[dm-devel] How to test the read/write flow of dm-target.

[Malahal Naineni]

nishant mungse [nishantmungse at gmail.com] wrote:
> Hi,
> 
> I've created a device mapper target and I wanna test its read and
> write mechanisms. I created a device using this target and tried to
> write a filesystem on to the device.
> 
> My target is creating roughly two outgoing bios per incoming bio.
> Which is maybe why I'm not able to get a proper log after running the
> mke2fs command as while writing the filesystem, there are massive
> amounts of writes performed on the device.
> 
> So, I tried to use the cat command to directly write to the device
> file. The write is being performed for sure because I'm able to view
> the data written to the underlying device.
> 
> But there is no output when I try to read the device file contents using cat.
> 
> Is there any other way to test the read/write workflows of a dm target
> that can give out a proper log ?

I am not sure what you mean by 'proper log'. I would use 'dd' with
direct I/O to avoid cache so that every read and write directly go to the
device. I don't think you can do that with 'cat' command.