[PATCH bpf-next v4 4/6] libbpf: Use pr_warn() when printing netlink errors

["Toke Høiland-Jørgensen" <toke@redhat.com>]

From: Toke Høiland-Jørgensen <toke@redhat.com>

The netlink functions were using fprintf(stderr, ) directly to print out
error messages, instead of going through the usual logging macros. This
makes it impossible for the calling application to silence or redirect
those error messages. Fix this by switching to pr_warn() in nlattr.c and
netlink.c.

Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/netlink.c |    3 ++-
 tools/lib/bpf/nlattr.c  |   10 +++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index ce3ec81b71c0..a261df9cb488 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -12,6 +12,7 @@
 
 #include "bpf.h"
 #include "libbpf.h"
+#include "libbpf_internal.h"
 #include "nlattr.h"
 
 #ifndef SOL_NETLINK
@@ -43,7 +44,7 @@ int libbpf_netlink_open(__u32 *nl_pid)
 
 	if (setsockopt(sock, SOL_NETLINK, NETLINK_EXT_ACK,
 		       &one, sizeof(one)) < 0) {
-		fprintf(stderr, "Netlink error reporting not supported\n");
+		pr_warn("Netlink error reporting not supported\n");
 	}
 
 	if (bind(sock, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
diff --git a/tools/lib/bpf/nlattr.c b/tools/lib/bpf/nlattr.c
index 1e69c0c8d413..8db44bbfc66d 100644
--- a/tools/lib/bpf/nlattr.c
+++ b/tools/lib/bpf/nlattr.c
@@ -8,6 +8,7 @@
 
 #include <errno.h>
 #include "nlattr.h"
+#include "libbpf_internal.h"
 #include <linux/rtnetlink.h>
 #include <string.h>
 #include <stdio.h>
@@ -121,8 +122,8 @@ int libbpf_nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head,
 		}
 
 		if (tb[type])
-			fprintf(stderr, "Attribute of type %#x found multiple times in message, "
-				  "previous attribute is being ignored.\n", type);
+			pr_warn("Attribute of type %#x found multiple times in message, "
+				"previous attribute is being ignored.\n", type);
 
 		tb[type] = nla;
 	}
@@ -181,15 +182,14 @@ int libbpf_nla_dump_errormsg(struct nlmsghdr *nlh)
 
 	if (libbpf_nla_parse(tb, NLMSGERR_ATTR_MAX, attr, alen,
 			     extack_policy) != 0) {
-		fprintf(stderr,
-			"Failed to parse extended error attributes\n");
+		pr_warn("Failed to parse extended error attributes\n");
 		return 0;
 	}
 
 	if (tb[NLMSGERR_ATTR_MSG])
 		errmsg = (char *) libbpf_nla_data(tb[NLMSGERR_ATTR_MSG]);
 
-	fprintf(stderr, "Kernel error message: %s\n", errmsg);
+	pr_warn("Kernel error message: %s\n", errmsg);
 
 	return 0;
 }