[libvirt] [PATCH] Allow saving QEMU libvirt state to a pipe

[Roy Keene]

All,

     Currently the "virsh save" command opens a file to save a domain's 
XML and memory state, does the save, and then re-opens the file to 
simulate seeking to the beginning to update the header to indicate that 
the file is complete.

For pipes this is not possible, attempting to re-open the pipe will not 
connect you to the same consumer.  Seeking is also not possible on a pipe.

Attached is a patch that detects if the file being written to is not 
seekable, and if so writes the completed header initially, then writes 
the normal data, and avoids re-opening the file.

This is useful to me for saving a VM state directly to Ceph RBD images 
without having an intermediate file.

I've tested this patch successfully (against v1.3.5) for both saving and 
restoring a domain:

# *( fifo="$(mktemp -u)"; mkfifo "${fifo}" && virsh save one-0 "${fifo}" 
& cat "${fifo}" | rbd import - rbd/test1234 & wait; rm -f "${fifo}" )*

Domain one-0 saved to /tmp/tmp.HK4hChiQqB

#

# *( fifo="$(mktemp -u)"; mkfifo "${fifo}" && rbd export rbd/test1234 - 
 > "${fifo}" & virsh restore "${fifo}" & wait; rm -f "${fifo}" ) *
Exporting image: 100% complete...done.
Domain restored from /tmp/tmp.0YaUZ5Y2yT

# *virsh list*
  Id    Name                           State
----------------------------------------------------
  11    one-0                          running
#

-- 
	Roy Keene
	Knight Point Systems, LLC
	Service-Disabled Veteran-Owned Business
	1775 Wiehle Avenue Suite 101 | Reston, VA 20190
	c: 813-956-3808    f: 571-266-3106
	www.knightpoint.com
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	GSA Schedule 70 SDVOSB: GS-35F-0646S
	GSA MOBIS Schedule: GS-10F-0404Y
	ISO 20000 / ISO 27001

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