[PATCH v3 2/3] Add discard_no_unref option for qcow2 images
Peter Krempa
pkrempa at redhat.com
Fri Jun 23 12:39:23 UTC 2023
From: Jean-Louis Dupond <jean-louis at dupond.be>
Qemu 8.1.0 will add discard_no_unref option for qcow2 images.
When this option is enabled (default=false), then it will no longer
unreference clusters when guest does a discard, but it will just free
the blocks (useful for incremental backups for example) and pass the
discard to the lower layer.
This was implemented to avoid fragmentation within the qcow2 image.
Signed-off-by: Jean-Louis Dupond <jean-louis at dupond.be>
Reviewed-by: Peter Krempa <pkrempa at redhat.com>
Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
docs/formatdomain.rst | 7 ++++
src/conf/domain_conf.c | 8 ++++
src/conf/domain_conf.h | 1 +
src/conf/domain_validate.c | 14 +++++++
src/conf/schemas/domaincommon.rng | 5 +++
src/conf/storage_source_conf.c | 1 +
src/conf/storage_source_conf.h | 1 +
src/qemu/qemu_block.c | 11 +++--
src/qemu/qemu_domain.c | 1 +
src/qemu/qemu_driver.c | 4 +-
src/qemu/qemu_validate.c | 7 ++++
src/vz/vz_utils.c | 6 +++
.../disk-discard_no_unref.x86_64-latest.args | 36 ++++++++++++++++
.../disk-discard_no_unref.xml | 32 ++++++++++++++
tests/qemuxml2argvtest.c | 1 +
.../disk-discard_no_unref.x86_64-latest.xml | 42 +++++++++++++++++++
tests/qemuxml2xmltest.c | 1 +
17 files changed, 171 insertions(+), 7 deletions(-)
create mode 100644 tests/qemuxml2argvdata/disk-discard_no_unref.x86_64-latest.args
create mode 100644 tests/qemuxml2argvdata/disk-discard_no_unref.xml
create mode 100644 tests/qemuxml2xmloutdata/disk-discard_no_unref.x86_64-latest.xml
diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index c3526439bf..2ea440e1a1 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -3284,6 +3284,13 @@ paravirtualized driver is specified via the ``disk`` element.
format driver of the ``qemu`` hypervisor can be controlled via the
``max_size`` subelement (see example below).
+ The optional ``discard_no_unref`` attribute can be set to control the way
+ the ``qemu`` hypervisor handles guest discard commands inside the qcow2
+ image. When enabled, a discard request from within the guest will mark the
+ qcow2 cluster as zero, but will keep the reference/offset of that cluster.
+ But it will still pass the discard further to the lower layer.
+ This will resolve fragmentation within the qcow2 image. :since:`Since 9.5.0`
+
In the majority of cases the default configuration used by the hypervisor
is sufficient so modifying this setting should not be necessary. For
specifics on how the metadata cache of ``qcow2`` in ``qemu`` behaves refer
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 0edb1bda9d..f28cb64eb5 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -7826,6 +7826,10 @@ virDomainDiskDefDriverParseXML(virDomainDiskDef *def,
if (virXMLPropUInt(cur, "queue_size", 10, VIR_XML_PROP_NONE, &def->queue_size) < 0)
return -1;
+ if (virXMLPropTristateSwitch(cur, "discard_no_unref", VIR_XML_PROP_NONE,
+ &def->discard_no_unref) < 0)
+ return -1;
+
return 0;
}
@@ -22501,6 +22505,10 @@ virDomainDiskDefFormatDriver(virBuffer *buf,
virBufferAsprintf(&attrBuf, " detect_zeroes='%s'",
virDomainDiskDetectZeroesTypeToString(disk->detect_zeroes));
+ if (disk->discard_no_unref)
+ virBufferAsprintf(&attrBuf, " discard_no_unref='%s'",
+ virTristateSwitchTypeToString(disk->discard_no_unref));
+
if (disk->queues)
virBufferAsprintf(&attrBuf, " queues='%u'", disk->queues);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 629e32c39f..cddaa3824d 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -606,6 +606,7 @@ struct _virDomainDiskDef {
