On Tue, 21 Feb 2023 at 23:10, Jonathon Jongsma <jjongsma@redhat.com> wrote:

On 2/17/23 10:50 AM, Christian Nautze wrote:
> Currently it's only possible to set this parameter during domain
> creation via QEMU commandline passthrough feature.
> With the new delay attribute it's also possible to set this
> parameter if you want to attach a new NBD disk
> using "virsh attach-device domain device.xml" e.g.:
>
> <disk type='network' device='disk'>
> <driver name='qemu' type='raw'/>
> <source protocol='nbd' name='foo'>
> <host name='example.org' port='6000'/>
> <reconnect delay='10'/>
> </source>
> <target dev='vdb' bus='virtio'/>
> </disk>
>
> Signed-off-by: Christian Nautze <christian.nautze@exoscale.ch>
>

I wonder about the choice between using an attribute vs a child element
for this value. Most of the things that use child elements for are more
complex values. For example, 'host' is an address and a port, 'cookies'
is a collection of cookie elements, even the existing 'reconnect'
element has two sub-values. On the other hand, things that are a simple
value tend to be specified as attributes instead. NBD sources in
particular have attributes 'name', 'tls', and 'tlsHostname'. Since this
is a single integer value, I wonder if it would make more sense to use
another nbd-specific attribute such as 'reconnectDelay'. For example:

<source protocol='nbd' name='foo' reconnectDelay='10'>

This might also reduce potential confusion about how to specify the
'reconnect' element, but has the downside of having two different
reconnect-related elements. To be honest, I'm not sure whether there is
an overal philosophy on attributes vs. elements, so I will happily defer
to more veteran libvirt developers.

If we do use the <reconnect> sub-element, I think the schema would need
to use <choice> to indicate that it's either ('enabled'+'timeout') OR
'delay', not an arbitrary subset of these attributes.

