tools: bpftool: attempt to mount tracefs if required for tracelog cmd

As a follow-up to commit 30da46b5dc3a ("tools: bpftool: add a command to
dump the trace pipe"), attempt to mount the tracefs virtual file system
if it is not detected on the system before trying to dump content of the
tracing pipe on an invocation of "bpftool prog tracelog".

Usually, tracefs in automatically mounted by debugfs when the user tries
to access it (e.g. "ls /sys/kernel/debug/tracing" mounts the tracefs).
So if we failed to find it, it is probably that debugfs is not here
either. Therefore, we just attempt a single mount, at a location that
does not involve debugfs: /sys/kernel/tracing.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
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, 20 insertions, 5 deletions

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index 24582e8a96fb..1bad6602a282 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -76,7 +76,8 @@ void set_max_rlimit(void)
 	setrlimit(RLIMIT_MEMLOCK, &rinf);
 }
 
-static int mnt_bpffs(const char *target, char *buff, size_t bufflen)
+static int
+mnt_fs(const char *target, const char *type, char *buff, size_t bufflen)
 {
 	bool bind_done = false;
 
@@ -98,15 +99,29 @@ static int mnt_bpffs(const char *target, char *buff, size_t bufflen)
 		bind_done = true;
 	}
 
-	if (mount("bpf", target, "bpf", 0, "mode=0700")) {
-		snprintf(buff, bufflen, "mount -t bpf bpf %s failed: %s",
-			 target, strerror(errno));
+	if (mount(type, target, type, 0, "mode=0700")) {
+		snprintf(buff, bufflen, "mount -t %s %s %s failed: %s",
+			 type, type, target, strerror(errno));
 		return -1;
 	}
 
 	return 0;
 }
 
+int mount_tracefs(const char *target)
+{
+	char err_str[ERR_MAX_LEN];
+	int err;
+
+	err = mnt_fs(target, "tracefs", err_str, ERR_MAX_LEN);
+	if (err) {
+		err_str[ERR_MAX_LEN - 1] = '\0';
+		p_err("can't mount tracefs: %s", err_str);
+	}
+
+	return err;
+}
+
 int open_obj_pinned(char *path, bool quiet)
 {
 	int fd;
@@ -162,7 +177,7 @@ int mount_bpffs_for_pin(const char *name)
 		/* nothing to do if already mounted */
 		goto out_free;
 
-	err = mnt_bpffs(dir, err_str, ERR_MAX_LEN);
+	err = mnt_fs(dir, "bpf", err_str, ERR_MAX_LEN);
 	if (err) {
 		err_str[ERR_MAX_LEN - 1] = '\0';
 		p_err("can't mount BPF file system to pin the object (%s): %s",