Re: Too verbose compat_ioctl messages?

Geert Uytterhoeven wrote:

Fuse-san discovered that running the umount that's part of busybox on a PS3
with a recent kernel causes an error message to be printed on the console:

| ioctl32(busybox:1340): Unknown cmd fd(3) cmd(00004c01){t:'L';sz:0} arg(00000000) on /dev/sda1 

On older kernels (e.g. 2.6.16), this doesn't happen.

It can easily be reproduced by installing busybox and running

| busybox umount /mountpoint

on a mounted filesystem (except when using the loop device).

Apparently Busybox uses the LOOP_CLR_FD ioctl when unmounting a file system,
which is supported by the loop device only.
On other block device types, this ioctl is not supported:
  - With a 64-bit application, the block layer returns ENOTTY (Inappropriate
    ioctl for device), while the SCSI layer returns EINVAL (Invalid argument)
  - With a 32-bit application, the compat_ioctl code returns EINVAL (Invalid
    argument) and prints an error on the console (for the first 50
    occurrencies, cfr. fs/compat_ioctl.c:compat_sys_ioctl())

As I understand, compat_ioctl_error() is used to inform the user about ioctl
values that are not yet handled by the compat_ioctl layer. However, LOOP_CLR_FD
doesn't need to be handled (no data to convert between 32-bit and 64-bit), and
it's perfectly valid for a block device to not implement it.
So it's confusing to print this error message.

Is there anything we can do about this?

For one thing, it looks like we're returning the wrong thing (EINVAL
rather than ENOTTY) across the board.  This was unfortunately a common
misunderstanding with non-tty-related ioctls in the early days of Linux.

	-hpa