netdev - [PATCH v2 bpf-next 2/2] bpftool: Improve handling of ENOSPC on reuseport

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Date:   Fri, 12 Apr 2019 12:03:22 +0900
From:   Benjamin Poirier <bpoirier@...e.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v2 bpf-next 2/2] bpftool: Improve handling of ENOSPC on reuseport_array map dumps

avoids outputting a series of
	value:
	No space left on device

The value itself is not wrong but bpf_fd_reuseport_array_lookup_elem() can
only return it if the map was created with value_size = 8. There's nothing
bpftool can do about it. Instead of repeating this error for every key in
the map, print an explanatory warning and a specialized error.

example before:
key: 00 00 00 00
value:
No space left on device
key: 01 00 00 00
value:
No space left on device
key: 02 00 00 00
value:
No space left on device
Found 0 elements

example after:
Warning: cannot read values from reuseport_sockarray map with value_size != 8
key: 00 00 00 00  value: <cannot read>
key: 01 00 00 00  value: <cannot read>
key: 02 00 00 00  value: <cannot read>
Found 0 elements

Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
---
 tools/bpf/bpftool/map.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index 71840faaeab5..e6d72f777767 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -716,8 +716,12 @@ static int dump_map_elem(int fd, void *key, void *value,
 	} else {
 		const char *msg = NULL;
 
-		if (errno == ENOENT)
+		if (lookup_errno == ENOENT) {
 			msg = "<no entry>";
+		} else if (lookup_errno == ENOSPC && map_info->type ==
+			 BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
+			msg = "<cannot read>";
+		}
 
 		print_entry_error(map_info, key,
 				  msg ? : strerror(lookup_errno), !!msg);
@@ -774,6 +778,11 @@ static int do_dump(int argc, char **argv)
 			}
 		}
 
+	if (info.type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY &&
+	    info.value_size != 8) {
+		p_info("Warning: cannot read values from %s map with value_size != 8",
+		       map_type_name[info.type]);
+	}
 	while (true) {
 		err = bpf_map_get_next_key(fd, prev_key, key);
 		if (err) {
-- 
2.21.0