Re: [linux-usb-devel] Re: USB storage problems on OHCI..

[James Bottomley <James.Bottomley@steeleye.com>]

On Tue, 2003-09-23 at 10:23, Alan Stern wrote: 
> Is there any way to notify the system that you are about to unplug a 
> drive?  It seems to me that the best approach is to flush the cache on an 
> unmount.  People naturally assume that it's safe to unplug a device once 
> it has been unmounted, and they also realize that it's unsafe to unplug a 
> device containing a mounted filesystem.
> 
> That doesn't address the problem of raw device access, but perhaps 
> whatever ioctl is used by blockdev --flushbufs can also flush the cache.

Well, a synchronize can be really expensive (minutes to flush on a large
array), you only really want to do it if absolutely necessary, so tying
it to something separate from normal OS operation seems like the best
thing to do. 

> Is there any harm in sending a SYNCHRONIZE command to a device that
> doesn't need it (write-through cache)?  Maybe doing that is less dangerous 
> than trying to read mode-sense page 8 on these buggy USB devices.  
> (Although I'm not aware of anyone who has tried the experiment.)

Devices that don't support mode page 8 invariably seem to react badly to
the SYNCHRONIZE command (I have a few of these SCSI devices)...Although,
usually they just send an ILLEGAL COMMAND sense.  I wouldn't like to try
the same thing with a USB device... 

James