bpf tools: Load a program with different instances using preprocessor
authorWang Nan <wangnan0@huawei.com>
Mon, 16 Nov 2015 12:10:09 +0000 (12:10 +0000)
committerArnaldo Carvalho de Melo <acme@redhat.com>
Wed, 18 Nov 2015 20:51:03 +0000 (17:51 -0300)
commitb580563e38487d9db8e94080149644da71c533c1
tree7c4f1b69a9b99706c1aaec7c818cb09221673b03
parent7d85c434214ea0b3416f7a62f76a0785b00d8797
bpf tools: Load a program with different instances using preprocessor

This patch is a preparation for BPF prologue support which allows
generating a series of BPF bytecode for fetching kernel data before
calling program code. With the newly introduced multiple instances
support, perf is able to create different prologues for different kprobe
points.

Before this patch, a bpf_program can be loaded into kernel only once,
and get the only resulting fd. What this patch does is to allow creating
and loading different variants of one bpf_program, then fetching their
fds.

Here we describe the basic idea in this patch. The detailed description
of the newly introduced APIs can be found in comments in the patch body.

The key of this patch is the new mechanism in bpf_program__load().
Instead of loading BPF program into kernel directly, it calls a
'pre-processor' to generate program instances which would be finally
loaded into the kernel based on the original code. To enable the
generation of multiple instances, libbpf passes an index to the
pre-processor so it know which instance is being loaded.

Pre-processor should be called from libbpf's user (perf) using
bpf_program__set_prep(). The number of instances and the relationship
between indices and the target instance should be clear when calling
bpf_program__set_prep().

To retrieve a fd for a specific instance of a program,
bpf_program__nth_fd() is introduced. It returns the resulting fd
according to index.

Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1447675815-166222-8-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
[ Enclosed multi-line if/else blocks with {}, (*func_ptr)() -> func_ptr() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
tools/lib/bpf/libbpf.c
tools/lib/bpf/libbpf.h