[PATCH] merge locate_fd() and get_unused_fd()

New primitive: alloc_fd(start, flags). get_unused_fd() and
get_unused_fd_flags() become wrappers on top of it.

Signed-off-by: Al Viro <[e-mail]>

fs/fcntl.c

···
 	return res;
 }
 
-/*
- * locate_fd finds a free file descriptor in the open_fds fdset,
- * expanding the fd arrays if necessary.  Must be called with the
- * file_lock held for write.
- */
-
-static int locate_fd(unsigned int orig_start, int cloexec)
-{
-	struct files_struct *files = current->files;
-	unsigned int newfd;
-	unsigned int start;
-	int error;
-	struct fdtable *fdt;
-
-	spin_lock(&files->file_lock);
-repeat:
-	fdt = files_fdtable(files);
-	/*
-	 * Someone might have closed fd's in the range
-	 * orig_start..fdt->next_fd
-	 */
-	start = orig_start;
-	if (start < files->next_fd)
-		start = files->next_fd;
-
-	newfd = start;
-	if (start < fdt->max_fds)
-		newfd = find_next_zero_bit(fdt->open_fds->fds_bits,
-					   fdt->max_fds, start);
-
-	error = expand_files(files, newfd);
-	if (error < 0)
-		goto out;
-
-	/*
-	 * If we needed to expand the fs array we
-	 * might have blocked - try again.
-	 */
-	if (error)
-		goto repeat;
-
-	if (start <= files->next_fd)
-		files->next_fd = newfd + 1;
-
-	FD_SET(newfd, fdt->open_fds);
-	if (cloexec)
-		FD_SET(newfd, fdt->close_on_exec);
-	else
-		FD_CLR(newfd, fdt->close_on_exec);
-	error = newfd;
-
-out:
-	spin_unlock(&files->file_lock);
-	return error;
-}
-
-static int dupfd(struct file *file, unsigned int start, int cloexec)
-{
-	int fd = locate_fd(start, cloexec);
-	if (fd >= 0)
-		fd_install(fd, file);
-	else
-		fput(file);
-
-	return fd;
-}
-
 asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
 	int err = -EBADF;
···
 asmlinkage long sys_dup(unsigned int fildes)
 {
 	int ret = -EBADF;
-	struct file * file = fget(fildes);
+	struct file *file = fget(fildes);
 
-	if (file)
-		ret = dupfd(file, 0, 0);
+	if (file) {
+		ret = get_unused_fd();
+		if (ret >= 0)
+			fd_install(ret, file);
+		else
+			fput(file);
+	}
 	return ret;
 }
 
···
 	case F_DUPFD_CLOEXEC:
 		if (arg >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
 			break;
-		get_file(filp);
-		err = dupfd(filp, arg, cmd == F_DUPFD_CLOEXEC);
+		err = alloc_fd(arg, cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0);
+		if (err >= 0) {
+			get_file(filp);
+			fd_install(err, filp);
+		}
 		break;
 	case F_GETFD:
 		err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;

fs/file.c

···
  *  Manage the dynamic fd arrays in the process files_struct.
  */
 
+#include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/time.h>
···
 	},
 	.file_lock	= __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 };
+
+/*
+ * allocate a file descriptor, mark it busy.
+ */
+int alloc_fd(unsigned start, unsigned flags)
+{
+	struct files_struct *files = current->files;
+	unsigned int fd;
+	int error;
+	struct fdtable *fdt;
+
+	spin_lock(&files->file_lock);
+repeat:
+	fdt = files_fdtable(files);
+	fd = start;
+	if (fd < files->next_fd)
+		fd = files->next_fd;
+
+	if (fd < fdt->max_fds)
+		fd = find_next_zero_bit(fdt->open_fds->fds_bits,
+					   fdt->max_fds, fd);
+
+	error = expand_files(files, fd);
+	if (error < 0)
+		goto out;
+
+	/*
+	 * If we needed to expand the fs array we
+	 * might have blocked - try again.
+	 */
+	if (error)
+		goto repeat;
+
+	if (start <= files->next_fd)
+		files->next_fd = fd + 1;
+
+	FD_SET(fd, fdt->open_fds);
+	if (flags & O_CLOEXEC)
+		FD_SET(fd, fdt->close_on_exec);
+	else
+		FD_CLR(fd, fdt->close_on_exec);
+	error = fd;
+#if 1
+	/* Sanity check */
+	if (rcu_dereference(fdt->fd[fd]) != NULL) {
+		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
+		rcu_assign_pointer(fdt->fd[fd], NULL);
+	}
+#endif
+
+out:
+	spin_unlock(&files->file_lock);
+	return error;
+}
+
+int get_unused_fd(void)
+{
+	return alloc_fd(0, 0);
+}
+EXPORT_SYMBOL(get_unused_fd);

fs/open.c

···
 }
 EXPORT_SYMBOL(dentry_open);
 
-/*
- * Find an empty file descriptor entry, and mark it busy.
- */
-int get_unused_fd_flags(int flags)
-{
-	struct files_struct * files = current->files;
-	int fd, error;
-	struct fdtable *fdt;
-
-	spin_lock(&files->file_lock);
-
-repeat:
-	fdt = files_fdtable(files);
-	fd = find_next_zero_bit(fdt->open_fds->fds_bits, fdt->max_fds,
-				files->next_fd);
-
-	/* Do we need to expand the fd array or fd set?  */
-	error = expand_files(files, fd);
-	if (error < 0)
-		goto out;
-
-	if (error) {
-		/*
-	 	 * If we needed to expand the fs array we
-		 * might have blocked - try again.
-		 */
-		goto repeat;
-	}
-
-	FD_SET(fd, fdt->open_fds);
-	if (flags & O_CLOEXEC)
-		FD_SET(fd, fdt->close_on_exec);
-	else
-		FD_CLR(fd, fdt->close_on_exec);
-	files->next_fd = fd + 1;
-#if 1
-	/* Sanity check */
-	if (fdt->fd[fd] != NULL) {
-		printk(KERN_WARNING "get_unused_fd: slot %d not NULL!\n", fd);
-		fdt->fd[fd] = NULL;
-	}
-#endif
-	error = fd;
-
-out:
-	spin_unlock(&files->file_lock);
-	return error;
-}
-
-int get_unused_fd(void)
-{
-	return get_unused_fd_flags(0);
-}
-
-EXPORT_SYMBOL(get_unused_fd);
-
 static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 {
 	struct fdtable *fdt = files_fdtable(files);

include/linux/file.h

···
 extern struct file *fget_light(unsigned int fd, int *fput_needed);
 extern void set_close_on_exec(unsigned int fd, int flag);
 extern void put_filp(struct file *);
+extern int alloc_fd(unsigned start, unsigned flags);
 extern int get_unused_fd(void);
-extern int get_unused_fd_flags(int flags);
+#define get_unused_fd_flags(flags) alloc_fd(0, (flags))
 extern void put_unused_fd(unsigned int fd);
 
 extern void fd_install(unsigned int fd, struct file *file);