#ifndef __SHMEM_FS_H
  #define __SHMEM_FS_H

  #include <linux/file.h>

  #include <linux/swap.h>
  #include <linux/mempolicy.h>

  #include <linux/pagemap.h>

  #include <linux/percpu_counter.h>

  #include <linux/xattr.h>

  
  /* inode in-kernel data */

  struct shmem_inode_info {
  	spinlock_t		lock;

  	unsigned int		seals;		/* shmem seals */

  	unsigned long		flags;
  	unsigned long		alloced;	/* data pages alloced to file */

  	unsigned long		swapped;	/* subtotal assigned to swap */

  	struct list_head        shrinklist;     /* shrinkable hpage inodes */

  	struct list_head	swaplist;	/* chain of maybes on swap */

  	struct shared_policy	policy;		/* NUMA memory alloc policy */

  	struct simple_xattrs	xattrs;		/* list of xattrs */

  	struct inode		vfs_inode;
  };
  
  struct shmem_sb_info {
  	unsigned long max_blocks;   /* How many blocks are allowed */

  	struct percpu_counter used_blocks;  /* How many are allocated */

  	unsigned long max_inodes;   /* How many inodes are allowed */
  	unsigned long free_inodes;  /* How many are left for allocation */

  	spinlock_t stat_lock;	    /* Serialize shmem_sb_info changes */

  	umode_t mode;		    /* Mount mode for root directory */
  	unsigned char huge;	    /* Whether to try for hugepages */

  	kuid_t uid;		    /* Mount uid for root directory */
  	kgid_t gid;		    /* Mount gid for root directory */

  	struct mempolicy *mpol;     /* default memory policy for mappings */

  	spinlock_t shrinklist_lock;   /* Protects shrinklist */
  	struct list_head shrinklist;  /* List of shinkable inodes */
  	unsigned long shrinklist_len; /* Length of shrinklist */

  };
  
  static inline struct shmem_inode_info *SHMEM_I(struct inode *inode)
  {
  	return container_of(inode, struct shmem_inode_info, vfs_inode);
  }

  /*
   * Functions in mm/shmem.c called directly from elsewhere:
   */

  extern int shmem_init(void);

  extern int shmem_fill_super(struct super_block *sb, void *data, int silent);

  extern struct file *shmem_file_setup(const char *name,
  					loff_t size, unsigned long flags);

  extern struct file *shmem_kernel_file_setup(const char *name, loff_t size,
  					    unsigned long flags);

  extern int shmem_zero_setup(struct vm_area_struct *);

  extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
  		unsigned long len, unsigned long pgoff, unsigned long flags);

  extern int shmem_lock(struct file *file, int lock, struct user_struct *user);

  extern bool shmem_mapping(struct address_space *mapping);

  extern void shmem_unlock_mapping(struct address_space *mapping);

  extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
  					pgoff_t index, gfp_t gfp_mask);

  extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);

  extern int shmem_unuse(swp_entry_t entry, struct page *page);

  extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);

  extern unsigned long shmem_partial_swap_usage(struct address_space *mapping,
  						pgoff_t start, pgoff_t end);

  /* Flag allocation requirements to shmem_getpage */
  enum sgp_type {
  	SGP_READ,	/* don't exceed i_size, don't allocate page */
  	SGP_CACHE,	/* don't exceed i_size, may allocate page */
  	SGP_NOHUGE,	/* like SGP_CACHE, but no huge pages */
  	SGP_HUGE,	/* like SGP_CACHE, huge pages preferred */
  	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
  	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
  };
  
  extern int shmem_getpage(struct inode *inode, pgoff_t index,
  		struct page **pagep, enum sgp_type sgp);

  static inline struct page *shmem_read_mapping_page(
  				struct address_space *mapping, pgoff_t index)
  {
  	return shmem_read_mapping_page_gfp(mapping, index,
  					mapping_gfp_mask(mapping));
  }

  static inline bool shmem_file(struct file *file)
  {
  	if (!IS_ENABLED(CONFIG_SHMEM))
  		return false;
  	if (!file || !file->f_mapping)
  		return false;
  	return shmem_mapping(file->f_mapping);
  }

  extern bool shmem_charge(struct inode *inode, long pages);
  extern void shmem_uncharge(struct inode *inode, long pages);

  #ifdef CONFIG_TMPFS
  
  extern int shmem_add_seals(struct file *file, unsigned int seals);
  extern int shmem_get_seals(struct file *file);
  extern long shmem_fcntl(struct file *file, unsigned int cmd, unsigned long arg);
  
  #else
  
  static inline long shmem_fcntl(struct file *f, unsigned int c, unsigned long a)
  {
  	return -EINVAL;
  }
  
  #endif

  #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
  extern bool shmem_huge_enabled(struct vm_area_struct *vma);
  #else
  static inline bool shmem_huge_enabled(struct vm_area_struct *vma)
  {
  	return false;
  }
  #endif

  #endif