include/linux/file.h

   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 extern void _fput(struct file *);
   9
  10 /*
  11  * Check whether the specified task has the fd open. Since the task
  12  * may not have a files_struct, we must test for p->files != NULL.
  13  */
  14 extern inline struct file * fcheck_task(struct task_struct *p, unsigned int fd)
  15 {
  16         struct file * file = NULL;
  17
  18         if (fd < p->files->max_fds)
  19                 file = p->files->fd[fd];
  20         return file;
  21 }
  22
  23 /*
  24  * Check whether the specified fd has an open file.
  25  */
  26 extern inline struct file * fcheck(unsigned int fd)
  27 {
  28         struct file * file = NULL;
  29         struct files_struct *files = current->files;
  30
  31         if (fd < files->max_fds)
  32                 file = files->fd[fd];
  33         return file;
  34 }
  35
  36 extern inline struct file * frip(unsigned int fd)
  37 {
  38         struct file * file = NULL;
  39
  40         if (fd < current->files->max_fds)
  41                 file = xchg(&current->files->fd[fd], NULL);
  42         return file;
  43 }
  44
  45 extern inline struct file * fget(unsigned int fd)
  46 {
  47         struct file * file = NULL;
  48         struct files_struct *files = current->files;
  49
  50         read_lock(&files->file_lock);
  51         file = fcheck(fd);
  52         if (file)
  53                 get_file(file);
  54         read_unlock(&files->file_lock);
  55         return file;
  56 }
  57
  58 /*
  59  * 23/12/1998 Marcin Dalecki <dalecki@cs.net.pl>:
  60  *
  61  * Since those functions where calling other functions, it was compleatly
  62  * bogous to make them all "extern inline".
  63  *
  64  * The removal of this pseudo optimization saved me scandaleous:
  65  *
  66  *              3756 (i386 arch)
  67  *
  68  * precious bytes from my kernel, even without counting all the code compiled
  69  * as module!
  70  *
  71  * I suspect there are many other similar "optimizations" across the
  72  * kernel...
  73  */
  74 extern inline void fput(struct file * file)
  75 {
  76         if (atomic_dec_and_test(&file->f_count))
  77                 _fput(file);
  78 }
  79 extern void put_filp(struct file *);
  80
  81 /*
  82  * Install a file pointer in the fd array.
  83  *
  84  * The VFS is full of places where we drop the files lock between
  85  * setting the open_fds bitmap and installing the file in the file
  86  * array.  At any such point, we are vulnerable to a dup2() race
  87  * installing a file in the array before us.  We need to detect this and
  88  * fput() the struct file we are about to overwrite in this case.
  89  */
  90
  91 extern inline void fd_install(unsigned int fd, struct file * file)
  92 {
  93         struct files_struct *files = current->files;
  94         struct file * result;
  95
  96         write_lock(&files->file_lock);
  97         result = xchg(&files->fd[fd], file);
  98         write_unlock(&files->file_lock);
  99         if (result)
 100                 fput(result);
 101 }
 102
 103 #endif /* __LINUX_FILE_H */