11:36 a.m.
Adam Litke has been asking if I can expose watermark information from
qemu when doing block commit. Qemu still doesn't expose that
information when doing 'virsh blockcopy' (QMP drive-mirror), but DOES
expose it for regular and active 'virsh blockcommit'. The idea is that
when you are writing to more than one file at a time, management needs
to know if the file is nearing a watermark for usage that necessitates
growing the storage volume before hitting an ENOSPC error. In
particular, Adam's use is running qcow2 format on top of block devices,
where it is easy to enlarge the block device.
The current libvirt API virDomainBlockInfo() can only get watermark
information for the active image in a disk chain. It shows three numbers:
capacity: the disk size seen by the guest (can be grown via
virt-resize) - usually larger than the host block device if the guest
has not used the complete disk, but can also be smaller than the host
block device due to overhead of qcow2 and the disk is mostly in use
allocation: the known usage of the host file/block device, should never
be larger than the physical size (other than rounding up to file sector
sizing). For sparse files, this number is smaller than total size based
by the amount of holes in the file. For block devices with qcow2 format,
this number is reported by qemu as the maximum offset in use by the
qcow2 file (without regards to whether earlier offsets are holes that
could be reused). Compare this to what 'du' would report.
physical: the total size of the host file/block device. Compare this to
what 'ls' would report.
Also, the libvirt API virStorageVolGetXMLDesc reports two of those
numbers for a top-level image: <capacity> and <allocation> are listed as
siblings of <target>. But it is not present for a <backingStore>; you
have to use the API twice.
Now that we have a common virStorageSourcePtr type in the C code, we
could do a better job of exposing full information for the entire chain
in a single API call.
I've got a couple ideas of where we can extend existing APIs (and the
extensions do not involve bumping the .so versioning, so it can also be
backported, although it gets MUCH harder to backport without
virStorageSourcePtr).
First, I think the virStorageVolGetXMLDesc should show all three
numbers, by adding a <physical unit='bytes'>...</physical> element
alongside the existing <capacity> and <allocation> elements. Also, I
think it might be nice if we could enhance the API to do a full chain
recursion (probably requires an explicit flag to turn on) where it shows
details on the full backing chain, rather than just partial details on
the immediate backing file; in doing that, the <backingStore> element
would gain recursive <backingStore> (similar to what we recently did in
<domain> XML). In that mode, each layer of <backingStore> would also
report <capacity>, <allocation>, and <physical>. Something like:
# virsh vol-dumpxml --pool default f20.snap2
<volume type='file'>
<name>f20.snap2</name>
<key>/var/lib/libvirt/images/f20.snap2</key>
<source>
</source>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<target>
<path>/var/lib/libvirt/images/f20.snap2</path>
<format type='qcow2'/>
<permissions>
<mode>0600</mode>
<owner>0</owner>
<group>0</group>
<label>system_u:object_r:virt_image_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.583411967</atime>
<mtime>1403064822.622766566</mtime>
<ctime>1404318525.899951254</ctime>
</timestamps>
<compat>1.1</compat>
<features/>
</target>
<backingStore>
<path>/var/lib/libvirt/images/f20.snap1</path>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<format type='qcow2'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<compat>1.1</compat>
<features/>
<backingStore>
<path>/var/lib/libvirt/images/f20.base</path>
<capacity unit='bytes'>10737418240</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>10737418240</allocation>
<format type='raw'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore/>
</backingStore>
</backingStore>
</volume>
Also, the current storage volume API is rather hard-coded to assume that
backing elements are in the same storage pool, which is not always true.
It may be time to introduce <backingStore type='file'> or <backingStore
type='network'> to allow better details of cross-pool backing elements,
while leaving plain <backingStore> as a back-compat synonym for
<backingStore type='volume'> for the current hard-coded layout that
assumes the backing element is in the same storage pool.
