take fget() and friends to fs/file.c

[karo-tx-linux.git] / fs / file.c

diff --git a/fs/file.c b/fs/file.c
index 0d1bf05151112d1692eaf3681a3ddfed49e05c2f..6eef55ce30c94ae400139a03ac14daf5b4098769 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -625,3 +625,109 @@ void fd_install(unsigned int fd, struct file *file)
 }
 
 EXPORT_SYMBOL(fd_install);
+
+struct file *fget(unsigned int fd)
+{
+       struct file *file;
+       struct files_struct *files = current->files;
+
+       rcu_read_lock();
+       file = fcheck_files(files, fd);
+       if (file) {
+               /* File object ref couldn't be taken */
+               if (file->f_mode & FMODE_PATH ||
+                   !atomic_long_inc_not_zero(&file->f_count))
+                       file = NULL;
+       }
+       rcu_read_unlock();
+
+       return file;
+}
+
+EXPORT_SYMBOL(fget);
+
+struct file *fget_raw(unsigned int fd)
+{
+       struct file *file;
+       struct files_struct *files = current->files;
+
+       rcu_read_lock();
+       file = fcheck_files(files, fd);
+       if (file) {
+               /* File object ref couldn't be taken */
+               if (!atomic_long_inc_not_zero(&file->f_count))
+                       file = NULL;
+       }
+       rcu_read_unlock();
+
+       return file;
+}
+
+EXPORT_SYMBOL(fget_raw);
+
+/*
+ * Lightweight file lookup - no refcnt increment if fd table isn't shared.
+ *
+ * You can use this instead of fget if you satisfy all of the following
+ * conditions:
+ * 1) You must call fput_light before exiting the syscall and returning control
+ *    to userspace (i.e. you cannot remember the returned struct file * after
+ *    returning to userspace).
+ * 2) You must not call filp_close on the returned struct file * in between
+ *    calls to fget_light and fput_light.
+ * 3) You must not clone the current task in between the calls to fget_light
+ *    and fput_light.
+ *
+ * The fput_needed flag returned by fget_light should be passed to the
+ * corresponding fput_light.
+ */
+struct file *fget_light(unsigned int fd, int *fput_needed)
+{
+       struct file *file;
+       struct files_struct *files = current->files;
+
+       *fput_needed = 0;
+       if (atomic_read(&files->count) == 1) {
+               file = fcheck_files(files, fd);
+               if (file && (file->f_mode & FMODE_PATH))
+                       file = NULL;
+       } else {
+               rcu_read_lock();
+               file = fcheck_files(files, fd);
+               if (file) {
+                       if (!(file->f_mode & FMODE_PATH) &&
+                           atomic_long_inc_not_zero(&file->f_count))
+                               *fput_needed = 1;
+                       else
+                               /* Didn't get the reference, someone's freed */
+                               file = NULL;
+               }
+               rcu_read_unlock();
+       }
+
+       return file;
+}
+
+struct file *fget_raw_light(unsigned int fd, int *fput_needed)
+{
+       struct file *file;
+       struct files_struct *files = current->files;
+
+       *fput_needed = 0;
+       if (atomic_read(&files->count) == 1) {
+               file = fcheck_files(files, fd);
+       } else {
+               rcu_read_lock();
+               file = fcheck_files(files, fd);
+               if (file) {
+                       if (atomic_long_inc_not_zero(&file->f_count))
+                               *fput_needed = 1;
+                       else
+                               /* Didn't get the reference, someone's freed */
+                               file = NULL;
+               }
+               rcu_read_unlock();
+       }
+
+       return file;
+}