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

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

[nishant mungse]

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 ?

Regards,
Nishant.

Re: How to test the read/write flow of dm-target.

[Malahal Naineni]

nishant mungse [nishantmungse@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.

Re: How to test the read/write flow of dm-target.

[nishant mungse]

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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@us.ibm.com> wrote:

> nishant mungse [nishantmungse@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.
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>

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Re: How to test the read/write flow of dm-target.

[Milan Broz]

On 01/30/2011 07:37 PM, nishant mungse wrote:
> Is there any way to find the last sector of bio.

Use csope to study kernel code, there is lot of examples
in existing code.

For last used sector in bio you probably want
last_used_sector = bio->bi_sector + bio_sectors(bio) - 1;

Milan

p.s.
Please do not post repeated questions in different threads
(and spam messages like chat invitations) to list, thank you.