netdev - [PATCH net-next] bpf: add helper capable of reading out instructions

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Date:   Mon, 24 Jul 2017 14:22:36 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     netdev@...r.kernel.org
Cc:     daniel@...earbox.net, alexei.starovoitov@...il.com,
        oss-drivers@...ronome.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH net-next] bpf: add helper capable of reading out instructions

To read translated and jited instructions from the kernel,
one has to set certain pointers of struct bpf_prog_info to
pre-allocated user buffers.  Unfortunately, the existing
bpf_obj_get_info_by_fd() helper zeros struct bpf_prog_info
before passing it to the kernel.

Keeping the zeroing seems like a good idea in general, since
kernel will check if the structure was zeroed.  Add a new
helper for those more advanced users who can be trusted to
take care of zeroing themselves.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
I'm happy to change the name of the new function.

 tools/lib/bpf/bpf.c | 10 ++++++++--
 tools/lib/bpf/bpf.h |  2 ++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 412a7c82995a..2703fa282b65 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -308,13 +308,12 @@ int bpf_map_get_fd_by_id(__u32 id)
 	return sys_bpf(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
 }
 
-int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
+int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
 {
 	union bpf_attr attr;
 	int err;
 
 	bzero(&attr, sizeof(attr));
-	bzero(info, *info_len);
 	attr.info.bpf_fd = prog_fd;
 	attr.info.info_len = *info_len;
 	attr.info.info = ptr_to_u64(info);
@@ -325,3 +324,10 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
 
 	return err;
 }
+
+int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
+{
+	bzero(info, *info_len);
+
+	return __bpf_obj_get_info_by_fd(prog_fd, info, info_len);
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 418c86e69bcb..e44b423ac07e 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -58,6 +58,8 @@ int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id);
 int bpf_map_get_next_id(__u32 start_id, __u32 *next_id);
 int bpf_prog_get_fd_by_id(__u32 id);
 int bpf_map_get_fd_by_id(__u32 id);
+/* Note: bpf_obj_get_info_by_fd() will init info to zeroes */
 int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
+int __bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
 
 #endif
-- 
2.11.0