bcachefs: Make read_only a mount option again, but hidden

fsck passes read_only as a mount option, and it's required for
nochanges, which it also uses.

Usually read_only is handled by the VFS, but we need to be able to
handle it too; we just don't want to print it out twice, so mark it as a
hidden option.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/chardev.c

@@ -214,19 +214,6 @@ static long bch2_ioctl_fsck_offline(struct bch_ioctl_fsck_offline __user *user_a
 
 	if (arg.opts) {
 		char *optstr = strndup_user((char __user *)(unsigned long) arg.opts, 1 << 16);
-		char *ro, *rest;
-
-		/*
-		 * If passed a "read_only" mount option, remove it because it is
-		 * no longer a valid mount option, and the filesystem will be
-		 * set "read_only" regardless.
-		 */
-		ro = strstr(optstr, "read_only");
-		if (ro) {
-			rest = ro + strlen("read_only");
-			memmove(ro, rest, strlen(rest) + 1);
-		}
-
 		ret =   PTR_ERR_OR_ZERO(optstr) ?:
 			bch2_parse_mount_opts(NULL, &thr->opts, NULL, optstr);
 		if (!IS_ERR(optstr))

fs/bcachefs/fs.c

@@ -1800,7 +1800,8 @@ static int bch2_show_options(struct seq_file *seq, struct dentry *root)
 		const struct bch_option *opt = &bch2_opt_table[i];
 		u64 v = bch2_opt_get_by_id(&c->opts, i);
 
-		if (!(opt->flags & OPT_MOUNT))
+		if ((opt->flags & OPT_HIDDEN) ||
+		    !(opt->flags & OPT_MOUNT))
 			continue;
 
 		if (v == bch2_opt_get_by_id(&bch2_opts_default, i))

fs/bcachefs/opts.h

@@ -63,6 +63,7 @@ enum opt_flags {
 	OPT_MUST_BE_POW_2 = (1 << 7),	/* Must be power of 2 */
 	OPT_SB_FIELD_SECTORS = (1 << 8),/* Superblock field is >> 9 of actual value */
 	OPT_SB_FIELD_ILOG2 = (1 << 9),	/* Superblock field is ilog2 of actual value */
+	OPT_HIDDEN	= (1 << 10),
 };
 
 enum opt_type {
@@ -406,7 +407,7 @@ enum fsck_err_opts {
 	  BCH2_NO_SB_OPT,		BCH_SB_SECTOR,			\
 	  "offset",	"Sector offset of superblock")			\
 	x(read_only,			u8,				\
-	  OPT_FS,							\
+	  OPT_FS|OPT_MOUNT|OPT_HIDDEN,					\
 	  OPT_BOOL(),							\
 	  BCH2_NO_SB_OPT,		false,				\
 	  NULL,		NULL)						\