M_TAG(9)

NAME
m_tag, m_tag_get, m_tag_free, m_tag_prepend, m_tag_unlink, m_tag_delete, m_tag_delete_chain, m_tag_find, m_tag_copy, m_tag_copy_chain - mbuf tagging interfaces

SYNOPSIS
#include <sys/mbuf.h>
struct m_tag *
m_tag_get(int type, int len, int wait);
void
m_tag_free(struct m_tag *t);
void
m_tag_prepend(struct mbuf *m, struct m_tag *t);
void
m_tag_unlink(struct mbuf *m, struct m_tag *t);
void
m_tag_delete(struct mbuf *m, struct m_tag *t);
void
m_tag_delete_chain(struct mbuf *m);
struct m_tag *
m_tag_find(struct mbuf *m, int type);
struct m_tag *
m_tag_copy(struct m_tag *m);
int
m_tag_copy_chain(struct mbuf *to, struct mbuf *from);

DESCRIPTION
The m_tag interface is used to “tag” mbufs.

FUNCTIONS

m_tag_get(type, len, wait)
    Allocate an mbuf tag. type is one of the PACKET_TAG_ macros. len is the size of the data associated with the tag, in bytes. wait is either M_WAITOK or M_NOWAIT.

m_tag_free(t)
    Free the mbuf tag t.

m_tag_prepend(m, t)
    Prepend the mbuf tag t to the mbuf m. t will become the first tag of the mbuf m. When m is freed, t will also be freed.

m_tag_unlink(m, t)
    Unlink the mbuf tag t from the mbuf m.

m_tag_delete(m, t)
    The same as m_tag_unlink() followed by m_tag_free().

m_tag_delete_chain(m)
    Unlink and free mbuf tags from the mbuf m.

m_tag_find(m, type)
    Find an mbuf tag with type type in the tag chain associated with the mbuf m. If an mbuf tag is found, return a pointer to it. Otherwise return NULL.

m_tag_copy(t)
    Copy an mbuf tag t. Return a new mbuf tag on success. Otherwise return NULL.

m_tag_copy_chain(to, from)
    Copy all mbuf tags associated with the mbuf from to the mbuf to. If to already has any mbuf tags, they will be unlinked and freed beforehand. Return 1 on success. Otherwise return 0.

CODE REFERENCES
The mbuf tagging interfaces are implemented within the file sys/kern/uipc_mbuf.c.

The PACKET_TAG_ macros are defined in the file sys/sys/mbuf.h.

SEE ALSO
intro(9), malloc(9), mbuf(9)

BUGS
The semantics of the term "persistent tag" are vague.