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, 6 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index 1bad6602a282..897483457bf0 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -177,6 +177,12 @@ int mount_bpffs_for_pin(const char *name)
 		/* nothing to do if already mounted */
 		goto out_free;
 
+	if (block_mount) {
+		p_err("no BPF file system found, not mounting it due to --nomount option");
+		err = -1;
+		goto out_free;
+	}
+
 	err = mnt_fs(dir, "bpf", err_str, ERR_MAX_LEN);
 	if (err) {
 		err_str[ERR_MAX_LEN - 1] = '\0';