The other idea I've had is to expand the <domain> XML to expose more
information about backing chains, including to make it expose details
that are redundant with virDomainBlockInfo() for the top level, or maybe
even what virDomainBlockStatsFlags() reports. Here, we have a bit of a
choice - storage volume XML was inconsistent on which attributes were
siblings to <target> (such as <capacity>) vs. children (such as
<timestamps>); it might be nicer to stick all per-file elements at the
same level in <disk> XML (probably as siblings to <source>). On the
other hand, I strongly feel that <compat> is a feature of the <format>,
so it should have been a child rather than a sibling. So, as an example
of what the XML might look like:
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'>
<compat>1.1</compat>
<features/>
</driver>
<source file='/tmp/snap2.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore type='file' index='1'>
<format type='qcow2'>
<compat>1.1</compat>
<features/>
</format>
<source file='/tmp/snap1.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>0</owner>
<group>0</group>
<label>system_u:object_r:virt_image_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.583411967</atime>
<mtime>1403064822.622766566</mtime>
<ctime>1404318525.899951254</ctime>
</timestamps>
<backingStore type='file' index='2'>
<format type='raw'/>
<capacity unit='bytes'>10737418240</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>10737418240</allocation>
<source file='/tmp/base.img'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vda' bus='virtio'/>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03'
function='0x0'/>
</disk>
Again, this is a lot of new information, so it may be wise to add a new
flag that must be turned on to request the information. But adding this
information would allow watermark tracking for a blockcommit operation -
when collapsing 'base <- snap1 <- snap2' into 'base <- snap2' by
committing snap1 into base, the <allocation> sublement of the
appropriate <backingStore> level will do live tracking of the qemu
values as more data is being written into base, and thus be usable to
determine if the block device behind base needs to be externally
expanded before hitting an ENOSPC situation.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
12:31 p.m.
On 06/08/14 10:36 -0600, Eric Blake wrote:
Adam Litke has been asking if I can expose watermark information from
qemu when doing block commit. Qemu still doesn't expose that
information when doing 'virsh blockcopy' (QMP drive-mirror), but DOES
expose it for regular and active 'virsh blockcommit'. The idea is that
when you are writing to more than one file at a time, management needs
to know if the file is nearing a watermark for usage that necessitates
growing the storage volume before hitting an ENOSPC error. In
particular, Adam's use is running qcow2 format on top of block devices,
where it is easy to enlarge the block device.
The current libvirt API virDomainBlockInfo() can only get watermark
information for the active image in a disk chain. It shows three numbers:
capacity: the disk size seen by the guest (can be grown via
virt-resize) - usually larger than the host block device if the guest
has not used the complete disk, but can also be smaller than the host
block device due to overhead of qcow2 and the disk is mostly in use
allocation: the known usage of the host file/block device, should never
be larger than the physical size (other than rounding up to file sector
sizing). For sparse files, this number is smaller than total size based
by the amount of holes in the file. For block devices with qcow2 format,
this number is reported by qemu as the maximum offset in use by the
qcow2 file (without regards to whether earlier offsets are holes that
could be reused). Compare this to what 'du' would report.
physical: the total size of the host file/block device. Compare this to
what 'ls' would report.
Also, the libvirt API virStorageVolGetXMLDesc reports two of those
numbers for a top-level image: <capacity> and <allocation> are listed as
siblings of <target>. But it is not present for a <backingStore>; you
have to use the API twice.
Now that we have a common virStorageSourcePtr type in the C code, we
could do a better job of exposing full information for the entire chain
in a single API call.
I've got a couple ideas of where we can extend existing APIs (and the
extensions do not involve bumping the .so versioning, so it can also be
backported, although it gets MUCH harder to backport without
virStorageSourcePtr).
First, I think the virStorageVolGetXMLDesc should show all three
numbers, by adding a <physical unit='bytes'>...</physical> element
alongside the existing <capacity> and <allocation> elements. Also, I
This seems like an obvious improvement especially to make the APIs
more symetric.
