netdev - [RFC bpf-next 1/4] bpf: error handling when map_lookup

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Message-Id: <20180919075143.9308-2-bhole_prashant_q7@lab.ntt.co.jp>
Date:   Wed, 19 Sep 2018 16:51:40 +0900
From:   Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: [RFC bpf-next 1/4] bpf: error handling when map_lookup_elem isn't supported

The error value returned by map_lookup_elem doesn't differentiate
whether lookup was failed because of invalid key or lookup is not
supported.

Lets add handling for -EOPNOTSUPP return value of map_lookup_elem()
method of map, with expectation from map's implementation that it
should return -EOPNOTSUPP if lookup is not supported.

The errno for bpf syscall for BPF_MAP_LOOKUP_ELEM command will be set
to EOPNOTSUPP if map lookup is not supported.

Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
---
 kernel/bpf/syscall.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b3c2d09bcf7a..ecb06352b5a0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -716,10 +716,15 @@ static int map_lookup_elem(union bpf_attr *attr)
 	} else {
 		rcu_read_lock();
 		ptr = map->ops->map_lookup_elem(map, key);
-		if (ptr)
+		if (IS_ERR(ptr)) {
+			err = PTR_ERR(ptr);
+		} else if (!ptr) {
+			err = -ENOENT;
+		} else {
+			err = 0;
 			memcpy(value, ptr, value_size);
+		}
 		rcu_read_unlock();
-		err = ptr ? 0 : -ENOENT;
 	}
 
 	if (err)
-- 
2.17.1