file: Merge __fd_install into fd_install

The function __fd_install was added to support binder[1].  With binder
fixed[2] there are no more users.

As fd_install just calls __fd_install with "files=current->files",
merge them together by transforming the files parameter into a
local variable initialized to current->files.

[1] f869e8a ("expose a low-level variant of fd_install() for binder")
[2] 44d8047 ("binder: use standard functions to allocate fds")
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
v1:https://lkml.kernel.org/r/20200817220425.9389-14-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20201120231441.29911-18-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/file.c

@@ -158,7 +158,7 @@ static int expand_fdtable(struct files_struct *files, unsigned int nr)
 	spin_unlock(&files->file_lock);
 	new_fdt = alloc_fdtable(nr);
 
-	/* make sure all __fd_install() have seen resize_in_progress
+	/* make sure all fd_install() have seen resize_in_progress
 	 * or have finished their rcu_read_lock_sched() section.
 	 */
 	if (atomic_read(&files->count) > 1)
@@ -181,7 +181,7 @@ static int expand_fdtable(struct files_struct *files, unsigned int nr)
 	rcu_assign_pointer(files->fdt, new_fdt);
 	if (cur_fdt != &files->fdtab)
 		call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
-	/* coupled with smp_rmb() in __fd_install() */
+	/* coupled with smp_rmb() in fd_install() */
 	smp_wmb();
 	return 1;
 }
@@ -584,17 +584,13 @@ EXPORT_SYMBOL(put_unused_fd);
  * It should never happen - if we allow dup2() do it, _really_ bad things
  * will follow.
  *
- * NOTE: __fd_install() variant is really, really low-level; don't
- * use it unless you are forced to by truly lousy API shoved down
- * your throat.  'files' *MUST* be either current->files or obtained
- * by get_files_struct(current) done by whoever had given it to you,
- * or really bad things will happen.  Normally you want to use
- * fd_install() instead.
+ * This consumes the "file" refcount, so callers should treat it
+ * as if they had called fput(file).
  */
 
-void __fd_install(struct files_struct *files, unsigned int fd,
-		struct file *file)
+void fd_install(unsigned int fd, struct file *file)
 {
+	struct files_struct *files = current->files;
 	struct fdtable *fdt;
 
 	rcu_read_lock_sched();
@@ -616,15 +612,6 @@ void __fd_install(struct files_struct *files, unsigned int fd,
 	rcu_read_unlock_sched();
 }
 
-/*
- * This consumes the "file" refcount, so callers should treat it
- * as if they had called fput(file).
- */
-void fd_install(unsigned int fd, struct file *file)
-{
-	__fd_install(current->files, fd, file);
-}
-
 EXPORT_SYMBOL(fd_install);
 
 static struct file *pick_file(struct files_struct *files, unsigned fd)

include/linux/fdtable.h

@@ -126,8 +126,6 @@ int iterate_fd(struct files_struct *, unsigned,
 
 extern int __alloc_fd(struct files_struct *files,
 		      unsigned start, unsigned end, unsigned flags);
-extern void __fd_install(struct files_struct *files,
-		      unsigned int fd, struct file *file);
 extern int __close_fd(struct files_struct *files,
 		      unsigned int fd);
 extern int __close_range(unsigned int fd, unsigned int max_fd, unsigned int flags);