Replace the fd_sets in struct fdtable with an array of unsigned longs

Replace the fd_sets in struct fdtable with an array of unsigned longs and then
use the standard non-atomic bit operations rather than the FD_* macros.

This:

(1) Removes the abuses of struct fd_set:

(a) Since we don't want to allocate a full fd_set the vast majority of the
time, we actually, in effect, just allocate a just-big-enough array of
unsigned longs and cast it to an fd_set type - so why bother with the
fd_set at all?

(b) Some places outside of the core fdtable handling code (such as
SELinux) want to look inside the array of unsigned longs hidden inside
the fd_set struct for more efficient iteration over the entire set.

(2) Eliminates the use of FD_*() macros in the kernel completely.

(3) Permits the __FD_*() macros to be deleted entirely where not exposed to
userspace.

Signed-off-by: David Howells <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: H. Peter Anvin <[e-mail]>
Cc: Al Viro <[e-mail]>

fs/exec.c

···
 		fdt = files_fdtable(files);
 		if (i >= fdt->max_fds)
 			break;
-		set = fdt->close_on_exec->fds_bits[j];
+		set = fdt->close_on_exec[j];
 		if (!set)
 			continue;
-		fdt->close_on_exec->fds_bits[j] = 0;
+		fdt->close_on_exec[j] = 0;
 		spin_unlock(&files->file_lock);
 		for ( ; set ; i++,set >>= 1) {
 			if (set & 1) {

fs/file.c

···
  */
 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
 
-static void *alloc_fdmem(unsigned int size)
+static void *alloc_fdmem(size_t size)
 {
 	/*
 	 * Very large allocations can stress page reclaim, so fall back to
···
 static struct fdtable * alloc_fdtable(unsigned int nr)
 {
 	struct fdtable *fdt;
-	char *data;
+	void *data;
 
 	/*
 	 * Figure out how many fds we actually want to support in this fdtable.
···
 	data = alloc_fdmem(nr * sizeof(struct file *));
 	if (!data)
 		goto out_fdt;
-	fdt->fd = (struct file **)data;
-	data = alloc_fdmem(max_t(unsigned int,
+	fdt->fd = data;
+
+	data = alloc_fdmem(max_t(size_t,
 				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 	if (!data)
 		goto out_arr;
-	fdt->open_fds = (fd_set *)data;
-	data += nr / BITS_PER_BYTE;
-	fdt->close_on_exec = (fd_set *)data;
+	fdt->open_fds = data;
+	data += nr / BITS_PER_LONG;
+	fdt->close_on_exec = data;
 	fdt->next = NULL;
 
 	return fdt;
···
 	int i;
 
 	/* Find the last open fd */
-	for (i = size/(8*sizeof(long)); i > 0; ) {
-		if (fdt->open_fds->fds_bits[--i])
+	for (i = size / BITS_PER_LONG; i > 0; ) {
+		if (fdt->open_fds[--i])
 			break;
 	}
-	i = (i+1) * 8 * sizeof(long);
+	i = (i + 1) * BITS_PER_LONG;
 	return i;
 }
 
···
 	newf->next_fd = 0;
 	new_fdt = &newf->fdtab;
 	new_fdt->max_fds = NR_OPEN_DEFAULT;
-	new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
-	new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
+	new_fdt->close_on_exec = newf->close_on_exec_init;
+	new_fdt->open_fds = newf->open_fds_init;
 	new_fdt->fd = &newf->fd_array[0];
 	new_fdt->next = NULL;
 
···
 	old_fds = old_fdt->fd;
 	new_fds = new_fdt->fd;
 
-	memcpy(new_fdt->open_fds->fds_bits,
-		old_fdt->open_fds->fds_bits, open_files/8);
-	memcpy(new_fdt->close_on_exec->fds_bits,
-		old_fdt->close_on_exec->fds_bits, open_files/8);
+	memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
+	memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
 
 	for (i = open_files; i != 0; i--) {
 		struct file *f = *old_fds++;
···
 	memset(new_fds, 0, size);
 
 	if (new_fdt->max_fds > open_files) {
-		int left = (new_fdt->max_fds-open_files)/8;
-		int start = open_files / (8 * sizeof(unsigned long));
+		int left = (new_fdt->max_fds - open_files) / 8;
+		int start = open_files / BITS_PER_LONG;
 
