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From:   Bruno Meneguele <bmeneg@redhat.com>
To:     linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
        netdev@vger.kernel.org
Cc:     GLin@suse.com, davem@davemloft.net, kuba@kernel.org,
        ast@kernel.org, Bruno Meneguele <bmeneg@redhat.com>
Subject: [PATCH] net/bpfilter: fix dprintf usage for logging into /dev/kmsg
Date:   Thu, 12 Mar 2020 17:12:40 -0300
Message-Id: <20200312201240.1960367-1-bmeneg@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The bpfilter UMH code was recently changed to log its informative message=
s to
/dev/kmsg, however this interface doesn't support SEEK_CUR yet, used by
dprintf(). As result dprintf() returns -EINVAL and doesn't log anything.

Although there already had some discussions about supporting SEEK_CUR int=
o
/dev/kmsg in the past, it wasn't concluded. Considering the only
user of that interface from userspace perspective inside the kernel is th=
e
bpfilter UMH (userspace) module it's better to correct it here instead of
waiting a conclusion on the interface changes.

Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>
---
 net/bpfilter/main.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/bpfilter/main.c b/net/bpfilter/main.c
index 77396a098fbe..efea4874743e 100644
--- a/net/bpfilter/main.c
+++ b/net/bpfilter/main.c
@@ -10,7 +10,7 @@
 #include <asm/unistd.h>
 #include "msgfmt.h"
=20
-int debug_fd;
+FILE *debug_f;
=20
 static int handle_get_cmd(struct mbox_request *cmd)
 {
@@ -35,9 +35,10 @@ static void loop(void)
 		struct mbox_reply reply;
 		int n;
=20
+		fprintf(debug_f, "testing the buffer\n");
 		n =3D read(0, &req, sizeof(req));
 		if (n !=3D sizeof(req)) {
-			dprintf(debug_fd, "invalid request %d\n", n);
+			fprintf(debug_f, "invalid request %d\n", n);
 			return;
 		}
=20
@@ -47,7 +48,7 @@ static void loop(void)
=20
 		n =3D write(1, &reply, sizeof(reply));
 		if (n !=3D sizeof(reply)) {
-			dprintf(debug_fd, "reply failed %d\n", n);
+			fprintf(debug_f, "reply failed %d\n", n);
 			return;
 		}
 	}
@@ -55,9 +56,10 @@ static void loop(void)
=20
 int main(void)
 {
-	debug_fd =3D open("/dev/kmsg", 00000002);
-	dprintf(debug_fd, "Started bpfilter\n");
+	debug_f =3D fopen("/dev/kmsg", "w");
+	setvbuf(debug_f, 0, _IOLBF, 0);
+	fprintf(debug_f, "Started bpfilter\n");
 	loop();
-	close(debug_fd);
+	fclose(debug_f);
 	return 0;
 }
--=20
2.24.1