Jonathon

> ---
> Change: reconnect element: drop mandatory 'enabled' attribute when using 'delay'
> ---
> docs/formatdomain.rst | 11 +++++++--
> src/conf/domain_conf.c | 12 ++++++++++
> src/conf/schemas/domaincommon.rng | 3 +++
> src/conf/schemas/storagecommon.rng | 13 ++++++++---
> src/conf/storage_source_conf.c | 1 +
> src/conf/storage_source_conf.h | 4 ++++
> src/qemu/qemu_block.c | 4 +++-
> src/qemu/qemu_domain.c | 9 ++++++++
> .../disk-network-nbd.x86_64-latest.args | 23 +++++++++++--------
> tests/qemuxml2argvdata/disk-network-nbd.xml | 8 +++++++
> tests/qemuxml2xmloutdata/disk-network-nbd.xml | 9 ++++++++
> 11 files changed, 81 insertions(+), 16 deletions(-)
>
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index 36c6d87907..ee30c51cea 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -2946,13 +2946,20 @@ paravirtualized driver is specified via the ``disk`` element.
> are intended to be default, then the entire element may be omitted.
> ``reconnect``
> For disk type ``vhostuser`` configures reconnect timeout if the connection
> - is lost. It has two mandatory attributes:
> + is lost. This is set with the two mandatory attributes ``enabled`` and
> + ``timeout``.
> + For disk type ``network`` and protocol ``nbd`` the QEMU NBD reconnect delay
> + can be set via attribute ``delay``:
>
> ``enabled``
> If the reconnect feature is enabled, accepts ``yes`` and ``no``
> ``timeout``
> The amount of seconds after which hypervisor tries to reconnect.
> -
> + ``delay``
> + Only for NBD hosts. The amount of seconds during which all requests are
> + paused and will be rerun after a successful reconnect. After that time, any
> + delayed requests and all future requests before a successful reconnect
> + will immediately fail. If not set the default QEMU value is 0.
>
> For a "file" or "volume" disk type which represents a cdrom or floppy (the
> ``device`` attribute), it is possible to define policy what to do with the
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index a5578324b9..3f2ba2aab8 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -7146,6 +7146,15 @@ virDomainDiskSourceNetworkParse(xmlNodePtr node,
> src->tlsFromConfig = !!value;
> }
>
> + if (src->protocol == VIR_STORAGE_NET_PROTOCOL_NBD) {
> + xmlNodePtr cur;
> + if ((cur = virXPathNode("./reconnect", ctxt))) {
> + if (virXMLPropUInt(cur, "delay", 10, VIR_XML_PROP_NONE,
> + &src->reconnectDelay) < 0)
> + return -1;
> + }
> + }
> +
> /* for historical reasons we store the volume and image name in one XML
> * element although it complicates thing when attempting to access them. */
> if (src->path &&
> @@ -22073,6 +22082,9 @@ virDomainDiskSourceFormatNetwork(virBuffer *attrBuf,
> virBufferAddLit(childBuf, "/>\n");
> }
>
> + if (src->reconnectDelay) {
> + virBufferAsprintf(childBuf, "<reconnect delay='%u'/>\n", src->reconnectDelay);
> + }
>
> virBufferEscapeString(childBuf, "<snapshot name='%s'/>\n", src->snapshot);
> virBufferEscapeString(childBuf, "<config file='%s'/>\n", src->configFile);
> diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
> index a57dd212ab..dd5fbeac09 100644
> --- a/src/conf/schemas/domaincommon.rng
> +++ b/src/conf/schemas/domaincommon.rng
> @@ -2199,6 +2199,9 @@
> </optional>
> <ref name="diskSourceCommon"/>
> <ref name="diskSourceNetworkHost"/>
> + <optional>
> + <ref name="reconnect"/>
> + </optional>
> <optional>
> <ref name="encryption"/>
> </optional>
> diff --git a/src/conf/schemas/storagecommon.rng b/src/conf/schemas/storagecommon.rng
> index 4d6e646c9a..582375358c 100644
> --- a/src/conf/schemas/storagecommon.rng
> +++ b/src/conf/schemas/storagecommon.rng
> @@ -55,14 +55,21 @@
>
> <define name="reconnect">
> <element name="reconnect">
> - <attribute name="enabled">
> - <ref name="virYesNo"/>
> - </attribute>
> + <optional>
> + <attribute name="enabled">
> + <ref name="virYesNo"/>
> + </attribute>
> + </optional>
> <optional>
> <attribute name="timeout">
> <ref name="unsignedInt"/>
> </attribute>
> </optional>
> + <optional>
> + <attribute name="delay">
> + <ref name="unsignedInt"/>
> + </attribute>
> + </optional>
> </element>
> </define>
>
> diff --git a/src/conf/storage_source_conf.c b/src/conf/storage_source_conf.c
> index cecd7e811e..58009fd06e 100644
> --- a/src/conf/storage_source_conf.c
> +++ b/src/conf/storage_source_conf.c
> @@ -811,6 +811,7 @@ virStorageSourceCopy(const virStorageSource *src,
> def->sslverify = src->sslverify;
> def->readahead = src->readahead;
> def->timeout = src->timeout;
> + def->reconnectDelay = src->reconnectDelay;
> def->metadataCacheMaxSize = src->metadataCacheMaxSize;
>
> /* storage driver metadata are not copied */
> diff --git a/src/conf/storage_source_conf.h b/src/conf/storage_source_conf.h
> index 14a6825d54..c6187dda59 100644
> --- a/src/conf/storage_source_conf.h
> +++ b/src/conf/storage_source_conf.h
> @@ -312,6 +312,10 @@ struct _virStorageSource {
> unsigned long long readahead; /* size of the readahead buffer in bytes */
> unsigned long long timeout; /* connection timeout in seconds */
>
> + /* NBD QEMU reconnect-delay option,
> + * 0 as default value */
> + unsigned int reconnectDelay;
> +
> virStorageSourceNVMeDef *nvme; /* type == VIR_STORAGE_TYPE_NVME */
>
> virDomainChrSourceDef *vhostuser; /* type == VIR_STORAGE_TYPE_VHOST_USER */
> diff --git a/src/qemu/qemu_block.c b/src/qemu/qemu_block.c
> index 5e700eff99..8fcebd8992 100644
> --- a/src/qemu/qemu_block.c
> +++ b/src/qemu/qemu_block.c
> @@ -529,6 +529,7 @@ qemuBlockStorageSourceGetNBDProps(virStorageSource *src,
> "S:export", src->path,
> "S:tls-creds", tlsAlias,
> "S:tls-hostname", tlsHostname,
> + "p:reconnect-delay", src->reconnectDelay,
> NULL) < 0)
> return NULL;
>
> @@ -1848,7 +1849,8 @@ qemuBlockGetBackingStoreString(virStorageSource *src,
> src->ncookies == 0 &&
> src->sslverify == VIR_TRISTATE_BOOL_ABSENT &&
> src->timeout == 0 &&
> - src->readahead == 0) {
> + src->readahead == 0 &&
> + src->reconnectDelay == 0) {
>
> switch ((virStorageNetProtocol) src->protocol) {
> case VIR_STORAGE_NET_PROTOCOL_NBD:
