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      1 /*
      2  * Wrapper functions for accessing the file_struct fd array.
      3  */
      4 
      5 #ifndef __LINUX_FILE_H
      6 #define __LINUX_FILE_H
      7 
      8 #include <asm/atomic.h>
      9 #include <linux/posix_types.h>
     10 #include <linux/compiler.h>
     11 #include <linux/spinlock.h>
     12 #include <linux/rcupdate.h>
     13 #include <linux/types.h>
     14 
     15 /*
     16  * The default fd array needs to be at least BITS_PER_LONG,
     17  * as this is the granularity returned by copy_fdset().
     18  */
     19 #define NR_OPEN_DEFAULT BITS_PER_LONG
     20 
     21 /*
     22  * The embedded_fd_set is a small fd_set,
     23  * suitable for most tasks (which open <= BITS_PER_LONG files)
     24  */
     25 struct embedded_fd_set {
     26 	unsigned long fds_bits[1];
     27 };
     28 
     29 /*
     30  * More than this number of fds: we use a separately allocated fd_set
     31  */
     32 #define EMBEDDED_FD_SET_SIZE (BITS_PER_BYTE * sizeof(struct embedded_fd_set))
     33 
     34 struct fdtable {
     35 	unsigned int max_fds;
     36 	int max_fdset;
     37 	struct file ** fd;      /* current fd array */
     38 	fd_set *close_on_exec;
     39 	fd_set *open_fds;
     40 	struct rcu_head rcu;
     41 	struct files_struct *free_files;
     42 	struct fdtable *next;
     43 };
     44 
     45 /*
     46  * Open file table structure
     47  */
     48 struct files_struct {
     49   /*
     50    * read mostly part
     51    */
     52 	atomic_t count;
     53 	struct fdtable *fdt;
     54 	struct fdtable fdtab;
     55   /*
     56    * written part on a separate cache line in SMP
     57    */
     58 	spinlock_t file_lock ____cacheline_aligned_in_smp;
     59 	int next_fd;
     60 	struct embedded_fd_set close_on_exec_init;
     61 	struct embedded_fd_set open_fds_init;
     62 	struct file * fd_array[NR_OPEN_DEFAULT];
     63 };
     64 
     65 #define files_fdtable(files) (rcu_dereference((files)->fdt))
     66 
     67 extern void FASTCALL(__fput(struct file *));
     68 extern void FASTCALL(fput(struct file *));
     69 
     70 static inline void fput_light(struct file *file, int fput_needed)
     71 {
     72 	if (unlikely(fput_needed))
     73 		fput(file);
     74 }
     75 
     76 extern struct file * FASTCALL(fget(unsigned int fd));
     77 extern struct file * FASTCALL(fget_light(unsigned int fd, int *fput_needed));
     78 extern void FASTCALL(set_close_on_exec(unsigned int fd, int flag));
     79 extern void put_filp(struct file *);
     80 extern int get_unused_fd(void);
     81 extern void FASTCALL(put_unused_fd(unsigned int fd));
     82 struct kmem_cache;
     83 
     84 extern struct file ** alloc_fd_array(int);
     85 extern void free_fd_array(struct file **, int);
     86 
     87 extern fd_set *alloc_fdset(int);
     88 extern void free_fdset(fd_set *, int);
     89 
     90 extern int expand_files(struct files_struct *, int nr);
     91 extern void free_fdtable(struct fdtable *fdt);
     92 extern void __init files_defer_init(void);
     93 
     94 static inline struct file * fcheck_files(struct files_struct *files, unsigned int fd)
     95 {
     96 	struct file * file = NULL;
     97 	struct fdtable *fdt = files_fdtable(files);
     98 
     99 	if (fd < fdt->max_fds)
    100 		file = rcu_dereference(fdt->fd[fd]);
    101 	return file;
    102 }
    103 
    104 /*
    105  * Check whether the specified fd has an open file.
    106  */
    107 #define fcheck(fd)	fcheck_files(current->files, fd)
    108 
    109 extern void FASTCALL(fd_install(unsigned int fd, struct file * file));
    110 
    111 struct task_struct;
    112 
    113 struct files_struct *get_files_struct(struct task_struct *);
    114 void FASTCALL(put_files_struct(struct files_struct *fs));
    115 
    116 #endif /* __LINUX_FILE_H */
    117