ファイルシステムの抽象化をしたオブジェクトが super_block です。

　より正確に言うとファイルシステムに関するグローバル情報を保持しています。

　全部ではないですがメンバーオブジェクト・メンバー変数はヘッダーから以下のように確認できます。

// /usr/src/linux-headers-4.18.16-041816-generic/include/linux/fs.h
1348 struct super_block {
1349   struct list_head  s_list;   /* Keep this first */
1350   dev_t     s_dev;    /* search index; _not_ kdev_t */
1351   unsigned char   s_blocksize_bits;
1352   unsigned long   s_blocksize;
1353   loff_t      s_maxbytes; /* Max file size */
1354   struct file_system_type *s_type;
1355   const struct super_operations *s_op;
1356   const struct dquot_operations *dq_op;
1357   const struct quotactl_ops *s_qcop;
1358   const struct export_operations *s_export_op;
1359   unsigned long   s_flags;
1360   unsigned long   s_iflags; /* internal SB_I_* flags */
1361   unsigned long   s_magic;
1362   struct dentry   *s_root;
1363   struct rw_semaphore s_umount;
1364   int     s_count;
1365   atomic_t    s_active;
1366 #ifdef CONFIG_SECURITY
1367   void                    *s_security;
1368 #endif
1369   const struct xattr_handler **s_xattr;
1370 #if IS_ENABLED(CONFIG_FS_ENCRYPTION)
1371   const struct fscrypt_operations *s_cop;
1372 #endif
1373   struct hlist_bl_head  s_roots;  /* alternate root dentries for NFS */
1374   struct list_head  s_mounts; /* list of mounts; _not_ for fs use */
1375   struct block_device *s_bdev;
1376   struct backing_dev_info *s_bdi;
1377   struct mtd_info   *s_mtd;
1378   struct hlist_node s_instances;
1379   unsigned int    s_quota_types;  /* Bitmask of supported quota types */
1380   struct quota_info s_dquot;  /* Diskquota specific options */
1381
1382   struct sb_writers s_writers;
1383
1384   char      s_id[32]; /* Informational name */
1385   uuid_t      s_uuid;   /* UUID */
1386
1387   void      *s_fs_info; /* Filesystem private info */
1388   unsigned int    s_max_links;
1389   fmode_t     s_mode;

　蛇足ですがメンバーとして宣言されている super_operations は関数ポインターを宣言しています。

// /usr/src/linux-headers-4.18.16-041816-generic/include/linux/fs.h
1824 struct super_operations {
1825     struct inode *(*alloc_inode)(struct super_block *sb);
1826   void (*destroy_inode)(struct inode *);
1827
1828     void (*dirty_inode) (struct inode *, int flags);
1829   int (*write_inode) (struct inode *, struct writeback_control *wbc);
1830   int (*drop_inode) (struct inode *);
1831   void (*evict_inode) (struct inode *);
1832   void (*put_super) (struct super_block *);
1833   int (*sync_fs)(struct super_block *sb, int wait);
1834   int (*freeze_super) (struct super_block *);
1835   int (*freeze_fs) (struct super_block *);
1836   int (*thaw_super) (struct super_block *);
1837   int (*unfreeze_fs) (struct super_block *);
1838   int (*statfs) (struct dentry *, struct kstatfs *);
1839   int (*remount_fs) (struct super_block *, int *, char *);
1840   void (*umount_begin) (struct super_block *);
1841
1842   int (*show_options)(struct seq_file *, struct dentry *);
1843   int (*show_devname)(struct seq_file *, struct dentry *);
1844   int (*show_path)(struct seq_file *, struct dentry *);
1845   int (*show_stats)(struct seq_file *, struct dentry *);
1846 #ifdef CONFIG_QUOTA
1847   ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
1848   ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, l
1849   struct dquot **(*get_dquots)(struct inode *);
1850 #endif
1851   int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
1852   long (*nr_cached_objects)(struct super_block *,
1853           struct shrink_control *);
1854   long (*free_cached_objects)(struct super_block *,
1855             struct shrink_control *);
1856 };

　この中で重要なのは inode 系の関数です。

　覚えておくと良さそうのは alloc_inode / destroy_inode / dirty_inode / write_inode / put_super / sync_fs / statfs あたりでしょうかね。