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index e9bc0f375d..02ae3823fb 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -5020,6 +5020,15 @@ qemuDomainValidateStorageSource(virStorageSource *src,
> }
> }
>
> + if (src->reconnectDelay > 0) {
> + if (actualType != VIR_STORAGE_TYPE_NETWORK ||
> + src->protocol != VIR_STORAGE_NET_PROTOCOL_NBD) {
> + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> + _("reconnect delay is supported only with NBD protocol"));
> + return -1;
> + }
> + }
> +
> if (src->query &&
> (actualType != VIR_STORAGE_TYPE_NETWORK ||
> (src->protocol != VIR_STORAGE_NET_PROTOCOL_HTTPS &&
> diff --git a/tests/qemuxml2argvdata/disk-network-nbd.x86_64-latest.args b/tests/qemuxml2argvdata/disk-network-nbd.x86_64-latest.args
> index 21e619af3e..e8d13b0bd4 100644
> --- a/tests/qemuxml2argvdata/disk-network-nbd.x86_64-latest.args
> +++ b/tests/qemuxml2argvdata/disk-network-nbd.x86_64-latest.args
> @@ -28,21 +28,24 @@ XDG_CONFIG_HOME=/tmp/lib/domain--1-QEMUGuest1/.config \
> -no-acpi \
> -boot strict=on \
> -device '{"driver":"piix3-usb-uhci","id":"usb","bus":"pci.0","addr":"0x1.0x2"}' \
> --blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"node-name":"libvirt-5-storage","auto-read-only":true,"discard":"unmap"}' \
> +-blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"node-name":"libvirt-6-storage","auto-read-only":true,"discard":"unmap"}' \
> +-blockdev '{"node-name":"libvirt-6-format","read-only":false,"driver":"raw","file":"libvirt-6-storage"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x2","drive":"libvirt-6-format","id":"virtio-disk0","bootindex":1}' \
> +-blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"export":"bar","node-name":"libvirt-5-storage","auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-5-format","read-only":false,"driver":"raw","file":"libvirt-5-storage"}' \
> --device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x2","drive":"libvirt-5-format","id":"virtio-disk0","bootindex":1}' \
> --blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"export":"bar","node-name":"libvirt-4-storage","auto-read-only":true,"discard":"unmap"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x3","drive":"libvirt-5-format","id":"virtio-disk1"}' \
> +-blockdev '{"driver":"nbd","server":{"type":"inet","host":"::1","port":"6000"},"node-name":"libvirt-4-storage","auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-4-format","read-only":false,"driver":"raw","file":"libvirt-4-storage"}' \
> --device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x3","drive":"libvirt-4-format","id":"virtio-disk1"}' \
> --blockdev '{"driver":"nbd","server":{"type":"inet","host":"::1","port":"6000"},"node-name":"libvirt-3-storage","auto-read-only":true,"discard":"unmap"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x4","drive":"libvirt-4-format","id":"virtio-disk2"}' \
> +-blockdev '{"driver":"nbd","server":{"type":"inet","host":"::1","port":"6000"},"export":"bar","node-name":"libvirt-3-storage","auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-3-format","read-only":false,"driver":"raw","file":"libvirt-3-storage"}' \
> --device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x4","drive":"libvirt-3-format","id":"virtio-disk2"}' \
> --blockdev '{"driver":"nbd","server":{"type":"inet","host":"::1","port":"6000"},"export":"bar","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x5","drive":"libvirt-3-format","id":"virtio-disk3"}' \
> +-blockdev '{"driver":"nbd","server":{"type":"unix","path":"/var/run/nbdsock"},"export":"bar","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-2-format","read-only":false,"driver":"raw","file":"libvirt-2-storage"}' \
> --device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x5","drive":"libvirt-2-format","id":"virtio-disk3"}' \
> --blockdev '{"driver":"nbd","server":{"type":"unix","path":"/var/run/nbdsock"},"export":"bar","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x6","drive":"libvirt-2-format","id":"virtio-disk4"}' \
> +-blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"export":"foo","reconnect-delay":10,"node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-1-format","read-only":false,"driver":"raw","file":"libvirt-1-storage"}' \
> --device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x6","drive":"libvirt-1-format","id":"virtio-disk4"}' \
> +-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x7","drive":"libvirt-1-format","id":"virtio-disk5"}' \
> -audiodev '{"id":"audio1","driver":"none"}' \
> -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
> -msg timestamp=on
> diff --git a/tests/qemuxml2argvdata/disk-network-nbd.xml b/tests/qemuxml2argvdata/disk-network-nbd.xml
> index 8ac6cc3b7b..4e8b1e5b03 100644
> --- a/tests/qemuxml2argvdata/disk-network-nbd.xml
> +++ b/tests/qemuxml2argvdata/disk-network-nbd.xml
> @@ -49,6 +49,14 @@
> </source>
> <target dev='vde' bus='virtio'/>
> </disk>
> + <disk type='network' device='disk'>
> + <driver name='qemu' type='raw'/>
> + <source protocol='nbd' name='foo'>
> + <host name='example.org' port='6000'/>
> + <reconnect delay='10'/>
> + </source>
> + <target dev='vdf' bus='virtio'/>
> + </disk>
> <controller type='usb' index='0'/>
> <controller type='ide' index='0'/>
> <controller type='pci' index='0' model='pci-root'/>
> diff --git a/tests/qemuxml2xmloutdata/disk-network-nbd.xml b/tests/qemuxml2xmloutdata/disk-network-nbd.xml
> index f8dcca4bab..38d1f290c8 100644
> --- a/tests/qemuxml2xmloutdata/disk-network-nbd.xml
> +++ b/tests/qemuxml2xmloutdata/disk-network-nbd.xml
> @@ -54,6 +54,15 @@
> <target dev='vde' bus='virtio'/>
> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
> </disk>
> + <disk type='network' device='disk'>
> + <driver name='qemu' type='raw'/>
> + <source protocol='nbd' name='foo'>
> + <host name='example.org' port='6000'/>
> + <reconnect delay='10'/>
> + </source>
> + <target dev='vdf' bus='virtio'/>
> + <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
> + </disk>
> <controller type='usb' index='0'>
> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
> </controller>