Wrap accesses to the fd_sets in struct fdtable

Wrap accesses to the fd_sets in struct fdtable (for recording open files and
close-on-exec flags) so that we can move away from using fd_sets since we
abuse the fd_set structs by not allocating the full-sized structure under
normal circumstances and by non-core code looking at the internals of the
fd_sets.

The first abuse means that use of FD_ZERO() on these fd_sets is not permitted,
since that cannot be told about their abnormal lengths.

This introduces six wrapper functions for setting, clearing and testing
close-on-exec flags and fd-is-open flags:

	void __set_close_on_exec(int fd, struct fdtable *fdt);
	void __clear_close_on_exec(int fd, struct fdtable *fdt);
	bool close_on_exec(int fd, const struct fdtable *fdt);
	void __set_open_fd(int fd, struct fdtable *fdt);
	void __clear_open_fd(int fd, struct fdtable *fdt);
	bool fd_is_open(int fd, const struct fdtable *fdt);

Note that I've prepended '__' to the names of the set/clear functions because
they require the caller to hold a lock to use them.

Note also that I haven't added wrappers for looking behind the scenes at the
the array.  Possibly that should exist too.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: http://lkml.kernel.org/r/20120216174942.23314.1364.stgit@warthog.procyon.org.uk
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 9 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 22764c7c838..75e7c1f3a08 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -32,20 +32,20 @@ void set_close_on_exec(unsigned int fd, int flag)
         spin_lock(&files->file_lock);
         fdt = files_fdtable(files);
         if (flag)
-                FD_SET(fd, fdt->close_on_exec);
+                __set_close_on_exec(fd, fdt);
         else
-                FD_CLR(fd, fdt->close_on_exec);
+                __clear_close_on_exec(fd, fdt);
         spin_unlock(&files->file_lock);
 }
 
-static int get_close_on_exec(unsigned int fd)
+static bool get_close_on_exec(unsigned int fd)
 {
         struct files_struct *files = current->files;
         struct fdtable *fdt;
-        int res;
+        bool res;
         rcu_read_lock();
         fdt = files_fdtable(files);
-        res = FD_ISSET(fd, fdt->close_on_exec);
+        res = close_on_exec(fd, fdt);
         rcu_read_unlock();
         return res;
 }
@@ -90,15 +90,15 @@ SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
         err = -EBUSY;
         fdt = files_fdtable(files);
         tofree = fdt->fd[newfd];
-        if (!tofree && FD_ISSET(newfd, fdt->open_fds))
+        if (!tofree && fd_is_open(newfd, fdt))
                 goto out_unlock;
         get_file(file);
         rcu_assign_pointer(fdt->fd[newfd], file);
-        FD_SET(newfd, fdt->open_fds);
+        __set_open_fd(newfd, fdt);
         if (flags & O_CLOEXEC)
-                FD_SET(newfd, fdt->close_on_exec);
+                __set_close_on_exec(newfd, fdt);
         else
-                FD_CLR(newfd, fdt->close_on_exec);
+                __clear_close_on_exec(newfd, fdt);
         spin_unlock(&files->file_lock);
 
         if (tofree)