Add kfunc bpf_xdp_pull_data #5981
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Move skb_frag_t adjustment into bpf_xdp_shrink_data() and extend its functionality to be able to shrink an xdp fragment from both head and tail. In a later patch, bpf_xdp_pull_data() will reuse it to shrink an xdp fragment from head. Additionally, in bpf_xdp_frags_shrink_tail(), breaking the loop when bpf_xdp_shrink_data() returns false (i.e., not releasing the current fragment) is not necessary as the loop condition, offset > 0, has the same effect. Remove the else branch to simplify the code. Signed-off-by: Amery Hung <[email protected]>
Add kfunc, bpf_xdp_pull_data(), to support pulling data from xdp fragments. Similar to bpf_skb_pull_data(), bpf_xdp_pull_data() makes the first len bytes of data directly readable and writable in bpf programs. If the "len" argument is larger than the linear data size, data in fragments will be copied to the linear data area when there is enough room. Specifically, the kfunc will try to use the tailroom first. When the tailroom is not enough, metadata and data will be shifted down to make room for pulling data. A use case of the kfunc is to decapsulate headers residing in xdp fragments. It is possible for a NIC driver to place headers in xdp fragments. To keep using direct packet access for parsing and decapsulating headers, users can pull headers into the linear data area by calling bpf_xdp_pull_data() and then pop the header with bpf_xdp_adjust_head(). Reviewed-by: Jakub Kicinski <[email protected]> Signed-off-by: Amery Hung <[email protected]>
bpf_xdp_pull_data() may change packet data and therefore packet pointers need to be invalidated. Add bpf_xdp_pull_data() to the special kfunc list instead of introducing a new KF_ flag until there are more kfuncs changing packet data. Signed-off-by: Amery Hung <[email protected]>
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Upstream branch: 3547a61 |
…_RUN To test bpf_xdp_pull_data(), an xdp packet containing fragments as well as free linear data area after xdp->data_end needs to be created. However, bpf_prog_test_run_xdp() always fills the linear area with data_in before creating fragments, leaving no space to pull data. This patch will allow users to specify the linear data size through ctx->data_end. Currently, ctx_in->data_end must match data_size_in and will not be the final ctx->data_end seen by xdp programs. This is because ctx->data_end is populated according to the xdp_buff passed to test_run. The linear data area available in an xdp_buff, max_data_sz, is alawys filled up before copying data_in into fragments. This patch will allow users to specify the size of data that goes into the linear area. When ctx_in->data_end is different from data_size_in, only ctx_in->data_end bytes of data will be put into the linear area when creating the xdp_buff. While ctx_in->data_end will be allowed to be different from data_size_in, it cannot be larger than the data_size_in as there will be no data to copy from user space. If it is larger than the maximum linear data area size, the layout suggested by the user will not be honored. Data beyond max_data_sz bytes will still be copied into fragments. Finally, since it is possible for a NIC to produce a xdp_buff with empty linear data area, allow it when calling bpf_test_init() from bpf_prog_test_run_xdp() so that we can test XDP kfuncs with such xdp_buff. This is done by moving lower-bound check to callers as most of them already do except bpf_prog_test_run_skb(). Signed-off-by: Amery Hung <[email protected]>
Test bpf_xdp_pull_data() with xdp packets with different layouts. The xdp bpf program first checks if the layout is as expected. Then, it calls bpf_xdp_pull_data(). Finally, it checks the 0xbb marker at offset 1024 using directly packet access. Signed-off-by: Amery Hung <[email protected]>
It is possible for drivers to generate xdp packets with data residing entirely in fragments. To keep parsing headers using direcy packet access, call bpf_xdp_pull_data() to pull headers into the linear data area. Signed-off-by: Amery Hung <[email protected]>
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Pull request for series with
subject: Add kfunc bpf_xdp_pull_data
version: 4
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1003547