think it might be nice if we could enhance the API to do a full chain
recursion (probably requires an explicit flag to turn on) where it shows
details on the full backing chain, rather than just partial details on
the immediate backing file; in doing that, the <backingStore> element
would gain recursive <backingStore> (similar to what we recently did in
<domain> XML). In that mode, each layer of <backingStore> would also
report <capacity>, <allocation>, and <physical>. Something like:
+1
# virsh vol-dumpxml --pool default f20.snap2
<volume type='file'>
<name>f20.snap2</name>
<key>/var/lib/libvirt/images/f20.snap2</key>
<source>
</source>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<target>
<path>/var/lib/libvirt/images/f20.snap2</path>
<format type='qcow2'/>
<permissions>
<mode>0600</mode>
<owner>0</owner>
<group>0</group>
<label>system_u:object_r:virt_image_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.583411967</atime>
<mtime>1403064822.622766566</mtime>
<ctime>1404318525.899951254</ctime>
</timestamps>
<compat>1.1</compat>
<features/>
</target>
<backingStore>
<path>/var/lib/libvirt/images/f20.snap1</path>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<format type='qcow2'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<compat>1.1</compat>
<features/>
<backingStore>
<path>/var/lib/libvirt/images/f20.base</path>
<capacity unit='bytes'>10737418240</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>10737418240</allocation>
<format type='raw'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore/>
</backingStore>
</backingStore>
</volume>
Also, the current storage volume API is rather hard-coded to assume that
backing elements are in the same storage pool, which is not always true.
It may be time to introduce <backingStore type='file'> or <backingStore
type='network'> to allow better details of cross-pool backing elements,
Would you also need to add a <pool>default</pool> element in each one
so that you can name the pool explicitly?
while leaving plain <backingStore> as a back-compat synonym for
<backingStore type='volume'> for the current hard-coded layout that
assumes the backing element is in the same storage pool.
The other idea I've had is to expand the <domain> XML to expose more
information about backing chains, including to make it expose details
that are redundant with virDomainBlockInfo() for the top level, or maybe
even what virDomainBlockStatsFlags() reports. Here, we have a bit of a
choice - storage volume XML was inconsistent on which attributes were
siblings to <target> (such as <capacity>) vs. children (such as
<timestamps>); it might be nicer to stick all per-file elements at the
same level in <disk> XML (probably as siblings to <source>). On the
other hand, I strongly feel that <compat> is a feature of the <format>,
so it should have been a child rather than a sibling. So, as an example
of what the XML might look like:
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'>
<compat>1.1</compat>
<features/>
</driver>
<source file='/tmp/snap2.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore type='file' index='1'>
<format type='qcow2'>
<compat>1.1</compat>
<features/>
</format>
<source file='/tmp/snap1.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>0</owner>
<group>0</group>
<label>system_u:object_r:virt_image_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.583411967</atime>
<mtime>1403064822.622766566</mtime>
<ctime>1404318525.899951254</ctime>
</timestamps>
<backingStore type='file' index='2'>
<format type='raw'/>
<capacity unit='bytes'>10737418240</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>10737418240</allocation>
<source file='/tmp/base.img'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vda' bus='virtio'/>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03'
function='0x0'/>
</disk>
Again, this is a lot of new information, so it may be wise to add a new
flag that must be turned on to request the information. But adding this
information would allow watermark tracking for a blockcommit operation -
when collapsing 'base <- snap1 <- snap2' into 'base <- snap2' by
committing snap1 into base, the <allocation> sublement of the
appropriate <backingStore> level will do live tracking of the qemu
values as more data is being written into base, and thus be usable to
determine if the block device behind base needs to be externally
expanded before hitting an ENOSPC situation.
Yes, +1 and this would satisfy my use case.
--
Adam Litke
4:57 a.m.
On 08/06/14 18:36, Eric Blake wrote:
Adam Litke has been asking if I can expose watermark information
from\
<bikeshedding>
I'd be glad if we stopped calling this watermark. The wiki
disambiguation article states:
<citation>
A watermark is a recognizable image or pattern in paper used to identify
authenticity.
Watermark or watermarking can also refer to:
In digital watermarks and digital security[edit]
Watermark (data file), a method for ensuring data integrity which
combines aspects of data hashing and digital watermarking
Watermark (data synchronization), directory synchronization related
programming terminology
High-water mark (computer security), network security terminology
Audio watermark, techniques for detecting hidden information from
watermarked signal
Digital watermarking, a technique to embed data in digital audio, images
or video
Watermarking attack, an attack on disk encryption methods
</citation>
As this usage is neither of those I always have to translate it to
something more sane when discussing this topic. I actually like the
subject of this mail to refer to what's discussed here. I'm not sure
though if we can come up with a shorter name that will not be ambiguous
with something else.
