tools: bpftool: add an option to prevent auto-mount of bpffs, tracefs

In order to make life easier for users, bpftool automatically attempts
to mount the BPF virtual file system, if it is not mounted already,
before trying to pin objects in it. Similarly, it attempts to mount
tracefs if necessary before trying to dump the trace pipe to the
console.

While mounting file systems on-the-fly can improve user experience, some
administrators might prefer to avoid that. Let's add an option to block
these mount attempts. Note that it does not prevent automatic mounting
of tracefs by debugfs for the "bpftool prog tracelog" command.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/tracelog.c b/tools/bpf/bpftool/tracelog.c
index 2dc36dfa0896..e80a5c79b38f 100644
--- a/tools/bpf/bpftool/tracelog.c
+++ b/tools/bpf/bpftool/tracelog.c
@@ -91,6 +91,9 @@ static bool get_tracefs_pipe(char *mnt)
 	if (found && validate_tracefs_mnt(mnt, TRACEFS_MAGIC))
 		goto exit_found;
 
+	if (block_mount)
+		return false;
+
 	p_info("could not find tracefs, attempting to mount it now");
 	/* Most of the time, tracefs is automatically mounted by debugfs at
 	 * /sys/kernel/debug/tracing when we try to access it. If we could not