From: John Fastabend <john.fastab...@gmail.com> Date: Mon, 12 Mar 2018 12:23:34 -0700
> A single sendmsg or sendfile system call can contain multiple logical > messages that a BPF program may want to read and apply a verdict. But, > without an apply_bytes helper any verdict on the data applies to all > bytes in the sendmsg/sendfile. Alternatively, a BPF program may only > care to read the first N bytes of a msg. If the payload is large say > MB or even GB setting up and calling the BPF program repeatedly for > all bytes, even though the verdict is already known, creates > unnecessary overhead. > > To allow BPF programs to control how many bytes a given verdict > applies to we implement a bpf_msg_apply_bytes() helper. When called > from within a BPF program this sets a counter, internal to the > BPF infrastructure, that applies the last verdict to the next N > bytes. If the N is smaller than the current data being processed > from a sendmsg/sendfile call, the first N bytes will be sent and > the BPF program will be re-run with start_data pointing to the N+1 > byte. If N is larger than the current data being processed the > BPF verdict will be applied to multiple sendmsg/sendfile calls > until N bytes are consumed. > > Note1 if a socket closes with apply_bytes counter non-zero this > is not a problem because data is not being buffered for N bytes > and is sent as its received. > > Note2 if this is operating in the sendpage context the data > pointers may be zeroed after this call if the apply walks beyond > a msg_pull_data() call specified data range. (helper implemented > shortly in this series). > > Signed-off-by: John Fastabend <john.fastab...@gmail.com> Acked-by: David S. Miller <da...@davemloft.net>
