include/linux/shmem_fs.h

#ifndef __SHMEM_FS_H
#define __SHMEM_FS_H

/* inode in-kernel data */

#define SHMEM_NR_DIRECT 16

/*
 * A swap entry has to fit into a "unsigned long", as
 * the entry is hidden in the "index" field of the
 * swapper address space.
 *
 * We have to move it here, since not every user of fs.h is including
 * mm.h, but mm.h is including fs.h via sched .h :-/
 */
typedef struct {
	unsigned long val;
} swp_entry_t;

struct shmem_inode_info {
	spinlock_t		lock;
	unsigned long		next_index;
	swp_entry_t		i_direct[SHMEM_NR_DIRECT]; /* for the first blocks */
	void		      **i_indirect; /* indirect blocks */
	unsigned long		swapped;    /* data pages assigned to swap */
	unsigned long		flags;
	struct list_head	list;
	struct inode	       *inode;
};

struct shmem_sb_info {
	unsigned long max_blocks;   /* How many blocks are allowed */
	unsigned long free_blocks;  /* How many are left for allocation */
	unsigned long max_inodes;   /* How many inodes are allowed */
	unsigned long free_inodes;  /* How many are left for allocation */
	spinlock_t    stat_lock;
};

#define SHMEM_I(inode)  (&inode->u.shmem_i)

#endif