---
name: "md_done"
section: "9"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/md_done"
---

# md\_done(9)

set of functions to dissect an mbuf chain to various data types

## NAME

**mdchain**, **md\_initm**, **md\_done**, **md\_append\_record**, **md\_next\_record**, **md\_get\_uint8**, **md\_get\_uint16**, **md\_get\_uint16be**, **md\_get\_uint16le**, **md\_get\_uint32**, **md\_get\_uint32be**, **md\_get\_uint32le**, **md\_get\_int64**, **md\_get\_int64be**, **md\_get\_int64le**, **md\_get\_mem**, **md\_get\_mbuf**, **md\_get\_uio** – set of functions to dissect an mbuf chain to various data types

## SYNOPSIS

**options** **LIBMCHAIN** kldload libmchain

**#include \<sys/param.h\>**

**#include \<sys/uio.h\>**

**#include \<sys/mchain.h\>**

*void*\

**md\_initm**(*struct mdchain \*mdp*, *struct mbuf \*m*);

*void*\

**md\_done**(*struct mdchain \*mdp*);

*void*\

**md\_append\_record**(*struct mdchain \*mdp*, *struct mbuf \*top*);

*int*\

**md\_next\_record**(*struct mdchain \*mdp*);

*int*\

**md\_get\_uint8**(*struct mdchain \*mdp*, *u\_int8\_t \*x*);

*int*\

**md\_get\_uint16**(*struct mdchain \*mdp*, *u\_int16\_t \*x*);

*int*\

**md\_get\_uint16be**(*struct mdchain \*mdp*, *u\_int16\_t \*x*);

*int*\

**md\_get\_uint16le**(*struct mdchain \*mdp*, *u\_int16\_t \*x*);

*int*\

**md\_get\_uint32**(*struct mdchain \*mdp*, *u\_int32\_t \*x*);

*int*\

**md\_get\_uint32be**(*struct mdchain \*mdp*, *u\_int32\_t \*x*);

*int*\

**md\_get\_uint32le**(*struct mdchain \*mdp*, *u\_int32\_t \*x*);

*int*\

**md\_get\_int64**(*struct mdchain \*mdp*, *int64\_t \*x*);

*int*\

**md\_get\_int64be**(*struct mdchain \*mdp*, *int64\_t \*x*);

*int*\

**md\_get\_int64le**(*struct mdchain \*mdp*, *int64\_t \*x*);

*int*\

**md\_get\_mem**(*struct mdchain \*mdp*, *caddr\_t target*, *int size*, *int type*);

*int*\

**md\_get\_mbuf**(*struct mdchain \*mdp*, *int size*, *struct mbuf \*\*m*);

*int*\

**md\_get\_uio**(*struct mdchain \*mdp*, *struct uio \*uiop*, *int size*);

## DESCRIPTION

These functions are used to decompose mbuf chains to various data types. The *mdchain* structure is used as a working context and should be initialized through a call of the **mb\_initm**() function. It has the following fields:

- *md\_top*

  (*struct mbuf \**) A pointer to the top of the parsed mbuf chain.

- *md\_cur*

  (*struct mbuf \**) A pointer to the currently parsed mbuf.

- *md\_pas*

  (*int*) Offset in the current mbuf.

The **md\_done**() function disposes of an mbuf chain pointed to by the *mdp-\>md\_top* field and sets the field to NULL.

The **md\_append\_record**() appends a new mbuf chain using *m\_nextpkt* field to form a single linked list of mbuf chains. If the *mdp-\>md\_top* field is NULL, then this function behaves exactly as the **md\_initm**() function.

The **md\_next\_record**() function extracts the next mbuf chain and disposes the current one, if any. For a new mbuf chain it calls the **md\_initm**() function. If there is no data left the function returns ENOENT.

All **md\_get\_\***() functions perform an actual copy of the data from an mbuf chain. Functions which have **le** or **be** suffixes will perform conversion to the little- or big-endian data formats.

**md\_get\_mem**() function copies *size* bytes of data specified by the *source* argument from an mbuf chain. The *type* argument specifies the method used to perform a copy, and can be one of the following:

- MB\_MSYSTEM

  Use the **bcopy**() function.

- MB\_MUSER

  Use the [copyin(9)](/copyin/9.md) function.

- MB\_MINLINE

  Use an “inline” loop which does not call any function.

If *target* is NULL, an actual copy is not performed and the function just skips the given number of bytes.

## RETURN VALUES

All *int* functions return zero if successful, otherwise an error code is returned.

*Note*: after failure of any function, an mbuf chain is left in the broken state and only the **md\_done**() function can safely be called to destroy it.

## EXAMPLES

```
struct mdchain *mdp;
struct mbuf *m;
u_int16_t length;
u_int8_t byte;
receive(so, &m);
md_initm(mdp, m);
if (md_get_uint8(mdp, &byte) != 0 ||
    md_get_uint16le(mdp, &length) != 0)
	error = EBADRPC;
mb_done(mdp);
```

## SEE ALSO

[mbchain(9)](/mbchain/9.md), [mbuf(9)](/mbuf/9.md)

## AUTHORS

This manual page was written by Boris Popov ⟨bp@FreeBSD.org⟩.