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[Xen-devel] printk calls in xen-blkback/blkback.c not appearing

  • To: xen-devel <xen-devel@xxxxxxxxxxxxx>
  • From: Misiu Godfrey <misiu.godfrey@xxxxxxxxx>
  • Date: Tue, 29 Jan 2013 11:39:07 -0500
  • Delivery-date: Tue, 29 Jan 2013 16:42:01 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>

Hello Xen community,

I am having some trouble debugging code in blkback.c.  Specifically, I
can't get any printk() statements within this file to show up (which
makes me think the code is not being executed).  Originally, I just
had them in dispatch_rw_block_io() (where the submit_bio call is) but
I have been experimenting with other functions and can't get them to
work anywhere.  I can verify that my domUs are writing to disk, so
they must be using some i/o interface and, as far as I am aware,
blkback.c:dispatch_rw_block_io():submit_bio() should be the bottleneck

I am running a dom0 with Ubuntu 12.04 with kernel version 3.2.28 and
two domUs with sparse Ubuntu installs. The DomU's are reading and
writing to the disk without issue, except that they seem to be doing
it through different channels than the ones I am tracing.

Does anyone have any suggestions why these statements might not be
showing up (I have bumped them up to KERN_EMERG to make sure it's not
a loglevel thing), or not executing?  Is there a good way to verify
that the proper xen-blkback module is being used, or not?  Have I
correctly determined that blkback.c should be the bottleneck for all
domU i/o?

Any comments are appreciated,

With thanks,


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