tools: bpftool: pass an argument to silence open_obj_pinned()

Function open_obj_pinned() prints error messages when it fails to open a
link in the BPF virtual file system. However, in some occasions it is
not desirable to print an error, for example when we parse all links
under the bpffs root, and the error is due to some paths actually being
symbolic links.

Example output:

    # ls -l /sys/fs/bpf/
    lrwxrwxrwx 1 root root 0 Oct 18 19:00 ip -> /sys/fs/bpf/tc/
    drwx------ 3 root root 0 Oct 18 19:00 tc
    lrwxrwxrwx 1 root root 0 Oct 18 19:00 xdp -> /sys/fs/bpf/tc/

    # bpftool --bpffs prog show
    Error: bpf obj get (/sys/fs/bpf): Permission denied
    Error: bpf obj get (/sys/fs/bpf): Permission denied

    # strace -e bpf bpftool --bpffs prog show
    bpf(BPF_OBJ_GET, {pathname="/sys/fs/bpf/ip", bpf_fd=0}, 72) = -1 EACCES (Permission denied)
    Error: bpf obj get (/sys/fs/bpf): Permission denied
    bpf(BPF_OBJ_GET, {pathname="/sys/fs/bpf/xdp", bpf_fd=0}, 72) = -1 EACCES (Permission denied)
    Error: bpf obj get (/sys/fs/bpf): Permission denied
    ...

To fix it, pass a bool as a second argument to the function, and prevent
it from printing an error when the argument is set to true.

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>

tools/bpf/bpftool/common.c

@@ -130,16 +130,17 @@ static int mnt_bpffs(const char *target, char *buff, size_t bufflen)
 	return 0;
 }
 
-int open_obj_pinned(char *path)
+int open_obj_pinned(char *path, bool quiet)
 {
 	int fd;
 
 	fd = bpf_obj_get(path);
 	if (fd < 0) {
-		p_err("bpf obj get (%s): %s", path,
-		      errno == EACCES && !is_bpffs(dirname(path)) ?
-		    "directory not in bpf file system (bpffs)" :
-		    strerror(errno));
+		if (!quiet)
+			p_err("bpf obj get (%s): %s", path,
+			      errno == EACCES && !is_bpffs(dirname(path)) ?
+			    "directory not in bpf file system (bpffs)" :
+			    strerror(errno));
 		return -1;
 	}
 
@@ -151,7 +152,7 @@ int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type)
 	enum bpf_obj_type type;
 	int fd;
 
-	fd = open_obj_pinned(path);
+	fd = open_obj_pinned(path, false);
 	if (fd < 0)
 		return -1;
 
@@ -384,7 +385,7 @@ int build_pinned_obj_table(struct pinned_obj_table *tab,
 		while ((ftse = fts_read(fts))) {
 			if (!(ftse->fts_info & FTS_F))
 				continue;
-			fd = open_obj_pinned(ftse->fts_path);
+			fd = open_obj_pinned(ftse->fts_path, true);
 			if (fd < 0)
 				continue;
 

tools/bpf/bpftool/main.h

@@ -127,7 +127,7 @@ int cmd_select(const struct cmd *cmds, int argc, char **argv,
 int get_fd_type(int fd);
 const char *get_fd_type_name(enum bpf_obj_type type);
 char *get_fdinfo(int fd, const char *key);
-int open_obj_pinned(char *path);
+int open_obj_pinned(char *path, bool quiet);
 int open_obj_pinned_any(char *path, enum bpf_obj_type exp_type);
 int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(__u32));
 int do_pin_fd(int fd, const char *name);