virDomainDiskDiscard discard;
unsigned int iothread; /* unused = 0, > 0 specific thread # */
virDomainDiskDetectZeroes detect_zeroes;
+ virTristateSwitch discard_no_unref;
char *domain_name; /* backend domain name */
unsigned int queues;
unsigned int queue_size;
diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c
index 7e3c920a38..6c4cfa16d6 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -921,6 +921,20 @@ virDomainDiskDefValidate(const virDomainDef *def,
return -1;
}
+ if (disk->discard_no_unref == VIR_TRISTATE_SWITCH_ON) {
+ if (disk->src->format != VIR_STORAGE_FILE_QCOW2) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("'discard_no_unref' only works with qcow2 disk format"));
+ return -1;
+ }
+
+ if (disk->src->readonly) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("'discard_no_unref' is not compatible with read-only disk"));
+ return -1;
+ }
+ }
+
return 0;
}
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index c1725bb511..87822adcf7 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -2514,6 +2514,11 @@
<optional>
<ref name="detect_zeroes"/>
</optional>
+ <optional>
+ <attribute name="discard_no_unref">
+ <ref name="virOnOff"/>
+ </attribute>
+ </optional>
<optional>
<attribute name="queues">
<ref name="positiveInteger"/>
diff --git a/src/conf/storage_source_conf.c b/src/conf/storage_source_conf.c
index 99061e4df7..dcac3a8ff6 100644
--- a/src/conf/storage_source_conf.c
+++ b/src/conf/storage_source_conf.c
@@ -809,6 +809,7 @@ virStorageSourceCopy(const virStorageSource *src,
def->cachemode = src->cachemode;
def->discard = src->discard;
def->detect_zeroes = src->detect_zeroes;
+ def->discard_no_unref = src->discard_no_unref;
def->sslverify = src->sslverify;
def->readahead = src->readahead;
def->timeout = src->timeout;
diff --git a/src/conf/storage_source_conf.h b/src/conf/storage_source_conf.h
index c6187dda59..f13e7c756a 100644
--- a/src/conf/storage_source_conf.h
+++ b/src/conf/storage_source_conf.h
@@ -399,6 +399,7 @@ struct _virStorageSource {
int cachemode; /* enum virDomainDiskCache */
int discard; /* enum virDomainDiskDiscard */
int detect_zeroes; /* enum virDomainDiskDetectZeroes */
+ virTristateSwitch discard_no_unref;
bool floppyimg; /* set to true if the storage source is going to be used
as a source for floppy drive */
diff --git a/src/qemu/qemu_block.c b/src/qemu/qemu_block.c
index 8b2159f845..dcdf883926 100644
--- a/src/qemu/qemu_block.c
+++ b/src/qemu/qemu_block.c
@@ -1117,12 +1117,11 @@ qemuBlockStorageSourceGetFormatQcow2Props(virStorageSource *src,
* see: qemu.git/docs/qcow2-cache.txt
* https://git.qemu.org/?p=qemu.git;a=blob;f=docs/qcow2-cache.txt
*/
- if (src->metadataCacheMaxSize > 0) {
- if (virJSONValueObjectAdd(&props,
- "U:cache-size", src->metadataCacheMaxSize,
- NULL) < 0)
- return -1;
- }
+ if (virJSONValueObjectAdd(&props,
+ "P:cache-size", src->metadataCacheMaxSize,
+ "T:discard-no-unref", src->discard_no_unref,
+ NULL) < 0)
+ return -1;
return 0;
}
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 8f77e8fc58..a22dac9884 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -11022,6 +11022,7 @@ qemuDomainPrepareDiskSourceData(virDomainDiskDef *disk,
src->iomode = disk->iomode;
src->cachemode = disk->cachemode;
src->discard = disk->discard;
+ src->discard_no_unref = disk->discard_no_unref;
if (disk->device == VIR_DOMAIN_DISK_DEVICE_FLOPPY)
src->floppyimg = true;
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index c4bd766531..f20544590d 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14242,8 +14242,10 @@ qemuDomainBlockCopyCommon(virDomainObj *vm,
* into the topmost virStorage source of the disk chain.
