Re: HDIO_DRIVE_CMD and hdparm

[Christoph Hellwig <hch@infradead.org>]

On Thu, May 10, 2007 at 02:12:59PM +0200, Geert Uytterhoeven wrote:
> 	Hi,
> 
> `hdparm -t' uses HDIO_DRIVE_CMD(null) to flush the disk's buffer.
> When using it on my own block device (the new PS3 disk storage driver), hdparm
> gives the following error message:
> 
> | HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device
> 
> When using it on an ATA or SCSI device, no such error message is printed.
> 
> According to the hdparm sources, hdparm expects the HDIO_DRIVE_CMD(null) ioctl
> to either succeed, or to fail with errno EINVAL.
> 
> Apparently handling of ioctls is different for the different device types:
>   - ATA/SATA handle HDIO_DRIVE_CMD(null) (and a few other variants)
>     => fine for hdparm
>   - SCSI doesn't handle HDIO_DRIVE_CMD(null), and returns EINVAL
>     => fine for hdparm
>   - If a block device doesn't support the ioctl, blkdev_driver_ioctl() returns
>     ENOTTY
>     => hdparm error message
> 
> Which one is correct?
>   - blkdev_ioctl()/blkdev_driver_ioctl() return -ENOTTY
>   - scsi_cmd_ioctl() returns -ENOTTY
>   - scsi_ioctl() returns -EINVAL
>   - cdrom_ioctl() returns -ENOSYS to mean not handled, continue
>   - some block layer routines return -ENOIOCTLCMD to mean not handled, continue

ENOTTY is the traditional unix errno value for this ioctl is not implemented.
ENOIOCTLCMD is a new fashioned code meaning about the same.  In the block
layer the latter should be used as generic code should handlde this.

> 
> My questions:
>   1. Does any of these have to be fixed?
>   2. Shall I add a dummy HDIO_DRIVE_CMD(null) handler to my block device to
>      return -EINVAL?
>   3. Shall I just ignore the hdparm error message?

I suspect you can just ignore this.  Even better send a patch to the hdparm
maintainer to deal with ENOTTY aswell.