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Subject[PATCH] compat_ioctl: introduce generic_compat_ioctl helper
Many drivers use only compatible ioctl numbers. In order to
avoid having to write a special compat_ioctl handler for each
of them or listing every ioctl number in fs/compat_ioctl.c,
let's introduce a generic handler that simply calls the
driver specific f_op->unlocked_ioctl() or f_op->ioctl() handler.

Signed-off-by: Arnd Bergman <>
On Saturday 13 October 2007, Al Viro wrote:
> Just how many instances of that sucker do we need? It's nothing but
> struct inode *inode = file->f_path.dentry->d_inode;
> return file->f_op->ioctl(inode, file, cmd, compat_ptr(arg));

Is this what you had in mind? I've been meaning to do something like
it for some time, but had forgotten about it.

I guess we can kill a significant amount of COMPATIBLE_IOCTL
lines in fs/compat_ioctl.c with this.

Index: linux-2.6/fs/compat_ioctl.c
--- linux-2.6.orig/fs/compat_ioctl.c
+++ linux-2.6/fs/compat_ioctl.c
@@ -1877,6 +1877,30 @@ lp_timeout_trans(unsigned int fd, unsign
return sys_ioctl(fd, cmd, (unsigned long)tn);

+ * Helper function for device drivers that only have COMPATIBLE_IOCTL
+ * numbers. This can be used as f_op->compat_ioctl without any #ifdef
+ * and will simply call the native ioctl handler with the argument
+ * pointer.
+ * Don't use for drivers that interpret arg as an unsigned long instead
+ * of a pointer.
+ */
+long generic_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+ int ret = -ENOTTY;
+ arg = (unsigned long)compat_ptr(arg);
+ if (file->f_op->unlocked_ioctl)
+ ret = file->f_op->unlocked_ioctl(file, cmd, arg);
+ else if (file->f_op->ioctl) {
+ lock_kernel();
+ ret = file->f_op->ioctl(file->f_dentry->d_inode, file, cmd, arg);
+ unlock_kernel();
+ }
+ return ret;

typedef int (*ioctl_trans_handler_t)(unsigned int, unsigned int,
unsigned long, struct file *);
Index: linux-2.6/include/linux/fs.h
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -1807,6 +1807,12 @@ extern void do_generic_mapping_read(stru
extern int generic_segment_checks(const struct iovec *iov,
unsigned long *nr_segs, size_t *count, int access_flags);

+extern long generic_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+#define generic_compat_ioctl (long (*)(struct file *, unsigned int, unsigned long))NULL
/* fs/splice.c */
extern ssize_t generic_file_splice_read(struct file *, loff_t *,
struct pipe_inode_info *, size_t, unsigned int);
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