* Since 'mirror' has the ambition to replace it we need to propagate
* it into the mirror too. We do it directly as otherwise we'd need
- * to modify all callers of 'qemuDomainPrepareStorageSourceBlockdev' */
+ * to modify all callers of 'qemuDomainPrepareStorageSourceBlockdev'
+ * Same for discard_no_unref */
mirror->detect_zeroes = disk->detect_zeroes;
+ mirror->discard_no_unref = disk->discard_no_unref;
/* If reusing an external image that includes a backing file but the user
* did not enumerate the chain in the XML we need to detect the chain */
diff --git a/src/qemu/qemu_validate.c b/src/qemu/qemu_validate.c
index 04d0c9df73..a53729d349 100644
--- a/src/qemu/qemu_validate.c
+++ b/src/qemu/qemu_validate.c
@@ -3266,6 +3266,13 @@ qemuValidateDomainDeviceDefDisk(const virDomainDiskDef *disk,
return -1;
}
+ if (disk->discard_no_unref != VIR_TRISTATE_SWITCH_ABSENT &&
+ !virQEMUCapsGet(qemuCaps, QEMU_CAPS_QCOW2_DISCARD_NO_UNREF)) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("'discard_no_unref' is not supported by this QEMU binary"));
+ return -1;
+ }
+
for (n = disk->src; virStorageSourceIsBacking(n); n = n->backingStore) {
if (qemuDomainValidateStorageSource(n, qemuCaps) < 0)
return -1;
diff --git a/src/vz/vz_utils.c b/src/vz/vz_utils.c
index 2db1146149..7db7dbd419 100644
--- a/src/vz/vz_utils.c
+++ b/src/vz/vz_utils.c
@@ -347,6 +347,12 @@ vzCheckDiskUnsupportedParams(virDomainDiskDef *disk)
return -1;
}
+ if (disk->discard_no_unref) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("Disk discard_no_unref is not supported by vz driver."));
+ return -1;
+ }
+
if (disk->startupPolicy != VIR_DOMAIN_STARTUP_POLICY_DEFAULT) {
virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
_("Setting up disk startup policy is not "
diff --git a/tests/qemuxml2argvdata/disk-discard_no_unref.x86_64-latest.args b/tests/qemuxml2argvdata/disk-discard_no_unref.x86_64-latest.args
new file mode 100644
index 0000000000..b9e2939335
--- /dev/null
+++ b/tests/qemuxml2argvdata/disk-discard_no_unref.x86_64-latest.args
@@ -0,0 +1,36 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/var/lib/libvirt/qemu/domain--1-test \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/var/lib/libvirt/qemu/domain--1-test/.local/share \
+XDG_CACHE_HOME=/var/lib/libvirt/qemu/domain--1-test/.cache \
+XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain--1-test/.config \
+/usr/bin/qemu-system-x86_64 \
+-name guest=test,debug-threads=on \
+-S \
+-object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/var/lib/libvirt/qemu/domain--1-test/master-key.aes"}' \
+-machine pc,usb=off,dump-guest-core=off,memory-backend=pc.ram,acpi=off \
+-accel tcg \
+-cpu qemu64 \
+-m 1024 \
+-object '{"qom-type":"memory-backend-ram","id":"pc.ram","size":1073741824}' \
+-overcommit mem-lock=off \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid 92d7a226-cfae-425b-a6d3-00bbf9ec5c9e \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server=on,wait=off \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-boot menu=on,strict=on \
+-device '{"driver":"piix3-usb-uhci","id":"usb","bus":"pci.0","addr":"0x1.0x2"}' \
+-blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/f14.img","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}' \
+-blockdev '{"node-name":"libvirt-1-format","read-only":false,"discard":"unmap","driver":"qcow2","discard-no-unref":true,"file":"libvirt-1-storage"}' \
+-device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x4","drive":"libvirt-1-format","id":"virtio-disk0","bootindex":2}' \
+-audiodev '{"id":"audio1","driver":"none"}' \
+-device '{"driver":"virtio-balloon-pci","id":"balloon0","bus":"pci.0","addr":"0x2"}' \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
+-msg timestamp=on
diff --git a/tests/qemuxml2argvdata/disk-discard_no_unref.xml b/tests/qemuxml2argvdata/disk-discard_no_unref.xml
