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>

7 files changed, 31 insertions, 2 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-map.rst b/tools/bpf/bpftool/Documentation/bpftool-map.rst
index 3221be1b9ccc..64b001b4f777 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-map.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-map.rst
@@ -128,6 +128,10 @@ OPTIONS
 	-f, --bpffs
 		  Show file names of pinned maps.
 
+	-n, --nomount
+		  Do not automatically attempt to mount any virtual file system
+		  (such as tracefs or BPF virtual file system) when necessary.
+
 EXAMPLES
 ========
 **# bpftool map show**
diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index 53920ffc48dd..58c8369b77dd 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -161,6 +161,10 @@ OPTIONS
 	-m, --mapcompat
 		  Allow loading maps with unknown map definitions.
 
+	-n, --nomount
+		  Do not automatically attempt to mount any virtual file system
+		  (such as tracefs or BPF virtual file system) when necessary.
+
 EXAMPLES
 ========
 **# bpftool prog show**
diff --git a/tools/bpf/bpftool/Documentation/bpftool.rst b/tools/bpf/bpftool/Documentation/bpftool.rst
index 129b7a9c0f9b..e1677e81ed59 100644
--- a/tools/bpf/bpftool/Documentation/bpftool.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool.rst
@@ -60,6 +60,10 @@ OPTIONS
 	-m, --mapcompat
 		  Allow loading maps with unknown map definitions.
 
+	-n, --nomount
+		  Do not automatically attempt to mount any virtual file system
+		  (such as tracefs or BPF virtual file system) when necessary.
+
 
 SEE ALSO
 ========
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';
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index 9e657e7d5172..f44a1c2c4ea0 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -24,6 +24,7 @@ json_writer_t *json_wtr;
 bool pretty_output;
 bool json_output;
 bool show_pinned;
+bool block_mount;
 int bpf_flags;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
@@ -313,6 +314,7 @@ int main(int argc, char **argv)
 		{ "version",	no_argument,	NULL,	'V' },
 		{ "bpffs",	no_argument,	NULL,	'f' },
 		{ "mapcompat",	no_argument,	NULL,	'm' },
+		{ "nomount",	no_argument,	NULL,	'n' },
 		{ 0 }
 	};
 	int opt, ret;
@@ -321,13 +323,14 @@ int main(int argc, char **argv)
 	pretty_output = false;
 	json_output = false;
 	show_pinned = false;
+	block_mount = false;
 	bin_name = argv[0];
 
 	hash_init(prog_table.table);
 	hash_init(map_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "Vhpjfm",
+	while ((opt = getopt_long(argc, argv, "Vhpjfmn",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -354,6 +357,9 @@ int main(int argc, char **argv)
 		case 'm':
 			bpf_flags = MAPS_RELAX_COMPAT;
 			break;
+		case 'n':
+			block_mount = true;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 9e4499c926fa..052c91d4dc55 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -44,7 +44,8 @@
 #define HELP_SPEC_PROGRAM						\
 	"PROG := { id PROG_ID | pinned FILE | tag PROG_TAG }"
 #define HELP_SPEC_OPTIONS						\
-	"OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} | {-m|--mapcompat}"
+	"OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} |\n"	\
+	"\t            {-m|--mapcompat} | {-n|--nomount} }"
 #define HELP_SPEC_MAP							\
 	"MAP := { id MAP_ID | pinned FILE }"
 
@@ -85,6 +86,7 @@ extern const char *bin_name;
 extern json_writer_t *json_wtr;
 extern bool json_output;
 extern bool show_pinned;
+extern bool block_mount;
 extern int bpf_flags;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;
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