netdev - Re: [RFC bpf-next] bpf: add new jited info fields in bpf_dev_offload and bpf_prog

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Date:   Thu, 11 Jan 2018 18:17:32 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     daniel@...earbox.net, alexei.starovoitov@...il.com, kafai@...com
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        francois.theron@...ronome.com,
        Jiong Wang <jiong.wang@...ronome.com>
Subject: Re: [RFC bpf-next] bpf: add new jited info fields in
 bpf_dev_offload and bpf_prog_info

On Thu, 11 Jan 2018 16:47:47 -0800, Jakub Kicinski wrote:
> Hi!
> 
> Jiong is working on dumping JITed NFP image via bpftool, Francois will be
> submitting support for NFP in binutils soon (whoop! :)).
> 
> We would appreciate if you could weigh in on the uAPI.  Is it OK to reuse
> the existing jited_prog_len/jited_prog_insns or should we add separate
> 2 new fields (plus the arch name) to avoid confusing old user space?

Ah, I skipped one chunk of Jiong's patch here, this would also be
necessary if we reuse fields:

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 2bac0dc..c7831cd 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1673,19 +1673,6 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 		goto done;
 	}
 
-	ulen = info.jited_prog_len;
-	info.jited_prog_len = prog->jited_len;
-	if (info.jited_prog_len && ulen) {
-		if (bpf_dump_raw_ok()) {
-			uinsns = u64_to_user_ptr(info.jited_prog_insns);
-			ulen = min_t(u32, info.jited_prog_len, ulen);
-			if (copy_to_user(uinsns, prog->bpf_func, ulen))
-				return -EFAULT;
-		} else {
-			info.jited_prog_insns = 0;
-		}
-	}
-
 	ulen = info.xlated_prog_len;
 	info.xlated_prog_len = bpf_prog_insn_size(prog);
 	if (info.xlated_prog_len && ulen) {
@@ -1711,6 +1698,21 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 		err = bpf_prog_offload_info_fill(&info, prog);
 		if (err)
 			return err;
+		else
+			goto done;
+	}
+
+	ulen = info.jited_prog_len;
+	info.jited_prog_len = prog->jited_len;
+	if (info.jited_prog_len && ulen) {
+		if (bpf_dump_raw_ok()) {
+			uinsns = u64_to_user_ptr(info.jited_prog_insns);
+			ulen = min_t(u32, info.jited_prog_len, ulen);
+			if (copy_to_user(uinsns, prog->bpf_func, ulen))
+				return -EFAULT;
+		} else {
+			info.jited_prog_insns = 0;
+		}
 	}
 
 done:

info.jited_prog_len is an in/out parameter, so we can't write it twice
if we share fields..  Sorry for messing up.