RE: Accessing ram drive as raw disk volume fails?

["Dave Korn" <dave dot korn at artimi dot com>]

On 30 November 2006 19:56, Igor Peshansky wrote:

> On Thu, 30 Nov 2006, Dave Korn wrote:
> 
>>     Hi all,
>> 
>>   I'm trying to use dd to dump stuff to a usb flash drive (i.e. mass
>> storage device).  However something tricks it into thinking the device
>> is full (/dev/sdb is the pendrive):
>> 
>> dk@CHILLI ~
>> $ dd if=/tmp/msd-test-data.cXoEqa2332 of=/dev/sdb bs=100 count=1
>> dd: writing `/dev/sdb': No space left on device
>> 1+0 records in
>> 0+0 records out
>> 
>> dk@CHILLI ~
>> $

> strace or gdb should be helpful in identifying the Windows error code that
> is mapped by Cygwin to ENOSPC.  From a quick look at the code, this could
> be a general write error, but I haven't spent all that much time looking
> at it.

  It was.  The strace showed:

   91   15071 [main] dd 3468 fhandler_base::read: returning 100, binary mode
   29   15100 [main] dd 3468 readv: 100 = readv (0, 0x22EE30, 1), errno 0
   31   15131 [main] dd 3468 writev: writev (1, 0x22EE20, 1)
   29   15160 [main] dd 3468 fhandler_base::write: binary write
   53   15213 [main] dd 3468 fhandler_dev_raw::write_file: 0 (err 87) =
WriteFile (1756, 268607488, write 100, written 0, 0)
   34   15247 [main] dd 3468 fhandler_dev_floppy::is_eom: end of medium

which is "ERROR_INVALID_PARAMETER 87 The parameter is incorrect."

  Looking at a comment in fhandler_dev_floppy::ioctl, it looks to me like the
issue is that writes to a raw block device have to be integer multiples of the
blocksize:

    case RDSETBLK:
      /* Just check the restriction that blocksize must be a multiple
	 of the sector size of the underlying volume sector size,
	 then fall through to fhandler_dev_raw::ioctl. */

which I imagine I'll find documented even in MSDN somewhere if I look hard
enough.  So, the answers are:

>> Is this expected behaviour under cygwin?  

  Yes, as indeed under windows in general.

>> What does "no space left on
>> device" even mean for a raw disk volume as opposed to a logical volume /
>> partition?

  It means 'invalid parameter' in this particular instance. 


    cheers,
      DaveK
-- 
Can't think of a witty .sigline today....


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