.\"     $NetBSD: m_tag.9,v 1.8 2018/11/15 10:23:55 maxv Exp $
.\"
.\" Copyright (c)2004 YAMAMOTO Takashi,
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" ------------------------------------------------------------
.Dd November 15, 2018
.Dt M_TAG 9
.Os
.Sh NAME
.Nm m_tag ,
.Nm m_tag_get ,
.Nm m_tag_free ,
.Nm m_tag_prepend ,
.Nm m_tag_unlink ,
.Nm m_tag_delete ,
.Nm m_tag_delete_chain ,
.Nm m_tag_find ,
.Nm m_tag_copy ,
.Nm m_tag_copy_chain
.Nd mbuf tagging interfaces
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/mbuf.h
.Ft struct m_tag *
.Fn m_tag_get "int type" "int len" "int wait"
.Ft void
.Fn m_tag_free "struct m_tag *t"
.Ft void
.Fn m_tag_prepend "struct mbuf *m" "struct m_tag *t"
.Ft void
.Fn m_tag_unlink "struct mbuf *m" "struct m_tag *t"
.Ft void
.Fn m_tag_delete "struct mbuf *m" "struct m_tag *t"
.Ft void
.Fn m_tag_delete_chain "struct mbuf *m"
.Ft struct m_tag *
.Fn m_tag_find "struct mbuf *m" "int type"
.Ft struct m_tag *
.Fn m_tag_copy "struct m_tag *m"
.Ft int
.Fn m_tag_copy_chain "struct mbuf *to" "struct mbuf *from"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
The
.Nm
interface is used to
.Dq tag
mbufs.
.\" XXX PACKET_TAG_*
.\" ------------------------------------------------------------
.Sh FUNCTIONS
.Bl -tag -width compact
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_get "type" "len" "wait"
Allocate an mbuf tag.
.Fa type
is one of the
.Dv PACKET_TAG_
macros.
.Fa len
is the size of the data associated with the tag, in bytes.
.Fa wait
is either
.Dv M_WAITOK
or
.Dv M_NOWAIT .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_free "t"
Free the mbuf tag
.Fa t .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_prepend "m" "t"
Prepend the mbuf tag
.Fa t
to the mbuf
.Fa m .
.Fa t
will become the first tag of the mbuf
.Fa m .
When
.Fa m
is freed,
.Fa t
will also be freed.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_unlink "m" "t"
Unlink the mbuf tag
.Fa t
from the mbuf
.Fa m .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_delete "m" "t"
The same as
.Fn m_tag_unlink
followed by
.Fn m_tag_free .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_delete_chain "m"
Unlink and free mbuf tags from the mbuf
.Fa m .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_find "m" "type"
Find an mbuf tag with type
.Fa type
in the tag chain associated with the mbuf
.Fa m .
If an mbuf tag is found, return a pointer to it.
Otherwise return
.Dv NULL .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_copy "t"
Copy an mbuf tag
.Fa t .
Return a new mbuf tag on success.
Otherwise return
.Dv NULL .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn m_tag_copy_chain "to" "from"
Copy all mbuf tags associated with the mbuf
.Fa from
to the mbuf
.Fa to .
If
.Fa to
already has any mbuf tags, they will be unlinked and freed beforehand.
Return 1 on success.
Otherwise return 0.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.El
.\" ------------------------------------------------------------
.Sh CODE REFERENCES
The mbuf tagging interfaces are implemented within the file
.Pa sys/kern/uipc_mbuf.c .
.Pp
The
.Dv PACKET_TAG_
macros are defined in the file
.Pa sys/sys/mbuf.h .
.Sh SEE ALSO
.Xr intro 9 ,
.Xr malloc 9 ,
.Xr mbuf 9
.\" ------------------------------------------------------------
.Sh BUGS
The semantics of the term "persistent tag" are vague.