I'm not sure what the problem is here, but a couple of things
would help me to diagnose it further.

(0) Try virt-v2v 1.27.38 -- which hopefully I'll be uploading
later today.

(1) In virt-v2v 1.27.38 it should be possible to import directly
from the remote Xen hypervisor, ie:

  virt-v2v -ic xen+ssh://root@xen [...]

Read the section in the virt-v2v manual about "INPUT FROM RHEL 5 XEN"
first however.

(2) If it's still failing, can you add the -v -x options and
then give the complete output.  It will be very large, so
redirect it into a file like this:

  virt-v2v -v -x [.....] |& tee /tmp/log

(In reply to Richard W.M. Jones from comment #2)
> I'm not sure what the problem is here, but a couple of things
> would help me to diagnose it further.
> 
> (0) Try virt-v2v 1.27.38 -- which hopefully I'll be uploading
> later today.

I tried the below version,kernal panic again.
virt-v2v-1.27.39-1.1.el7.x86_64
libguestfs-1.27.39-1.1.el7.x86_64
libguestfs-tools-c-1.27.39-1.1.el7.x86_64

> (1) In virt-v2v 1.27.38 it should be possible to import directly
> from the remote Xen hypervisor, ie:
> 
>   virt-v2v -ic xen+ssh://root@xen [...]
> 
> Read the section in the virt-v2v manual about "INPUT FROM RHEL 5 XEN"
> first however.

Tried to use -ic xen+ssh://root@xen [...]
# sshkey-gen
# ssh-copy-id -i /root/.ssh/id_rsa.pub root@$xenserver
# eval `ssh-agent`
# ssh-add
# virt-v2v -v -x -ic xen+ssh://10.66.106.64 -os default --network default rhel6.6-pv-x64-test |& tee /tmp/v2v-xen.log

Conversion is successful,but guest still fails to boot,attach the log file for reference.

Created attachment 935557 [details]
Log file of converting xen guest

Created attachment 935572 [details]
Log file of converting xen guest -new

Pls ignore comment 4,I've uploaded the new log file.

The bug seems to be caused because we call dracut with the wrong
kernel version parameter.  Dracut itself prints an error:

/sbin/dracut --add-drivers "virtio virtio_ring virtio_blk virtio_net virtio_pci" \
  /boot/initramfs-2.6.32-496.el6.x86_64.img 2.6.32-496.el6
find: `/lib/modules/2.6.32-496.el6/': No such file or directory
find: `/lib/modules/2.6.32-496.el6/': No such file or directory
find: `/lib/modules/2.6.32-496.el6/': No such file or directory
find: `/lib/modules/2.6.32-496.el6/': No such file or directory
find: `/lib/modules/2.6.32-496.el6/': No such file or directory
find: `/lib/modules/2.6.32-496.el6/': No such file or directory

but doesn't actually exit with a detectable status code, and
therefore we continue, but the initramfs of the guest has been
destroyed, and hence the VM won't boot.

I was able to reproduce this problem easily simply by running virt-v2v
on a RHEL 6.5 guest image -- no Xen is needed.

The incorrect dracut parameter is fixed in this commit:

https://github.com/libguestfs/libguestfs/commit/59136518f13cb489cc17a411267d54444d7c8ac6

Unfortunately the second problem of dracut not exiting with
a useful status code is harder to fix.  What happens is that
it creates a corrupted initramfs (if it created nothing at
all, we could at least detect that).  Of course even fixing
dracut won't help since we cannot go back in time to fix
old guests with broken dracut/mkinitrd.

I can reproduce this issue as bug description.

And try to verify it with new version:
virt-v2v-1.27.41-1.1.el7.x86_64
libguestfs-1.27.41-1.1.el7.x86_64

Tried to use -ic xen+ssh://root@xen [...]
# sshkey-gen
# ssh-copy-id -i /root/.ssh/id_rsa.pub root@$xenserver
# eval `ssh-agent`
# ssh-add
# virt-v2v -v -x -ic xen+ssh://10.66.106.64 -os default --network default rhel6.6-pv-x64-test 

Result: Conversion is successful, and guest successfully to boot up.
Move to VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-0303.html