ext4: show more binary mount options in procfs

Previously, /proc/fs/ext4/<dev>/options would only show binary options
if they were set (1 in the options bit mask). E.g. it would show "grpid"
if it was set, but it would not show "nogrpid" if grpid was not set.

This seems sensible, but when an option is absent from the file, it can
be hard for the unfamiliar to know what is being used. E.g. if there
isn't a (no)grpid entry, nogrpid is in effect. But if there isn't a
(no)auto_da_alloc entry, auto_da_alloc is in effect. If there isn't a
(minixdf|bsddf) entry, it turns out bsddf is in effect. It all depends
on how the option is implemented.

It's clearer to be explicit, so print the corresponding option
regardless of whether it means a 1 or a 0 in the bit mask.

Note that options which do not have an explicit disable option aren't
indicated as being disabled even with this change (e.g. dax).

Signed-off-by: Tyson Nottingham <tgnottingham@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -2021,7 +2021,7 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_super_block *es = sbi->s_es;
-	int def_errors, def_mount_opt = nodefs ? 0 : sbi->s_def_mount_opt;
+	int def_errors, def_mount_opt = sbi->s_def_mount_opt;
 	const struct mount_opts *m;
 	char sep = nodefs ? '\n' : ',';
 
@@ -2036,7 +2036,7 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 		if (((m->flags & (MOPT_SET|MOPT_CLEAR)) == 0) ||
 		    (m->flags & MOPT_CLEAR_ERR))
 			continue;
-		if (!(m->mount_opt & (sbi->s_mount_opt ^ def_mount_opt)))
+		if (!nodefs && !(m->mount_opt & (sbi->s_mount_opt ^ def_mount_opt)))
 			continue; /* skip if same as the default */
 		if ((want_set &&
 		     (sbi->s_mount_opt & m->mount_opt) != m->mount_opt) ||
@@ -2070,7 +2070,8 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 		SEQ_OPTS_PUTS("i_version");
 	if (nodefs || sbi->s_stripe)
 		SEQ_OPTS_PRINT("stripe=%lu", sbi->s_stripe);
-	if (EXT4_MOUNT_DATA_FLAGS & (sbi->s_mount_opt ^ def_mount_opt)) {
+	if (nodefs || EXT4_MOUNT_DATA_FLAGS &
+			(sbi->s_mount_opt ^ def_mount_opt)) {
 		if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA)
 			SEQ_OPTS_PUTS("data=journal");
 		else if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_ORDERED_DATA)