bpf.2: Improvements after comments from Alexei Starovoitov

Reported-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/bpf.2

@@ -852,8 +852,6 @@ ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
 .fi
 .in
 .\"
-.\" FIXME 
-.\"
 .\"
 .SH EXAMPLES
 .\" FIXME It would be nice if this was a complete working example
@@ -895,8 +893,8 @@ main(int argc, char **argv)
                                 /* if (r0 == 0) goto pc+2 */
         BPF_MOV64_IMM(BPF_REG_1, 1),                /* r1 = 1 */
         BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0),
-.\" FIXME What does 'lock' in the line below mean?
                                 /* lock *(u64 *) r0 += r1 */
+.\"                                == atomic64_add
         BPF_MOV64_IMM(BPF_REG_0, 0),                /* r0 = 0 */
         BPF_EXIT_INSN(),                            /* return r0 */
     };
@@ -1054,13 +1052,16 @@ and similar calls.
 An eBPF object is deallocated only after all file descriptors
 referring to the object have been closed.
 
-eBPF programs can be written in a restricted C that is compiled into
-eBPF bytecode and executed on the in-kernel virtual machine or
+eBPF programs can be written in a restricted C that is compiled (using the
+.B clang
+compiler) into eBPF bytecode and executed on the in-kernel virtual machine or
 just-in-time compiled into native code.
 (Various features are omitted from this restricted C, such as loops, 
 global variables, variadic functions, floating-point numbers,
 and passing structures as function arguments.)
-.\" FIXME Add pointers to examples
+Some examples can be found in the
+.I samples/bpf/*_kern.c
+files in the kernel source tree.
 .\"       samples/bpf/*_kern.c + samples/bpf/Makefile ?
 .\" There are also examples for the tc classifier, in the iproute2
 .\" project, in examples/bpf