</bikeshedding>
qemu when doing block commit. Qemu still doesn't expose that
information when doing 'virsh blockcopy' (QMP drive-mirror), but DOES
expose it for regular and active 'virsh blockcommit'. The idea is that
when you are writing to more than one file at a time, management needs
to know if the file is nearing a watermark for usage that necessitates
growing the storage volume before hitting an ENOSPC error. In
particular, Adam's use is running qcow2 format on top of block devices,
where it is easy to enlarge the block device.
The current libvirt API virDomainBlockInfo() can only get watermark
information for the active image in a disk chain. It shows three numbers:
capacity: the disk size seen by the guest (can be grown via
virt-resize) - usually larger than the host block device if the guest
has not used the complete disk, but can also be smaller than the host
block device due to overhead of qcow2 and the disk is mostly in use
allocation: the known usage of the host file/block device, should never
be larger than the physical size (other than rounding up to file sector
sizing). For sparse files, this number is smaller than total size based
by the amount of holes in the file. For block devices with qcow2 format,
this number is reported by qemu as the maximum offset in use by the
qcow2 file (without regards to whether earlier offsets are holes that
could be reused). Compare this to what 'du' would report.
physical: the total size of the host file/block device. Compare this to
what 'ls' would report.
Also, the libvirt API virStorageVolGetXMLDesc reports two of those
numbers for a top-level image: <capacity> and <allocation> are listed as
siblings of <target>. But it is not present for a <backingStore>; you
have to use the API twice.
Now that we have a common virStorageSourcePtr type in the C code, we
could do a better job of exposing full information for the entire chain
in a single API call.
I've got a couple ideas of where we can extend existing APIs (and the
extensions do not involve bumping the .so versioning, so it can also be
backported, although it gets MUCH harder to backport without
virStorageSourcePtr).
First, I think the virStorageVolGetXMLDesc should show all three
numbers, by adding a <physical unit='bytes'>...</physical> element
alongside the existing <capacity> and <allocation> elements. Also, I
think it might be nice if we could enhance the API to do a full chain
recursion (probably requires an explicit flag to turn on) where it shows
details on the full backing chain, rather than just partial details on
the immediate backing file; in doing that, the <backingStore> element
would gain recursive <backingStore> (similar to what we recently did in
<domain> XML). In that mode, each layer of <backingStore> would also
report <capacity>, <allocation>, and <physical>. Something like:
While this is certainly a improvement to the storage volume API, it will
not help Adam much as oVirt isn't actually using the storage driver.
# virsh vol-dumpxml --pool default f20.snap2
<volume type='file'>
...
Also, the current storage volume API is rather hard-coded to assume that
backing elements are in the same storage pool, which is not always true.
It may be time to introduce <backingStore type='file'> or
<backingStore
type='network'> to allow better details of cross-pool backing elements,
while leaving plain <backingStore> as a back-compat synonym for
<backingStore type='volume'> for the current hard-coded layout that
assumes the backing element is in the same storage pool.
That would certainly improve the usability, but as said it would not
help oVirt that much.
The other idea I've had is to expand the <domain> XML to expose more
information about backing chains, including to make it expose details
that are redundant with virDomainBlockInfo() for the top level, or maybe
even what virDomainBlockStatsFlags() reports. Here, we have a bit of a
choice - storage volume XML was inconsistent on which attributes were
siblings to <target> (such as <capacity>) vs. children (such as
<timestamps>); it might be nicer to stick all per-file elements at the
same level in <disk> XML (probably as siblings to <source>). On the
other hand, I strongly feel that <compat> is a feature of the <format>,
so it should have been a child rather than a sibling. So, as an example
of what the XML might look like:
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'>
<compat>1.1</compat>
<features/>
</driver>
<source file='/tmp/snap2.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
Both <permissions> and <timestamps> are not entirely useful information
in runtime.
