git: DragonFly_RELEASE_4_6 vkernel - Add COW image capability

[Matthew Dillon]

commit 9fb6182a431801bf588fe53fcb7ce94a7f8f3553
Author: Matthew Dillon <dillon at backplane.com>
Date:   Sun Oct 9 16:41:17 2016 -0700

    vkernel - Add COW image capability
    
    * Add a copy-on-write disk image feature.  This allows a vkernel
      to mount a disk image RO or R+W but does not try to write changes
      back to the image file.
    
      This allows multiple vkernel instances to use the same image
      file.
    
    * Note that when the vkernel operates on an image in this mode,
      modifications will eat up system memory and swap, so the user
      should be cognizant of the use-case.  Still, the flexiblity of
      being able to mount the image R+W should not be underestimated.

Summary of changes:
 share/man/man7/vkernel.7                | 33 ++++++++++++++++++-
 sys/dev/virtual/vkernel/disk/vdisk.c    | 56 +++++++++++++++++++++++++++------
 sys/platform/vkernel64/include/md_var.h |  2 ++
 sys/platform/vkernel64/platform/init.c  | 44 ++++++++++++++++----------
 4 files changed, 108 insertions(+), 27 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/9fb6182a431801bf588fe53fcb7ce94a7f8f3553


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