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.\"  Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
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.Dd $Mdocdate: January 23 2020 $
.Dt ML_INIT 9
.Os
.Sh NAME
.Nm ml_init ,
.Nm ml_enqueue ,
.Nm ml_dequeue ,
.Nm ml_enlist ,
.Nm ml_dechain ,
.Nm ml_len ,
.Nm ml_empty ,
.Nm ml_hdatalen ,
.Nm ml_purge ,
.Nm MBUF_LIST_INITIALIZER ,
.Nm MBUF_LIST_FIRST ,
.Nm MBUF_LIST_NEXT ,
.Nm MBUF_LIST_FOREACH
.Nd mbuf list API
.Sh SYNOPSIS
.In sys/mbuf.h
.Ft void
.Fn ml_init "struct mbuf_list *ml"
.Ft void
.Fn ml_enqueue "struct mbuf_list *ml" "struct mbuf *m"
.Ft struct mbuf *
.Fn ml_dequeue "struct mbuf_list *ml"
.Ft void
.Fn ml_enlist "struct mbuf_list *ml" "struct mbuf_list *src"
.Ft struct mbuf *
.Fn ml_dechain "struct mbuf_list *ml"
.Ft unsigned int
.Fn ml_len "struct mbuf_list *ml"
.Ft int
.Fn ml_empty "struct mbuf_list *ml"
.Ft unsigned int
.Fn ml_hdatalen "struct mbuf_list *ml"
.Ft unsigned int
.Fn ml_purge "struct mbuf_list *ml"
.Ft struct mbuf_list
.Fn MBUF_LIST_INITIALIZER
.Ft struct mbuf *
.Fn MBUF_LIST_FIRST "struct mbuf_list *ml"
.Ft struct mbuf *
.Fn MBUF_LIST_NEXT "struct mbuf *m"
.Fn MBUF_LIST_FOREACH "struct mbuf_list *ml" "VARNAME"
.Sh DESCRIPTION
The mbuf list API provides implementations of data structures and operations
for managing lists of mbufs between contexts.
.Pp
mbuf_list structures support the following functionality:
.Pp
.Bl -enum -compact -offset indent
.It
Insertion of a new mbuf at the end of the list.
.It
Removal of an mbuf from the head of the list.
.El
.Bl -tag -width Ds
.It Fn ml_init "struct mbuf_list *ml"
Initialise the
.Fa ml
mbuf_list structure.
.It Fn MBUF_LIST_INITIALIZER
An initialiser for an mbuf_list structure declaration.
.It Fn ml_enqueue "struct mbuf_list *ml" "struct mbuf *m"
Enqueue mbuf
.Fa m
on the end of the
.Fa ml
mbuf list.
.It Fn ml_dequeue "struct mbuf_list *ml"
Dequeue an mbuf from the front of the
.Fa ml
mbuf list.
.It Fn ml_enlist "struct mbuf_list *ml" "struct mbuf_list *src"
Enqueue all the mbufs on the
.Fa src
mbuf list on to the end of the
.Fa ml
mbuf list.
.It Fn ml_dechain "struct mbuf_list *ml"
Dequeues all mbufs from the
.Fa ml
mbuf list.
.It Fn ml_len "struct mbuf_list *ml"
Return the number of mbufs on the
.Fa ml
mbuf list.
.It Fn ml_empty "struct mbuf_list *ml"
Return if the
.Fa ml
mbuf list is empty.
.It Fn ml_hdatalen "struct mbuf_list *ml"
Return the number of bytes in the packet at the head of the
.Fa ml
mbuf list.
.It Fn ml_purge "struct mbuf_list *ml"
Free all the mbufs on the
.Fa ml
mbuf list.
.It Fn MBUF_LIST_FIRST "struct mbuf_list *ml"
Access the first mbuf in the
.Fa ml
mbuf list for traversal.
.It Fn MBUF_LIST_NEXT "struct mbuf *m"
Access the next mbuf in the mbuf list after
.Fa m .
.It Fn MBUF_LIST_FOREACH "struct mbuf_list *ml" "VARNAME"
A convenience macro that can be used to iterate over the contents of the
.Fa ml
mbuf list.
.Fa VARNAME
identifies the name (not the address) of an mbuf pointer that will
be set to each entry on the list.
Note that it is unsafe to modify the list while iterating over it.
.El
.Sh CONTEXT
.Fn ml_init ,
.Fn ml_enqueue ,
.Fn ml_dequeue ,
.Fn ml_enlist ,
.Fn ml_dechain ,
.Fn ml_len ,
.Fn ml_empty ,
.Fn ml_purge ,
.Fn MBUF_LIST_INITIALIZER ,
.Fn MBUF_LIST_FIRST ,
.Fn MBUF_LIST_NEXT ,
and
.Fn MBUF_LIST_FOREACH
can be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Fn ml_dequeue
returns the mbuf that was at the head of its list.
If the list was empty,
.Dv NULL
is returned.
.Pp
.Fn ml_dechain
returns all the mbufs that were on the list via
a pointer to an mbuf with the chain accessible via m_nextpkt members.
If the list was empty,
.Dv NULL
is returned.
.Pp
.Fn ml_len
returns the number of mbufs on the list.
.Pp
.Fn ml_empty
return a non-zero value if the list is empty, otherwise 0.
.Pp
.Fn ml_hdatalen
returns the size of a packet on the list, or 0 if the list is empty.
.Pp
.Fn ml_purge
returns the number of mbufs that were freed.
.Pp
.Fn MBUF_LIST_FIRST
returns the first mbuf in the mbuf list, or
.Dv NULL
if the list is empty.
.Pp
.Fn MBUF_LIST_NEXT
returns the next mbuf in the mbuf list, or
.Dv NULL
if the end of the list has been reached.
.Sh SEE ALSO
.Xr mbuf 9