On 12/2/19 9:26 AM, Michal Privoznik wrote:
There is this class of PCI devices that act like disks: NVMe. Therefore, they are both PCI devices and disks. While we already have <hostdev/> (and can assign a NVMe device to a domain successfully) we don't have disk representation. There are three problems with PCI assignment in case of a NVMe device:
1) domains with <hostdev/> can't be migrated
2) NVMe device is assigned whole, there's no way to assign only a namespace
3) Because hypervisors see <hostdev/> they don't put block layer on top of it - users don't get all the fancy features like snapshots
NVMe namespaces are way of splitting one continuous NVDIMM memory into smaller ones, effectively creating smaller NVMe-s (which can then be partitioned, LVMed, etc.)
Because of all of this the following XML was chosen to model a NVMe device:
<disk type='nvme' device='disk'> <driver name='qemu' type='raw'/> <source type='pci' managed='yes' namespace='1'> <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> </source> <target dev='vda' bus='virtio'/> </disk>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- docs/formatdomain.html.in | 57 +++++++++++++++++++++++-- docs/schemas/domaincommon.rng | 32 ++++++++++++++ tests/qemuxml2argvdata/disk-nvme.xml | 63 ++++++++++++++++++++++++++++ 3 files changed, 149 insertions(+), 3 deletions(-) create mode 100644 tests/qemuxml2argvdata/disk-nvme.xml
diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in index 6df4a8b26e..fe871d933f 100644 --- a/docs/formatdomain.html.in +++ b/docs/formatdomain.html.in @@ -2944,6 +2944,13 @@ </backingStore> <target dev='vdd' bus='virtio'/> </disk> + <disk type='nvme' device='disk'> + <driver name='qemu' type='raw'/> + <source type='pci' managed='yes' namespace='1'> + <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/> + </source> + <target dev='vde' bus='virtio'/> + </disk> </devices> ...</pre>
@@ -2957,7 +2964,8 @@ Valid values are "file", "block", "dir" (<span class="since">since 0.7.5</span>), "network" (<span class="since">since 0.8.7</span>), or - "volume" (<span class="since">since 1.0.5</span>) + "volume" (<span class="since">since 1.0.5</span>), or + "nvme" (<span class="since">since 5.6.0</span>)
6.0.0 or whatever version this will land in
and refer to the underlying source for the disk. <span class="since">Since 0.0.3</span> </dd> @@ -3140,6 +3148,43 @@ <span class="since">Since 1.0.5</span> </p> </dd> + <dt><code>nvme</code></dt> + <dd> + To specify disk source for NVMe disk the <code>source</code> + element has the following attributes: + <dl> + <dt><code>type</code></dt> + <dd>The type of address specified in <code>address</code> + sub-element. Currently, only <code>pci</code> value is + accepted. + </dd> + + <dt><code>managed</code></dt> + <dd>This attribute instructs libvirt to detach NVMe + controller automatically on domain startup (<code>yes</code>) + or expect the controller to be detached by system + administrator (<code>no</code>). + </dd> + + <dt><code>namespace</code></dt> + <dd>The namespace ID which should be assigned to the domain. + According to NVMe standard, namespace numbers start from 1, + including. + </dd> + </dl> + + The difference between <code><disk type='nvme'></code> + and <code><hostdev/></code> is that the latter is plain + host device assignment with all its limitations (e.g. no live + migration), while the former makes hypervisor to run the NVMe + disk through hypervisor's block layer thus enabling all + features provided by the layer (e.g. snapshots, domain + migration, etc.). Moreover, since the NVMe disk is unbinded + from its PCI driver, the host kernel storage stack is not + involved (compared to passing say <code>/dev/nvme0n1</code> via + <code><disk type='block'></code> and therefore lower + latencies can be achieved. + </dd> </dl> With "file", "block", and "volume", one or more optional sub-elements <code>seclabel</code>, <a href="#seclabel">described @@ -3302,11 +3347,17 @@ initiator IQN needed to access the source via mandatory attribute <code>name</code>. </dd> + <dt><code>address</code></dt> + <dd>For disk of type <code>nvme</code> this element + specifies the PCI address of the host NVMe + controller. + <span class="since">Since 5.6.0</span>
Same
+ </dd> </dl>
<p> - For a "file" or "volume" disk type which represents a cdrom or floppy - (the <code>device</code> attribute), it is possible to define + For a "file" or "volume" disk type which represents a cdrom or + floppy (the <code>device</code> attribute), it is possible to define
Stray change? Also, tn the test XML you need to "s/qemu-system-i686/qemu-system-i386/" or you'll hit a weird error. And VIR_TEST_REGENERATE_OUTPUT is also busted, see my patches elsewhere on this list. Reviewed-by: Cole Robinson <crobinso@redhat.com> - Cole