M_TAG(9) | Kernel Developer's Manual | 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_delete_nonpersistent, m_tag_find, m_tag_copy, m_tag_copy_chain, m_tag_init, m_tag_first, m_tag_next — 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 *t);
void
m_tag_delete_nonpersistent(struct mbuf *);
struct m_tag *
m_tag_find(struct mbuf *m, int type, struct m_tag *t);
struct m_tag *
m_tag_copy(struct m_tag *m);
int
m_tag_copy_chain(struct mbuf *to, struct mbuf *from);
void
m_tag_init(struct mbuf *m);
struct m_tag *
m_tag_first(struct mbuf *m);
struct m_tag *
m_tag_next(struct mbuf *m, struct m_tag *t);

# 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, t)
  Unlink and free mbuf tags beginning with the mbuf tag t from the mbuf m. If t is `NULL`, m_tag_delete_chain() unlinks and frees all mbuf tags associated with the mbuf m.
m_tag_delete_nonpersistent(m)
  Unlink and free all non persistent tags associated with the mbuf m.
m_tag_find(m, type, t)
  Find an mbuf tag with type type after the mbuf tag t in the tag chain associated with the mbuf m. If t is `NULL`, search from the first mbuf tag. 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.
m_tag_init(m)
  Initialize mbuf tag chain of the mbuf m.
m_tag_first(m)
  Return the first mbuf tag associated with the mbuf m. Return `NULL` if no mbuf tags are found.
m_tag_next(m, t)
  Return the next mbuf tag after t associated with the mbuf m. Return `NULL` if t is the last tag in the chain.

# CODE REFERENCES

The mbuf tagging interfaces are implemented within the file sys/kern/uipc_mbuf2.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.

September 7, 2004 | NetBSD 8.2