Maintain and observe a ZBUF_FLAG_IMMUTABLE flag on zero-copy BPF

buffer kernel descriptors, which is used to allow the buffer
currently in the BPF "store" position to be assigned to userspace
when it fills, even if userspace hasn't acknowledged the buffer
in the "hold" position yet.  To implement this, notify the buffer
model when a buffer becomes full, and check that the store buffer
is writable, not just for it being full, before trying to append
new packet data.  Shared memory buffers will be assigned to
userspace at most once per fill, be it in the store or in the
hold position.

This removes the restriction that at most one shared memory can
by owned by userspace, reducing the chances that userspace will
need to call select() after acknowledging one buffer in order to
wait for the next buffer when under high load.  This more fully
realizes the goal of zero system calls in order to process a
high-speed packet stream from BPF.

Update bpf.4 to reflect that both buffers may be owned by userspace
at once; caution against assuming this.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/net/bpf_zerocopy.h b/sys/net/bpf_zerocopy.h
index 33d1f25..92186a8 100644
--- a/sys/net/bpf_zerocopy.h
+++ b/sys/net/bpf_zerocopy.h
@@ -40,8 +40,10 @@ void	bpf_zerocopy_append_bytes(struct bpf_d *d, caddr_t buf, u_int offset,
 	    void *src, u_int len);
 void	bpf_zerocopy_append_mbuf(struct bpf_d *d, caddr_t buf, u_int offset,
 	    void *src, u_int len);
+void	bpf_zerocopy_buffull(struct bpf_d *);
 void	bpf_zerocopy_bufheld(struct bpf_d *);
 int	bpf_zerocopy_canfreebuf(struct bpf_d *);
+int	bpf_zerocopy_canwritebuf(struct bpf_d *);
 void	bpf_zerocopy_free(struct bpf_d *d);
 int	bpf_zerocopy_ioctl_getzmax(struct thread *td, struct bpf_d *d,
 	    size_t *i);