include/linux/fdtable.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * descriptor table internals; you almost certainly want file.h instead.
   4  */
   5
   6 #ifndef __LINUX_FDTABLE_H
   7 #define __LINUX_FDTABLE_H
   8
   9 #include <linux/posix_types.h>
  10 #include <linux/compiler.h>
  11 #include <linux/spinlock.h>
  12 #include <linux/rcupdate.h>
  13 #include <linux/nospec.h>
  14 #include <linux/types.h>
  15 #include <linux/init.h>
  16 #include <linux/fs.h>
  17
  18 #include <linux/atomic.h>
  19
  20 /*
  21  * The default fd array needs to be at least BITS_PER_LONG,
  22  * as this is the granularity returned by copy_fdset().
  23  */
  24 #define NR_OPEN_DEFAULT BITS_PER_LONG
  25
  26 struct fdtable {
  27         unsigned int max_fds;
  28         struct file __rcu **fd;      /* current fd array */
  29         unsigned long *close_on_exec;
  30         unsigned long *open_fds;
  31         unsigned long *full_fds_bits;
  32         struct rcu_head rcu;
  33 };
  34
  35 static inline bool close_on_exec(unsigned int fd, const struct fdtable *fdt)
  36 {
  37         return test_bit(fd, fdt->close_on_exec);
  38 }
  39
  40 static inline bool fd_is_open(unsigned int fd, const struct fdtable *fdt)
  41 {
  42         return test_bit(fd, fdt->open_fds);
  43 }
  44
  45 /*
  46  * Open file table structure
  47  */
  48 struct files_struct {
  49   /*
  50    * read mostly part
  51    */
  52         atomic_t count;
  53         bool resize_in_progress;
  54         wait_queue_head_t resize_wait;
  55
  56         struct fdtable __rcu *fdt;
  57         struct fdtable fdtab;
  58   /*
  59    * written part on a separate cache line in SMP
  60    */
  61         spinlock_t file_lock ____cacheline_aligned_in_smp;
  62         unsigned int next_fd;
  63         unsigned long close_on_exec_init[1];
  64         unsigned long open_fds_init[1];
  65         unsigned long full_fds_bits_init[1];
  66         struct file __rcu * fd_array[NR_OPEN_DEFAULT];
  67 };
  68
  69 struct file_operations;
  70 struct vfsmount;
  71 struct dentry;
  72
  73 #define rcu_dereference_check_fdtable(files, fdtfd) \
  74         rcu_dereference_check((fdtfd), lockdep_is_held(&(files)->file_lock))
  75
  76 #define files_fdtable(files) \
  77         rcu_dereference_check_fdtable((files), (files)->fdt)
  78
  79 /*
  80  * The caller must ensure that fd table isn't shared or hold rcu or file lock
  81  */
  82 static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd)
  83 {
  84         struct fdtable *fdt = rcu_dereference_raw(files->fdt);
  85
  86         if (fd < fdt->max_fds) {
  87                 fd = array_index_nospec(fd, fdt->max_fds);
  88                 return rcu_dereference_raw(fdt->fd[fd]);
  89         }
  90         return NULL;
  91 }
  92
  93 static inline struct file *fcheck_files(struct files_struct *files, unsigned int fd)
  94 {
  95         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
  96                            !lockdep_is_held(&files->file_lock),
  97                            "suspicious rcu_dereference_check() usage");
  98         return __fcheck_files(files, fd);
  99 }
 100
 101 /*
 102  * Check whether the specified fd has an open file.
 103  */
 104 #define fcheck(fd)      fcheck_files(current->files, fd)
 105
 106 struct task_struct;
 107
 108 struct files_struct *get_files_struct(struct task_struct *);
 109 void put_files_struct(struct files_struct *fs);
 110 void reset_files_struct(struct files_struct *);
 111 int unshare_files(struct files_struct **);
 112 struct files_struct *dup_fd(struct files_struct *, int *) __latent_entropy;
 113 void do_close_on_exec(struct files_struct *);
 114 int iterate_fd(struct files_struct *, unsigned,
 115                 int (*)(const void *, struct file *, unsigned),
 116                 const void *);
 117
 118 extern int __alloc_fd(struct files_struct *files,
 119                       unsigned start, unsigned end, unsigned flags);
 120 extern void __fd_install(struct files_struct *files,
 121                       unsigned int fd, struct file *file);
 122 extern int __close_fd(struct files_struct *files,
 123                       unsigned int fd);
 124
 125 extern struct kmem_cache *files_cachep;
 126
 127 #endif /* __LINUX_FDTABLE_H */