<backingStore type='file' index='1'>
<format type='qcow2'>
<compat>1.1</compat>
<features/>
</format>
<source file='/tmp/snap1.img'/>
<capacity unit='bytes'>12884901888</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>2503548928</allocation>
<permissions>
<mode>0600</mode>
<owner>0</owner>
<group>0</group>
<label>system_u:object_r:virt_image_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.583411967</atime>
<mtime>1403064822.622766566</mtime>
<ctime>1404318525.899951254</ctime>
</timestamps>
<backingStore type='file' index='2'>
<format type='raw'/>
<capacity unit='bytes'>10737418240</capacity>
<allocation unit='bytes'>2503548928</allocation>
<physical unit='bytes'>10737418240</allocation>
<source file='/tmp/base.img'/>
<permissions>
<mode>0600</mode>
<owner>107</owner>
<group>107</group>
<label>system_u:object_r:virt_content_t:s0</label>
</permissions>
<timestamps>
<atime>1407295598.623411816</atime>
<mtime>1402005765.810488875</mtime>
<ctime>1404318523.313955796</ctime>
</timestamps>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vda' bus='virtio'/>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x03'
function='0x0'/>
</disk>
Again, this is a lot of new information, so it may be wise to add a new
flag that must be turned on to request the information. But adding this
This definitely needs a flag. We are polluting the XML enough by the
backing chain now.
information would allow watermark tracking for a blockcommit
operation -
when collapsing 'base <- snap1 <- snap2' into 'base <- snap2'
by
committing snap1 into base, the <allocation> sublement of the
appropriate <backingStore> level will do live tracking of the qemu
values as more data is being written into base, and thus be usable to
determine if the block device behind base needs to be externally
expanded before hitting an ENOSPC situation.
Peter
4:30 p.m.
[revisiting something that finally surfaced to the top of my todo list]
On 08/07/2014 03:57 AM, Peter Krempa wrote:
On 08/06/14 18:36, Eric Blake wrote:
> Adam Litke has been asking if I can expose watermark information from\
<bikeshedding>
I'd be glad if we stopped calling this watermark. The wiki
disambiguation article states:
<citation>
A watermark is a recognizable image or pattern in paper used to identify
authenticity.
Watermark or watermarking can also refer to:
In digital watermarks and digital security[edit]
Watermark (data file), a method for ensuring data integrity which
combines aspects of data hashing and digital watermarking
Watermark (data synchronization), directory synchronization related
programming terminology
High-water mark (computer security),
We are using it in the sense of high-water mark. Etymology-wise, it
goes back to the days of loading boats - you would paint a line called
the high watermark; as the boat was weighed down with more cargo, you
had to stop loading when that line touched the water, or risk sinking
the boat. In the same vein, someone running on expandable underlying
storage can let the guest consume until it hits the watermark, at which
point the storage must be grown to avoid sinking the guest with an
out-of-space event.
But I'm open to the idea of any other terminology... For now, calling
it allocation is good enough, since that is the term I will be putting
in the XML.
>
> The other idea I've had is to expand the <domain> XML to expose more
> information about backing chains, including to make it expose details
> that are redundant with virDomainBlockInfo() for the top level, or maybe
> even what virDomainBlockStatsFlags() reports. Here, we have a bit of a
> choice - storage volume XML was inconsistent on which attributes were
> siblings to <target> (such as <capacity>) vs. children (such as
> <timestamps>); it might be nicer to stick all per-file elements at the
> same level in <disk> XML (probably as siblings to <source>). On the
> other hand, I strongly feel that <compat> is a feature of the <format>,
> so it should have been a child rather than a sibling. So, as an example
> of what the XML might look like:
>
> <disk type='file' device='disk'>
> <driver name='qemu' type='qcow2'>
> <compat>1.1</compat>
> <features/>
> </driver>
> <source file='/tmp/snap2.img'/>
> <capacity unit='bytes'>12884901888</capacity>
> <allocation unit='bytes'>2503548928</allocation>
> <physical unit='bytes'>2503548928</allocation>
> <permissions>
> <mode>0600</mode>
> <owner>107</owner>
> <group>107</group>
> <label>system_u:object_r:virt_content_t:s0</label>
> </permissions>
> <timestamps>
> <atime>1407295598.623411816</atime>
> <mtime>1402005765.810488875</mtime>
> <ctime>1404318523.313955796</ctime>
> </timestamps>
Both <permissions> and <timestamps> are not entirely useful information
in runtime.
