block and data block binding scheme with embedded
data buffers
.B FASTBUF
or less in size.  Determining the point at which a buffer is actually freed is
rather complicated.
.PP
In addition,
.B LiS
.[
LiS
.]
uses a free list to hold freed message blocks and data blocks.  It is
particularly inefficient for cache performance to do this.
.B LiS
.[
LiS
.]
should use kernel memory caches instead and should free the message blocks and
data blocks when they are no longer used to allow existing cache slots to be
reused.  Bypassing the kernel memory allocation and deallocation mechanisms
by using a free list results in poorer performance that might be suspected by
those that do not understand kernel memory chaching mechanisms.
.SH "SEE ALSO"
.PP
.BR allocb (9),
.BR esballoc "(9) and "
.BR freeb (9).
.SH VERSIONS
.PP
This manpage was written for
.B LiS\c
.
.[
LiS
.]
.PP
.BR freemsg ()
appeared first in SVR 3.
.[
svr3
.]
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