Re: [Xen-devel] [PATCH] [XM-TEST] block device write verify test 2nd attempt

[Harry Butterworth <harry@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

On Wed, 2006-05-24 at 11:20 +0100, Ewan Mellor wrote:
> On Tue, May 23, 2006 at 01:35:35PM +0100, Harry Butterworth wrote:
> 
> > On Tue, 2006-05-23 at 12:40 +0100, Ewan Mellor wrote:
> > > On Tue, May 23, 2006 at 11:35:55AM +0100, Harry Butterworth wrote:
> > > 
> > > > The only difference from the last version of the patch is that the minor
> > > > version number in configure.ac is incremented.
> > > > 
> > > > >From the patch:
> > > > 
> > > > +# This test imports a ram disk device as a physical device into a domU.
> > > > +# The domU initialises the ram disk with data from /dev/urandom and
> > > > calculates
> > > > +# the md5 checksum of the data (using tee as it is written so as to
> > > > avoid
> > > > +# reading it back from the device which might potentially mask
> > > > problems).
> > > > +# The domU is stopped and the md5 checksum of the data on the device is
> > > > +# calculated by dom0.  The test succeeds if the checksums match,
> > > > indicating
> > > > +# that all the data written by domU was sucessfully committed to the
> > > > device.
> > > > +
> > > > 
> > > > This patch also enables tee and fancy head in busybox on the ramdisk.  I
> > > > have tested the patch with both `make existing' where the tests run but
> > > > the new test fails because the ramdisk is missing tee and fancy head and
> > > > `make` where the test passes successfully.
> > > 
> > > Why don't you use dd instead of head -c?
> > 
> > I tried using dd with a block size of 1 and a count of the right number
> > of bytes but the test was very slow.  I didn't want to assume a 512b
> > block size and I'm not very good at shell script so didn't manage to
> > work out how to do it better.
> 
> dd bs=<number> count=1 should do just fine.

The ram disk is 64MB, I thought that this would require a 64MB buffer in
domU which I thought was too big.  It would be better to use dd with the
correct block size and count of blocks.

> 
> > > Why don't you just fix the size of the datablock that you write to the
> > > ramdisk, instead of determining the current size of the ramdisk with cat
> > > /dev/hda1 | wc -c?
> > 
> > I wanted to test writing at the device limits.  Sometimes there are off
> > by one errors that mean you can't write the last sector of a block
> > device.
> > 
> > cat | wc -c was the most robust way I could think of for getting the
> > size.
> 
> How about blockdev --getsize64 /dev/ram1?

blockdev and stat are not available in the ramdisk.  I could use
blockdev to get the blocksize and number of blocks in dom0 and then pass
the values to domU but it would be better to obtain all the information
in domU since that would test whether the size of the device is
correctly passed from the back to the front by the blk driver.

The test as it stands does check that aspect of the blk driver operation
and is only a factor of 2 slower than the limit and the python code is
trivial so I thought it was reasonable.

Can you think of any way to get the block size and number of blocks
using tools available on the ramdisk?

> 
> Ewan.
> 
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> 


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