Maybe not entirely useful, but fairly easy to learn and awfully similar
to storage volume XML. But we can do this incrementally, the real
request I have is for allocation; and while I think permissions and
timestamps may be useful to shave off later API calls, I don't think it
is a showstopper if they are not present in the first cut that adds
allocation.
>
> Again, this is a lot of new information, so it may be wise to add a new
> flag that must be turned on to request the information. But adding this
This definitely needs a flag. We are polluting the XML enough by the
backing chain now.
Okay, I'll be proposing a patch with the new flag shortly.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
2:29 a.m.
On 09/12/14 23:30, Eric Blake wrote:
[revisiting something that finally surfaced to the top of my todo
list]
On 08/07/2014 03:57 AM, Peter Krempa wrote:
> On 08/06/14 18:36, Eric Blake wrote:
>> Adam Litke has been asking if I can expose watermark information from\
>
> <bikeshedding>
> I'd be glad if we stopped calling this watermark. The wiki
> disambiguation article states:
>
> <citation>
> A watermark is a recognizable image or pattern in paper used to identify
> authenticity.
>
> Watermark or watermarking can also refer to:
>
> In digital watermarks and digital security[edit]
> Watermark (data file), a method for ensuring data integrity which
> combines aspects of data hashing and digital watermarking
> Watermark (data synchronization), directory synchronization related
> programming terminology
> High-water mark (computer security),
We are using it in the sense of high-water mark. Etymology-wise, it
goes back to the days of loading boats - you would paint a line called
the high watermark; as the boat was weighed down with more cargo, you
had to stop loading when that line touched the water, or risk sinking
the boat. In the same vein, someone running on expandable underlying
storage can let the guest consume until it hits the watermark, at which
point the storage must be grown to avoid sinking the guest with an
out-of-space event.
But I'm open to the idea of any other terminology... For now, calling
it allocation is good enough, since that is the term I will be putting
in the XML.
I think that allocation is fine. High-water mark might be acceptable but
still looks a bit awkward to me.
Peter
9:05 a.m.
On 16/09/14 09:29 +0200, Peter Krempa wrote:
On 09/12/14 23:30, Eric Blake wrote:
> [revisiting something that finally surfaced to the top of my todo list]
>
> On 08/07/2014 03:57 AM, Peter Krempa wrote:
>> On 08/06/14 18:36, Eric Blake wrote:
>>> Adam Litke has been asking if I can expose watermark information from\
>>
>> <bikeshedding>
>> I'd be glad if we stopped calling this watermark. The wiki
>> disambiguation article states:
>>
>> <citation>
>> A watermark is a recognizable image or pattern in paper used to identify
>> authenticity.
>>
>> Watermark or watermarking can also refer to:
>>
>> In digital watermarks and digital security[edit]
>> Watermark (data file), a method for ensuring data integrity which
>> combines aspects of data hashing and digital watermarking
>> Watermark (data synchronization), directory synchronization related
>> programming terminology
>> High-water mark (computer security),
>
> We are using it in the sense of high-water mark. Etymology-wise, it
> goes back to the days of loading boats - you would paint a line called
> the high watermark; as the boat was weighed down with more cargo, you
> had to stop loading when that line touched the water, or risk sinking
> the boat. In the same vein, someone running on expandable underlying
> storage can let the guest consume until it hits the watermark, at which
> point the storage must be grown to avoid sinking the guest with an
> out-of-space event.
>
> But I'm open to the idea of any other terminology... For now, calling
> it allocation is good enough, since that is the term I will be putting
> in the XML.
>
I think that allocation is fine. High-water mark might be acceptable but
still looks a bit awkward to me.
I also prefer 'allocation' since it describes the piece of information
being presented rather than something which it might be used for.
--
Adam Litke
3755
days inactive
3796
days old
5 comments
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