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

[nishant mungse]

Hi Malahal

Is there any way to find the last sector of bio.
Is this a correct way to find last sector of bio

"bio->bi_sector=bio->bi_sector + (bio->bi_size >> 9)-1"

or

bio_for_each_segment(bvec,bio,
idx)
{
 bio->bi_sector=bio->bi_sector + (bvec->bv_len >> 9) -1;
}
Actually what i think both are same thing but in different way. Will this
bio->bi_sector point to last sector of bio if bio->bi_vcnt is greater than
1.
What is correct way to find/get last sector from bio?
Regards,
Nishant.


On Fri, Jan 28, 2011 at 2:42 PM, Malahal Naineni <malahal at us.ibm.com> wrote:

> 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.
>
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