new file mode 100644
index 0000000000..d5dd054a85
--- /dev/null
+++ b/tests/qemuxml2argvdata/disk-discard_no_unref.xml
@@ -0,0 +1,32 @@
+<domain type='qemu'>
+ <name>test</name>
+ <uuid>92d7a226-cfae-425b-a6d3-00bbf9ec5c9e</uuid>
+ <memory unit='KiB'>1048576</memory>
+ <currentMemory unit='KiB'>1048576</currentMemory>
+ <vcpu placement='static'>1</vcpu>
+ <os>
+ <type arch='x86_64' machine='pc'>hvm</type>
+ <boot dev='cdrom'/>
+ <boot dev='hd'/>
+ <bootmenu enable='yes'/>
+ </os>
+ <clock offset='utc'/>
+ <on_poweroff>destroy</on_poweroff>
+ <on_reboot>restart</on_reboot>
+ <on_crash>restart</on_crash>
+ <devices>
+ <emulator>/usr/bin/qemu-system-x86_64</emulator>
+ <!-- For this disk, intentionally stress parser resilience to
+ atypical ordering -->
+ <disk device='disk'>
+ <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
+ <source file='/var/lib/libvirt/images/f14.img'/>
+ <target dev='vda' bus='virtio'/>
+ <driver discard='unmap' discard_no_unref='on' name='qemu' type='qcow2'/>
+ </disk>
+ <controller type='usb' index='0'/>
+ <controller type='ide' index='0'/>
+ <controller type='pci' index='0' model='pci-root'/>
+ <memballoon model='virtio'/>
+ </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index d914d8cbea..2dda9c4501 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -1245,6 +1245,7 @@ mymain(void)
DO_TEST_CAPS_LATEST("disk-copy_on_read");
DO_TEST_CAPS_LATEST("disk-discard");
DO_TEST_CAPS_LATEST("disk-detect-zeroes");
+ DO_TEST_CAPS_LATEST("disk-discard_no_unref");
DO_TEST_CAPS_LATEST("disk-snapshot");
DO_TEST_CAPS_LATEST_PARSE_ERROR("disk-same-targets");
DO_TEST_CAPS_LATEST_PARSE_ERROR("disk-missing-target-invalid");
diff --git a/tests/qemuxml2xmloutdata/disk-discard_no_unref.x86_64-latest.xml b/tests/qemuxml2xmloutdata/disk-discard_no_unref.x86_64-latest.xml
new file mode 100644
index 0000000000..c57acf99dc
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/disk-discard_no_unref.x86_64-latest.xml
@@ -0,0 +1,42 @@
+<domain type='qemu'>
+ <name>test</name>
+ <uuid>92d7a226-cfae-425b-a6d3-00bbf9ec5c9e</uuid>
+ <memory unit='KiB'>1048576</memory>
+ <currentMemory unit='KiB'>1048576</currentMemory>
+ <vcpu placement='static'>1</vcpu>
+ <os>
+ <type arch='x86_64' machine='pc'>hvm</type>
+ <boot dev='cdrom'/>
+ <boot dev='hd'/>
+ <bootmenu enable='yes'/>
+ </os>
+ <cpu mode='custom' match='exact' check='none'>
+ <model fallback='forbid'>qemu64</model>
+ </cpu>
+ <clock offset='utc'/>
+ <on_poweroff>destroy</on_poweroff>
+ <on_reboot>restart</on_reboot>
+ <on_crash>restart</on_crash>
+ <devices>
+ <emulator>/usr/bin/qemu-system-x86_64</emulator>
+ <disk type='file' device='disk'>
+ <driver name='qemu' type='qcow2' discard='unmap' discard_no_unref='on'/>
+ <source file='/var/lib/libvirt/images/f14.img'/>
+ <target dev='vda' bus='virtio'/>
+ <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
+ </disk>
+ <controller type='usb' index='0' model='piix3-uhci'>
+ <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+ </controller>
+ <controller type='ide' index='0'>
+ <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+ </controller>
+ <controller type='pci' index='0' model='pci-root'/>
+ <input type='mouse' bus='ps2'/>
+ <input type='keyboard' bus='ps2'/>
+ <audio id='1' type='none'/>
+ <memballoon model='virtio'>
+ <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+ </memballoon>
+ </devices>
+</domain>
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index fb6fa3579f..6bdcb4bff5 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -599,6 +599,7 @@ mymain(void)
DO_TEST_CAPS_LATEST("disk-discard");
DO_TEST_CAPS_LATEST("disk-detect-zeroes");
+ DO_TEST_CAPS_LATEST("disk-discard_no_unref");
DO_TEST_NOCAPS("disk-serial");
--
2.40.1
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