On 7/2/25 6:57 PM, Song Yoong Siang wrote: [...]
+It is important to note that some devices may utilize the ``data_meta`` area for +their own purposes. For example, the IGC device utilizes ``IGC_TS_HDR_LEN`` +bytes of the ``data_meta`` area for receiving hardware timestamps. Therefore, +the XDP program should ensure that it does not overwrite any existing metadata. +The metadata layout of such device is depicted below::
- +----------+-----------------+--------------------------+------+
- | headroom | custom metadata | device-reserved metadata | data |
- +----------+-----------------+--------------------------+------+
^ ^| |- xdp_buff->data_meta xdp_buff->data
Imho, this section is misleading to developers. Suppose you're a XDP program writer and you want to implement a generic native BPF program (independent of the underlying NIC). Does this mean, the expectation is to dig into driver code to gather whether or not a driver is prepopulating and how much of it? What are the implications if the data is overwritten? For example, in Cilium today we use the buffer described here as device-reserved metadata and override it. How will users know what breaks?