bpftool: Support bpffs mountpoint as pin path for prog loadall

Currently, when using prog loadall and the pin path is a bpffs mountpoint,
bpffs will be repeatedly mounted to the parent directory of the bpffs
mountpoint path. For example, a `bpftool prog loadall test.o /sys/fs/bpf`
will trigger this.

Signed-off-by: Pengcheng Yang <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Quentin Monnet <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/bpf/bpftool/common.c

···
 	va_end(ap);
 }
 
-static bool is_bpffs(char *path)
+static bool is_bpffs(const char *path)
 {
 	struct statfs st_fs;
 
···
 	return fd;
 }
 
-int mount_bpffs_for_pin(const char *name)
+int mount_bpffs_for_pin(const char *name, bool is_dir)
 {
 	char err_str[ERR_MAX_LEN];
 	char *file;
 	char *dir;
 	int err = 0;
+
+	if (is_dir && is_bpffs(name))
+		return err;
 
 	file = malloc(strlen(name) + 1);
 	if (!file) {
···
 {
 	int err;
 
-	err = mount_bpffs_for_pin(name);
+	err = mount_bpffs_for_pin(name, false);
 	if (err)
 		return err;
 

tools/bpf/bpftool/iter.c

···
 		goto close_obj;
 	}
 
-	err = mount_bpffs_for_pin(path);
+	err = mount_bpffs_for_pin(path, false);
 	if (err)
 		goto close_link;
 

tools/bpf/bpftool/main.h

···
 char *get_fdinfo(int fd, const char *key);
 int open_obj_pinned(const char *path, bool quiet);
 int open_obj_pinned_any(const char *path, enum bpf_obj_type exp_type);
-int mount_bpffs_for_pin(const char *name);
+int mount_bpffs_for_pin(const char *name, bool is_dir);
 int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(int *, char ***));
 int do_pin_fd(int fd, const char *name);
 

tools/bpf/bpftool/prog.c

···
 		goto err_close_obj;
 	}
 
-	err = mount_bpffs_for_pin(pinfile);
+	err = mount_bpffs_for_pin(pinfile, !first_prog_only);
 	if (err)
 		goto err_close_obj;
 

tools/bpf/bpftool/struct_ops.c

···
 	if (argc == 1)
 		linkdir = GET_ARG();
 
-	if (linkdir && mount_bpffs_for_pin(linkdir)) {
+	if (linkdir && mount_bpffs_for_pin(linkdir, true)) {
 		p_err("can't mount bpffs for pinning");
 		return -1;
 	}