migration: various dirty page tracking fixes (#457)

- document how to use a vfio-user device with libvirt
- document how to use SPDK's nvmf/vfio-user target with libvirt
- replace vfio_bitmap with vfio_user_bitmap and vfio_iommu_type1_dirty_bitmap_get with vfio_user_bitmap_range
- fix bug for calculating number of pages needed for dirty page bitmap
- align number of bytes for dirty page bitmap to QWORD
- add debug messages around dirty page tracking
- only support flags=0 when doing DMA unmap
- set device state to running after reset
- allow region read/write even if device is in stopped state
- allow transitioning from stopped/stop-and-copy state to running state
- fix unit tests

Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
Reviewed-by: John Levon <john.levon@nutanix.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/README.md b/README.md
index 8b69713..462f85b 100644
--- a/README.md
+++ b/README.md
@@ -194,6 +194,49 @@ the emulated GPIO device's pins:
     cat /sys/class/gpio/gpiochip480/base > /sys/class/gpio/export
     for ((i=0;i<12;i++)); do cat /sys/class/gpio/OUT0/value; done
 
+libvirt
+-------
+
+1. Add `xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'` to the `domain`
+   element.
+
+2. Enable sharing of the guest's RAM:
+
+    <memoryBacking>
+      <source type='file'/>
+      <access mode='shared'/>
+    </memoryBacking>
+
+3. Pass the vfio-user device:
+
+    <qemu:commandline>
+      <qemu:arg value='-device'/>
+      <qemu:arg value='vfio-user-pci,socket=/var/run/vfio-user.sock,x-enable-migration=on'/>
+    </qemu:commandline>
+
+
+nvmf/vfio-user
+--------------
+
+[SPDK v21.01](https://github.com/spdk/spdk/releases/tag/v21.01) added
+experimental support for a virtual NVMe controller. The controller can be
+used with the same command line as the one used for GPIO.
+
+To use the nvmf/vfio-user target with a libvirt quest, the guest RAM must be
+backed by hugepages:
+
+    <memoryBacking>
+      <hugepages>
+        <page size='2048' unit='KiB'/>
+      </hugepages>
+      <source type='memfd'/>
+      <access mode='shared'/>
+    </memoryBacking>
+
+Becasue SPDK must be run as root, either fix the vfio-user socket permissions
+or configure libvirt to run QEMU as root.
+
+
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