dupmsg.9

7号信令功能代码,为开源代码

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.TH DUPMSG 9 "2004/01/12 23:32:59" "LiS-2_16_18-8" "Linux STREAMS DDI/DKI"
.SH NAME
.B dupmsg
\- duplicate a \fISTREAMS\fR message
.SH SYNOPSIS
.PP
.B #include <sys/stream.h>
.HP 8
.BI "mblk_t *" msg " = dupmsg(mblk_t *" mp );
.SH DESCRIPTION
.PP
.BR dupmsg ()
duplicates all of the message blocks of a message, keeping the same data
blocks.
The data blocks are reused.  Each data block will have its reference counter
incremented.  If one duplicate message alters the data in a data block, the
change affects all duplicate messages.
.SH "RETURN VALUES"
.PP
Upon success,
.BR dupmsg ()
returns a pointer to the duplicate message,
.IR msg .
.PP
Upon failure,
.BR dupmsg ()
returns
.BR NULL .
.SH ERRORS
.PP
When
.BR dupmsg ()
fails it returns
.BR NULL .
.BR dupmsg ()
fails when the passed in message pointer
.I mp
is
.BR NULL ;
or an allocation failure occurs ona message block while duplicating.
.PP
Normally, if
.BR dupmsg ()
fails and
.I mp
is not
.BR NULL ,
.BR esbbcall(9) 
should be called with the
.I priority
associated with the message for which duplication failed.
.SH CAVEATS
.PP
.B LiS
.[
LiS
.]
implements
.BR dupmsg ()
as a looping call to
.BR dupb (9).
One call is to
.BR dupb (9)
is made for each message block.  If
.BR dupb (9)
fails, the partially duplicated message is freed using
.BR freemsg (9).
.SH BUGS
.PP
.B LiS
.[
LiS
.]
used to have some problems serializing access to the reference count in data
blocks which caused inconsistencies in the reference count when duplicate
messages were freed.
.SH "SEE ALSO"
.PP
.BR dupb (9),
.BR copyb (9),
.BR copymsg (9),
.BR freemsg (9).
.SH HISTORY
.PP
.BR dupmsg ()
first appeared in SVR 3.
.[
svr3
.]
.SH VERSIONS
.PP
This manpage was written for
.B LiS\c
.
.[
LiS
.]
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