bcachefs: add a quieter bch2_read_super

If we're looking for a bcachefs supers iteratively we don't want to see
this error.

This function replaces KERN_ERR with KERN_INFO for when we don't find a
bcachefs superblock but preserves other errors.
Signed-off-by: Daniel Hill <daniel@gluo.nz>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super-io.c

@@ -692,12 +692,13 @@ static int read_one_super(struct bch_sb_handle *sb, u64 offset, struct printbuf
 	return 0;
 }
 
-int bch2_read_super(const char *path, struct bch_opts *opts,
-		    struct bch_sb_handle *sb)
+static int __bch2_read_super(const char *path, struct bch_opts *opts,
+		    struct bch_sb_handle *sb, bool ignore_notbchfs_msg)
 {
 	u64 offset = opt_get(*opts, sb);
 	struct bch_sb_layout layout;
 	struct printbuf err = PRINTBUF;
+	struct printbuf err2 = PRINTBUF;
 	__le64 *i;
 	int ret;
 #ifndef __KERNEL__
@@ -760,8 +761,14 @@ int bch2_read_super(const char *path, struct bch_opts *opts,
 	if (opt_defined(*opts, sb))
 		goto err;
 
-	printk(KERN_ERR "bcachefs (%s): error reading default superblock: %s\n",
+	prt_printf(&err2, "bcachefs (%s): error reading default superblock: %s\n",
 	       path, err.buf);
+	if (ret == -BCH_ERR_invalid_sb_magic && ignore_notbchfs_msg)
+		printk(KERN_INFO "%s", err2.buf);
+	else
+		printk(KERN_ERR "%s", err2.buf);
+
+	printbuf_exit(&err2);
 	printbuf_reset(&err);
 
 	/*
@@ -837,6 +844,20 @@ int bch2_read_super(const char *path, struct bch_opts *opts,
 	goto out;
 }
 
+int bch2_read_super(const char *path, struct bch_opts *opts,
+		    struct bch_sb_handle *sb)
+{
+	return __bch2_read_super(path, opts, sb, false);
+}
+
+/* provide a silenced version for mount.bcachefs */
+
+int bch2_read_super_silent(const char *path, struct bch_opts *opts,
+		    struct bch_sb_handle *sb)
+{
+	return __bch2_read_super(path, opts, sb, true);
+}
+
 /* write superblock: */
 
 static void write_super_endio(struct bio *bio)

fs/bcachefs/super-io.h

@@ -84,6 +84,7 @@ void bch2_free_super(struct bch_sb_handle *);
 int bch2_sb_realloc(struct bch_sb_handle *, unsigned);
 
 int bch2_read_super(const char *, struct bch_opts *, struct bch_sb_handle *);
+int bch2_read_super_silent(const char *, struct bch_opts *, struct bch_sb_handle *);
 int bch2_write_super(struct bch_fs *);
 void __bch2_check_set_feature(struct bch_fs *, unsigned);