-		memset(&new_fdt->open_fds->fds_bits[start], 0, left);
-		memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
+		memset(&new_fdt->open_fds[start], 0, left);
+		memset(&new_fdt->close_on_exec[start], 0, left);
 	}
 
 	rcu_assign_pointer(newf->fdt, new_fdt);
···
 	.fdtab		= {
 		.max_fds	= NR_OPEN_DEFAULT,
 		.fd		= &init_files.fd_array[0],
-		.close_on_exec	= (fd_set *)&init_files.close_on_exec_init,
-		.open_fds	= (fd_set *)&init_files.open_fds_init,
+		.close_on_exec	= init_files.close_on_exec_init,
+		.open_fds	= init_files.open_fds_init,
 	},
 	.file_lock	= __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 };
···
 		fd = files->next_fd;
 
 	if (fd < fdt->max_fds)
-		fd = find_next_zero_bit(fdt->open_fds->fds_bits,
-					   fdt->max_fds, fd);
+		fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
 
 	error = expand_files(files, fd);
 	if (error < 0)

fs/select.c

···
 	set = ~(~0UL << (n & (__NFDBITS-1)));
 	n /= __NFDBITS;
 	fdt = files_fdtable(current->files);
-	open_fds = fdt->open_fds->fds_bits+n;
+	open_fds = fdt->open_fds + n;
 	max = 0;
 	if (set) {
 		set &= BITS(fds, n);

include/linux/fdtable.h

···
  */
 #define NR_OPEN_DEFAULT BITS_PER_LONG
 
-/*
- * The embedded_fd_set is a small fd_set,
- * suitable for most tasks (which open <= BITS_PER_LONG files)
- */
-struct embedded_fd_set {
-	unsigned long fds_bits[1];
-};
-
 struct fdtable {
 	unsigned int max_fds;
 	struct file __rcu **fd;      /* current fd array */
-	fd_set *close_on_exec;
-	fd_set *open_fds;
+	unsigned long *close_on_exec;
+	unsigned long *open_fds;
 	struct rcu_head rcu;
 	struct fdtable *next;
 };
 
 static inline void __set_close_on_exec(int fd, struct fdtable *fdt)
 {
-	FD_SET(fd, fdt->close_on_exec);
+	__set_bit(fd, fdt->close_on_exec);
 }
 
 static inline void __clear_close_on_exec(int fd, struct fdtable *fdt)
 {
-	FD_CLR(fd, fdt->close_on_exec);
+	__clear_bit(fd, fdt->close_on_exec);
 }
 
 static inline bool close_on_exec(int fd, const struct fdtable *fdt)
 {
-	return FD_ISSET(fd, fdt->close_on_exec);
+	return test_bit(fd, fdt->close_on_exec);
 }
 
 static inline void __set_open_fd(int fd, struct fdtable *fdt)
 {
-	FD_SET(fd, fdt->open_fds);
+	__set_bit(fd, fdt->open_fds);
 }
 
 static inline void __clear_open_fd(int fd, struct fdtable *fdt)
 {
-	FD_CLR(fd, fdt->open_fds);
+	__clear_bit(fd, fdt->open_fds);
 }
 
 static inline bool fd_is_open(int fd, const struct fdtable *fdt)
 {
-	return FD_ISSET(fd, fdt->open_fds);
+	return test_bit(fd, fdt->open_fds);
 }
 
 /*
···
    */
 	spinlock_t file_lock ____cacheline_aligned_in_smp;
 	int next_fd;
-	struct embedded_fd_set close_on_exec_init;
-	struct embedded_fd_set open_fds_init;
+	unsigned long close_on_exec_init[1];
+	unsigned long open_fds_init[1];
 	struct file __rcu * fd_array[NR_OPEN_DEFAULT];
 };
 

kernel/exit.c

···
 		i = j * __NFDBITS;
 		if (i >= fdt->max_fds)
 			break;
-		set = fdt->open_fds->fds_bits[j++];
+		set = fdt->open_fds[j++];
 		while (set) {
 			if (set & 1) {
 				struct file * file = xchg(&fdt->fd[i], NULL);

security/selinux/hooks.c

···
 		fdt = files_fdtable(files);
 		if (i >= fdt->max_fds)
 			break;
-		set = fdt->open_fds->fds_bits[j];
+		set = fdt->open_fds[j];
 		if (!set)
 			continue;
 		spin_unlock(&files->file_lock);