bcachefs: fix the error code when mounting with incorrect options.

When mount with incorrect options such as:
"mount -t bcachefs -o errors=back /dev/loop1 /mnt/bcachefs/".
It rebacks the error "mount: /mnt/bcachefs: permission denied."
 cause bch2_parse_mount_opts returns -1 and bch2_mount throws
it up. This is unreasonable.

The real error message should be like this:
"mount: /mnt/bcachefs: wrong fs type, bad option, bad
superblock on /dev/loop1, missing codepage or helper program,
or other error."

Adding three private error codes for mounting error. Here are:
  - BCH_ERR_mount_option as the parent class for option error.
  - BCH_ERR_option_name represents the invalid option name.
  - BCH_ERR_option_value represents the invalid option value.
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/errcode.h

@@ -5,6 +5,9 @@
 #define BCH_ERRCODES()								\
 	x(ERANGE,			ERANGE_option_too_small)		\
 	x(ERANGE,			ERANGE_option_too_big)			\
+	x(EINVAL,			mount_option)				\
+	x(BCH_ERR_mount_option,		option_name)				\
+	x(BCH_ERR_mount_option,		option_value)				\
 	x(ENOMEM,			ENOMEM_stripe_buf)			\
 	x(ENOMEM,			ENOMEM_replicas_table)			\
 	x(ENOMEM,			ENOMEM_cpu_replicas)			\

fs/bcachefs/fs.c

@@ -1870,8 +1870,10 @@ static struct dentry *bch2_mount(struct file_system_type *fs_type,
 	opt_set(opts, read_only, (flags & SB_RDONLY) != 0);
 
 	ret = bch2_parse_mount_opts(NULL, &opts, data);
-	if (ret)
+	if (ret) {
+		ret = bch2_err_class(ret);
 		return ERR_PTR(ret);
+	}
 
 	if (!dev_name || strlen(dev_name) == 0)
 		return ERR_PTR(-EINVAL);

fs/bcachefs/opts.c

@@ -456,7 +456,7 @@ int bch2_parse_mount_opts(struct bch_fs *c, struct bch_opts *opts,
 
 	copied_opts = kstrdup(options, GFP_KERNEL);
 	if (!copied_opts)
-		return -1;
+		return -ENOMEM;
 	copied_opts_start = copied_opts;
 
 	while ((opt = strsep(&copied_opts, ",")) != NULL) {
@@ -501,11 +501,11 @@ int bch2_parse_mount_opts(struct bch_fs *c, struct bch_opts *opts,
 
 bad_opt:
 	pr_err("Bad mount option %s", name);
-	ret = -1;
+	ret = -BCH_ERR_option_name;
 	goto out;
 bad_val:
 	pr_err("Invalid mount option %s", err.buf);
-	ret = -1;
+	ret = -BCH_ERR_option_value;
 	goto out;
 out:
 	kfree(copied_opts_start);