vfs: improve comment describing fget_light()

Improve the description of fget_light(), which is currently incorrect about needing a prior refcnt (judging by the way it is actually used). Signed-off-by: Tony Battersby <tonyb@cybernetics.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

vfs: improve comment describing fget_light()
Improve the description of fget_light(), which is currently incorrect about needing a prior refcnt (judging by the way it is actually used). Signed-off-by: Tony Battersby <tonyb@cybernetics.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Tony Battersby · Linus Torvalds
1 parent 5a19ae4bb0
Showing 1 changed file with 14 additions and 5 deletions Side-by-side Diff
fs/file_table.c
@@ -298,11 +298,20 @@
 EXPORT_SYMBOL(fget);
  
 /*
- * Lightweight file lookup - no refcnt increment if fd table isn't shared. 
- * You can use this only if it is guranteed that the current task already 
- * holds a refcnt to that file. That check has to be done at fget() only
- * and a flag is returned to be passed to the corresponding fput_light().
- * There must not be a cloning between an fget_light/fput_light pair.
+ * 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)
 {
...	...	@@ -298,11 +298,20 @@
298	298	EXPORT_SYMBOL(fget);
299	299
300	300	/*
301		- * Lightweight file lookup - no refcnt increment if fd table isn't shared.
302		- * You can use this only if it is guranteed that the current task already
303		- * holds a refcnt to that file. That check has to be done at fget() only
304		- * and a flag is returned to be passed to the corresponding fput_light().
305		- * There must not be a cloning between an fget_light/fput_light pair.
	301	+ * Lightweight file lookup - no refcnt increment if fd table isn't shared.
	302	+ *
	303	+ * You can use this instead of fget if you satisfy all of the following
	304	+ * conditions:
	305	+ * 1) You must call fput_light before exiting the syscall and returning control
	306	+ * to userspace (i.e. you cannot remember the returned struct file * after
	307	+ * returning to userspace).
	308	+ * 2) You must not call filp_close on the returned struct file * in between
	309	+ * calls to fget_light and fput_light.
	310	+ * 3) You must not clone the current task in between the calls to fget_light
	311	+ * and fput_light.
	312	+ *
	313	+ * The fput_needed flag returned by fget_light should be passed to the
	314	+ * corresponding fput_light.
306	315	*/
307	316	struct file fget_light(unsigned int fd, int fput_needed)
308	317	{