new helper: iterate_fd()

iterates through the opened files in given descriptor table,
calling a supplied function; we stop once non-zero is returned.
Callback gets struct file *, descriptor number and const void *
argument passed to iterator.  It is called with files->file_lock
held, so it is not allowed to block.

tty_io, netprio_cgroup and selinux flush_unauthorized_files()
converted to its use.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/file.c b/fs/file.c
index 967bd0dadbe5..e6e418122587 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -979,3 +979,24 @@ int f_dupfd(unsigned int from, struct file *file, unsigned flags)
         }
         return err;
 }
+
+int iterate_fd(struct files_struct *files, unsigned n,
+                int (*f)(const void *, struct file *, unsigned),
+                const void *p)
+{
+        struct fdtable *fdt;
+        struct file *file;
+        int res = 0;
+        if (!files)
+                return 0;
+        spin_lock(&files->file_lock);
+        fdt = files_fdtable(files);
+        while (!res && n < fdt->max_fds) {
+                file = rcu_dereference_check_fdtable(files, fdt->fd[n++]);
+                if (file)
+                        res = f(p, file, n);
+        }
+        spin_unlock(&files->file_lock);
+        return res;
+}
+EXPORT_SYMBOL(iterate_fd);