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, 4 insertions, 4 deletions

diff --git a/fs/file.c b/fs/file.c
index 4c6992d..114fea0 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -366,7 +366,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 			 * is partway through open().  So make sure that this
 			 * fd is available to the new process.
 			 */
-			FD_CLR(open_files - i, new_fdt->open_fds);
+			__clear_open_fd(open_files - i, new_fdt);
 		}
 		rcu_assign_pointer(*new_fds++, f);
 	}
@@ -460,11 +460,11 @@ repeat:
 	if (start <= files->next_fd)
 		files->next_fd = fd + 1;
 
-	FD_SET(fd, fdt->open_fds);
+	__set_open_fd(fd, fdt);
 	if (flags & O_CLOEXEC)
-		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);
 	error = fd;
 #if 1
 	/* Sanity check */