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, 2 insertions, 2 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 92ce83a11e90..22cc38d9e79f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -2078,8 +2078,8 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
         fd_install(0, rp);
         spin_lock(&cf->file_lock);
         fdt = files_fdtable(cf);
-        FD_SET(0, fdt->open_fds);
-        FD_CLR(0, fdt->close_on_exec);
+        __set_open_fd(0, fdt);
+        __clear_close_on_exec(0, fdt);
         spin_unlock(&cf->file_lock);
 
         /* and disallow core files too */