Intel IXP400 Buffer Translation Functions, Following fields will get updated in the skbuffer

Intel® IXP400 Software

Buffer Management

It works on the following principles:

•Each IXP_BUF is mapped to an skbuff (1:1 mapping)

•The os_buf_ptr field of the ix_ctrl structure is used to store a pointer to the corresponding skbuff.

•The ix_data pointer field of the IX_MBUF structure within the IXP_BUF structure will be set to point to the data field of the corresponding skbuff through use of the IX_OSAL_MBUF_MDATA macro.

•The ix_len and ix_pkt_len fields of the IX_MBUF structure within the IXP_BUF structure will be set to the length of the skbuff data section (the len field in the skbuff structure) through use of the IX_OSAL_MBUF_PKT_LEN and IX_OSAL_MBUF_MLEN macros.

The prototype for this function is shown in Table 4.

Table 4. Buffer Translation Functions

•IX_OSAL_CONVERT_OSBUF_TO_IXPBUF(osBufPtr,ixpBufPtr)

The following fields of IX_MBUF within the IXP_BUF structure will get updated:

—ix_len

—ix_pktlen

—ix_data

—ix_ctrl.os_buf_ptr

•IX_OSAL_CONVERT_IXPBUF_TO_OS_BUF(ixpBufPtr)

The following fields will get updated in the skbuffer

—(skb)osBufPtr = ix_ctrl.os_buf_ptr

—skb->data = IX_OSAL_MBUF_MDATA(ixMbufPtr)

—skb->len = IX_OSAL_MBUF_MLEN(ixMbufPtr)

—skb->len = IX_OSAL_MBUF_PKT_LEN(ixMbufPtr)

The suggested usage model of this function is:

•Allocate a pool of IXP_BUF buffer headers. Do not allocate data sections for these buffers.

•When passing a buffer from higher-level software (for example, OS network stack) to the IXP400 software, attach the skbuff to an IXP_BUF using the translation function.

•When receiving an IXP_BUF passed from the IXP400 software to higher-level software, use the translation function to retrieve a pointer to the skbuff that was attached to the IXP_BUF, and use that skbuff with the OS network stack to process the data.

The Intel® IXP400 Software Linux Ethernet Device driver (“ixp425_eth.c”), which is included in the IXP400 software distribution in form of a patch, contains an example of this suggested usage model.

April 2005	IXP400 Software Version 2.0	Programmer’s Guide
48	Document Number: 252539, Revision: 007