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IXP400 Software
Buffer Management
Programmer’s Guide IXP400 Software Version 2.0 April 2005
Document Number: 252539, Revision: 007 47
Note that the M_BLK structure contains many fields that are not used by the IXP400 software.
These fields are simply ignored and are not modified by the IXP400 software.
M_BLK buffers support two levels of buffer chaining:
• buffer chaining — Each buffer can be chained together to form a packet. This is achieved
using the IX_MBUF_NEXT_BUFFER_IN_PKT_PTR equivalent field in the M_BLK. This
is supported and required by the IXP400 software.
• packet chaining — Each packet can consist of a chain of one or more buffers. Packets can also
be chained together (to form a chain of chains). This is not used by the IXP400 software. The
IX_MBUF_NEXT_PKT_IN_CHAIN_PTR equivalent field of the M_BLK buffer structure is
used for this purpose. Most IXP400 software components will ignore this field.
Note: The VxWorks netMbuf pool library functions will not be supported to allocate and free the
IXP_BUF buffers.
Table 3 shows the field mapping between the IX_MBUF and the M_BLK buffer structures through
OSAL macros.
3.6.2 Linux* skbuff Buffer
The buffer format native to the Linux OS is the “skbuff” buffer structure, which is significantly
different from the IX_MBUF buffer format used by the IXP400 software.
The Linux skbuf structure is attached to the os_buf_ptr field during transmit or receive and is
detached during TxDone. The user must allocate an IXP_BUF header, make a call to a translational
function and pass the IXP_BUF buffer to the IXP400 software release. The translation functions
enter all the required fields from the OS buffers to respective fields in the first structure, that is, the
IX_MBUF structure within the IXP_BUF structure. The translation of fields from the IX_MBUF
structure into the NPE shared structure is accomplished by the OSAL component on Transmit and
Receive Replenish. On TxDone the user may recycle the IXP_BUF back to the IXP_BUF_POOL
or to an internal data structure.
The OSAL layer provides buffer translation macros for users to translate OS-specific buffer
formats to IXP_BUF buffer format and vice versa.
Table 3. IX_MBUF to M_BLK Mapping
IX_MBUF M_BLK
IX_OSAL_MBUF_NEXT_BUFFER_IN_PKT_PTR mBlkHdr.mNext
IX_OSAL_MBUF_NEXT_PKT_IN_CHAIN_PTR mBlkHdr.mNextPkt
IX_OSAL_MBUF_MDATA mBlkHdr.mData
IX_OSAL_MBUF_MLEN mBlkHdr.mLen
IX_OSAL_MBUF_TYPE mBlkHdr.mType
IX_OSAL_MBUF_FLAGS mBlkHdr.mFlags
IX_OSAL_reserved mBlkHdr.reserved
IX_OSAL_MBUF_NET_POOL mBlkPktHdr.rcvif
IX_OSAL_MBUF_PKT_LEN mBlkPktHdr.len
priv pClBlk