HDIO_DRIVE_CMD and hdparm

HDIO_DRIVE_CMD and hdparm

[Geert Uytterhoeven]

	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

This causes constructs with different tests like e.g.:

	sr_block_ioctl()
	{
		...
		ret = cdrom_ioctl(...);
		if (ret != -ENOSYS)
			return ret;
		...
		return scsi_ioctl(...);
	}

	cdrom_ioctl()
	{
		...
		ret = scsi_cmd_ioctl(...);
		if (ret != -ENOTTY)
			return ret;
		...
		return -ENOSYS;
	}

	blkdev_ioctl()
	{
		...
		ret = blkdev_locked_ioctl(...);
		...
		if (ret != -ENOIOCTLCMD)
			return ret;

		return blkdev_driver_ioctl(...);
	}

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?

Thanks!

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- Sony Network and Software Technology Center Europe (NSCE)
Geert.Uytterhoeven@sonycom.com ------- The Corporate Village, Da Vincilaan 7-D1
Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium

Re: HDIO_DRIVE_CMD and hdparm

[Christoph Hellwig]

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.

Re: HDIO_DRIVE_CMD and hdparm

[Alan Cox]

>   - 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

Those are both correct
	-ENOTTY 		I don't know this ioctl
	-EINVAL			I know this ioctl, usage wrong
	0			Hey it worked

	ENOIOCTLCMD		Internal (not user exposed)
				for fallthrough

	ENOSYS			CD-ROM being weird.

Re: HDIO_DRIVE_CMD and hdparm

[Mark Lord]

Alan Cox wrote:
>>   - 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
> 
> Those are both correct
> 	-ENOTTY 		I don't know this ioctl
> 	-EINVAL			I know this ioctl, usage wrong

Exactly.
I'll have hdparm-7.4 not complain on ENOTTY as well.

-ml

Re: HDIO_DRIVE_CMD and hdparm

[Mark Lord]

Geert Uytterhoeven wrote:
> 	Hi,
> 
> `hdparm -t' uses HDIO_DRIVE_CMD(null) to flush the disk's buffer.

More correctly, that command is supposed to act like an I/O queue "barrier"
operation, not returning from the syscall until everything queued in front
of it has been issued/completed.

I believe that only the original IDE driver actually implements it, though.
And hdparm-7.4 (not released yet) will no longer complain about ENOTTY.

Note that current versions of hdparm use SG_IO/ATA_16 (SAT) for nearly everything
now, only falling back to the older ioctl's for drivers which reject the SAT attempt.

I'd love to find a USB drive enclosure that supports SAT.
Anyone know of one?

And does the USB storage layer actually pass the ATA_16 packets to the device?

Cheers