fat: Convert to new mount api

vfat and msdos share a common set of options, with additional, unique
options for each filesystem.

Each filesystem calls common fc initialization and parsing routines,
with an "is_vfat" parameter. For parsing, if the option is not found
in the common parameter_spec, parsing is retried with the fs-specific
parameter_spec.

This patch leaves nls loading to fill_super, so the codepage and charset
options are not validated as they are requested. This matches current
behavior. It would be possible to test-load as each option is parsed,
but that would make i.e.

mount -o "iocharset=nope,iocharset=iso8859-1"

fail, where it does not fail today because only the last iocharset
option is considered.

The obsolete "conv=" option is set up with an enum of acceptable values;
currently invalid "conv=" options are rejected as such, even though the
option is obsolete, so this patch preserves that behavior.

Signed-off-by: Eric Sandeen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: OGAWA Hirofumi <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: Eric Sandeen

fs/fat/fat.h

@@ -7,6 +7,8 @@
 #include <linux/hash.h>
 #include <linux/ratelimit.h>
 #include <linux/msdos_fs.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
 
 /*
  * vfat shortname flags
@@ -416,12 +418,21 @@ extern struct inode *fat_iget(struct super_block *sb, loff_t i_pos);
 extern struct inode *fat_build_inode(struct super_block *sb,
 			struct msdos_dir_entry *de, loff_t i_pos);
 extern int fat_sync_inode(struct inode *inode);
-extern int fat_fill_super(struct super_block *sb, void *data, int silent,
-			  int isvfat, void (*setup)(struct super_block *));
+extern int fat_fill_super(struct super_block *sb, struct fs_context *fc,
+			  void (*setup)(struct super_block *));
 extern int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de);
 
 extern int fat_flush_inodes(struct super_block *sb, struct inode *i1,
 			    struct inode *i2);
+
+extern const struct fs_parameter_spec fat_param_spec[];
+int fat_init_fs_context(struct fs_context *fc, bool is_vfat);
+void fat_free_fc(struct fs_context *fc);
+
+int fat_parse_param(struct fs_context *fc, struct fs_parameter *param,
+		    bool is_vfat);
+int fat_reconfigure(struct fs_context *fc);
+
 static inline unsigned long fat_dir_hash(int logstart)
 {
 	return hash_32(logstart, FAT_HASH_BITS);