ext4: add interface to advertise ext4 features in sysfs

User-space should have the opportunity to check what features doest ext4
support in each particular copy. This adds easy interface by creating new
"features" directory in sys/fs/ext4/. In that directory files
advertising feature names can be created.

Add lazy_itable_init to the feature list.
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1574,6 +1574,11 @@ struct ext4_li_request {
 	unsigned long		lr_timeout;
 };
 
+struct ext4_features {
+	struct kobject f_kobj;
+	struct completion f_kobj_unregister;
+};
+
 /*
  * Function prototypes
  */

fs/ext4/ialloc.c

@@ -1274,6 +1274,16 @@ extern int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
 			    ext4_itable_unused_count(sb, gdp)),
 			    sbi->s_inodes_per_block);
 
+	if ((used_blks < 0) || (used_blks > sbi->s_itb_per_group)) {
+		ext4_error(sb, "Something is wrong with group %u\n"
+			   "Used itable blocks: %d"
+			   "itable unused count: %u\n",
+			   group, used_blks,
+			   ext4_itable_unused_count(sb, gdp));
+		ret = 1;
+		goto out;
+	}
+
 	blk = ext4_inode_table(sb, gdp) + used_blks;
 	num = sbi->s_itb_per_group - used_blks;
 
@@ -1283,15 +1293,6 @@ extern int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
 	if (ret)
 		goto err_out;
 
-	if (unlikely(num > EXT4_INODES_PER_GROUP(sb))) {
-		ext4_error(sb, "Something is wrong with group %u\n"
-			   "Used itable blocks: %d"
-			   "Itable blocks per group: %lu\n",
-			   group, used_blks, sbi->s_itb_per_group);
-		ret = 1;
-		goto err_out;
-	}
-
 	/*
 	 * Skip zeroout if the inode table is full. But we set the ZEROED
 	 * flag anyway, because obviously, when it is full it does not need

fs/ext4/super.c

@@ -57,6 +57,7 @@ struct proc_dir_entry *ext4_proc_root;
 static struct kset *ext4_kset;
 struct ext4_lazy_init *ext4_li_info;
 struct mutex ext4_li_mtx;
+struct ext4_features *ext4_feat;
 
 static int ext4_load_journal(struct super_block *, struct ext4_super_block *,
 			     unsigned long journal_devnum);
@@ -709,6 +710,7 @@ static void ext4_put_super(struct super_block *sb)
 	struct ext4_super_block *es = sbi->s_es;
 	int i, err;
 
+	ext4_unregister_li_request(sb);
 	dquot_disable(sb, -1, DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED);
 
 	flush_workqueue(sbi->dio_unwritten_wq);
@@ -727,7 +729,6 @@ static void ext4_put_super(struct super_block *sb)
 	}
 
 	del_timer(&sbi->s_err_report);
-	ext4_unregister_li_request(sb);
 	ext4_release_system_zone(sb);
 	ext4_mb_release(sb);
 	ext4_ext_release(sb);
@@ -2416,6 +2417,7 @@ static struct ext4_attr ext4_attr_##_name = {			\
 #define EXT4_ATTR(name, mode, show, store) \
 static struct ext4_attr ext4_attr_##name = __ATTR(name, mode, show, store)
 
+#define EXT4_INFO_ATTR(name) EXT4_ATTR(name, 0444, NULL, NULL)
 #define EXT4_RO_ATTR(name) EXT4_ATTR(name, 0444, name##_show, NULL)
 #define EXT4_RW_ATTR(name) EXT4_ATTR(name, 0644, name##_show, name##_store)
 #define EXT4_RW_ATTR_SBI_UI(name, elname)	\
@@ -2452,6 +2454,14 @@ static struct attribute *ext4_attrs[] = {
 	NULL,
 };
 
+/* Features this copy of ext4 supports */
+EXT4_INFO_ATTR(lazy_itable_init);
+
+static struct attribute *ext4_feat_attrs[] = {
+	ATTR_LIST(lazy_itable_init),
+	NULL,
+};
+
 static ssize_t ext4_attr_show(struct kobject *kobj,
 			      struct attribute *attr, char *buf)
 {
@@ -2480,7 +2490,6 @@ static void ext4_sb_release(struct kobject *kobj)
 	complete(&sbi->s_kobj_unregister);
 }
 
-
 static const struct sysfs_ops ext4_attr_ops = {
 	.show	= ext4_attr_show,
 	.store	= ext4_attr_store,
@@ -2492,6 +2501,17 @@ static struct kobj_type ext4_ktype = {
 	.release	= ext4_sb_release,
 };
 
+static void ext4_feat_release(struct kobject *kobj)
+{
+	complete(&ext4_feat->f_kobj_unregister);
+}
+
+static struct kobj_type ext4_feat_ktype = {
+	.default_attrs	= ext4_feat_attrs,
+	.sysfs_ops	= &ext4_attr_ops,
+	.release	= ext4_feat_release,
+};
+
 /*
  * Check whether this filesystem can be mounted based on
  * the features present and the RDONLY/RDWR mount requested.
@@ -4720,6 +4740,30 @@ static struct file_system_type ext4_fs_type = {
 	.fs_flags	= FS_REQUIRES_DEV,
 };
 
+int __init ext4_init_feat_adverts(void)
+{
+	struct ext4_features *ef;
+	int ret = -ENOMEM;
+
+	ef = kzalloc(sizeof(struct ext4_features), GFP_KERNEL);
+	if (!ef)
+		goto out;
+
+	ef->f_kobj.kset = ext4_kset;
+	init_completion(&ef->f_kobj_unregister);
+	ret = kobject_init_and_add(&ef->f_kobj, &ext4_feat_ktype, NULL,
+				   "features");
+	if (ret) {
+		kfree(ef);
+		goto out;
+	}
+
+	ext4_feat = ef;
+	ret = 0;
+out:
+	return ret;
+}
+
 static int __init init_ext4_fs(void)
 {
 	int err;
@@ -4732,6 +4776,9 @@ static int __init init_ext4_fs(void)
 	if (!ext4_kset)
 		goto out4;
 	ext4_proc_root = proc_mkdir("fs/ext4", NULL);
+
+	err = ext4_init_feat_adverts();
+
 	err = init_ext4_mballoc();
 	if (err)
 		goto out3;
@@ -4760,6 +4807,7 @@ static int __init init_ext4_fs(void)
 out2:
 	exit_ext4_mballoc();
 out3:
+	kfree(ext4_feat);
 	remove_proc_entry("fs/ext4", NULL);
 	kset_unregister(ext4_kset);
 out4: