[PATCH 1/1] conf: qemu 9pfs: add 'multidevs' option
Ján Tomko
jtomko at redhat.com
Thu Mar 19 13:10:26 UTC 2020
On a Tuesday in 2020, Christian Schoenebeck wrote:
>Introduce new 'multidevs' option for filesystem.
>
> <filesystem type='mount' accessmode='mapped' multidevs='remap'>
I don't like the 'multidevs' name, but cannot think of anything
beter.
'collisions' maybe?
> <source dir='/path'/>
> <target dir='mount_tag'>
> </filesystem>
>
>This option prevents misbheaviours on guest if a 9pfs export
>contains multiple devices, due to the potential file ID collisions
>this otherwise may cause.
>
>Signed-off-by: Christian Schoenebeck <qemu_oss at crudebyte.com>
>---
> docs/formatdomain.html.in | 47 ++++++++++++++++++++++++++++++++++-
> docs/schemas/domaincommon.rng | 10 ++++++++
> src/conf/domain_conf.c | 30 ++++++++++++++++++++++
> src/conf/domain_conf.h | 13 ++++++++++
> src/qemu/qemu_command.c | 7 ++++++
> 5 files changed, 106 insertions(+), 1 deletion(-)
Please split the XML changes from the qemu driver changes.
Also missing:
* qemu_capabilities addition
* qemuDomainDeviceDefValidateFS in qemu_domain.c - check for the capability,
reject this setting for virtiofs
* qemuxml2xmltest addition
* qemuxml2argvtest addition
(no changes required for virschematest - it checks all the XML files in
the directories used by the above tests against the schema)
>
>diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
>index 594146009d..13c506988b 100644
>--- a/docs/formatdomain.html.in
>+++ b/docs/formatdomain.html.in
>@@ -3967,7 +3967,7 @@
> <source name='my-vm-template'/>
> <target dir='/'/>
> </filesystem>
>- <filesystem type='mount' accessmode='passthrough'>
>+ <filesystem type='mount' accessmode='passthrough' multidevs='remap'>
> <driver type='path' wrpolicy='immediate'/>
> <source dir='/export/to/guest'/>
> <target dir='/import/from/host'/>
>@@ -4084,13 +4084,58 @@
> </dd>
> </dl>
>
>+ <p>
> <span class="since">Since 5.2.0</span>, the filesystem element
> has an optional attribute <code>model</code> with supported values
> "virtio-transitional", "virtio-non-transitional", or "virtio".
> See <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
> for more details.
>+ </p>
>+
Unrelated change that can be split out.
>+ <p>
>+ The filesystem element has an optional attribute <code>multidevs</code>
>+ which specifies how to deal with a filesystem export containing more than
>+ one device, in order to avoid file ID collisions on guest when using 9pfs
>+ (<span class="since">since 6.2.0, requires QEMU 4.2</span>).
>+ This attribute is not available for virtiofs. The possible values are:
>+ </p>
>+
>+ <dl>
>+ <dt><code>default</code></dt>
>+ <dd>
>+ Use QEMU's default setting (which currently is <code>warn</code>).
>+ </dd>
>+ <dt><code>remap</code></dt>
>+ <dd>
>+ This setting allows guest to access multiple devices per export without
>+ encountering misbehaviours. Inode numbers from host are automatically
>+ remapped on guest to actively prevent file ID collisions if guest
>+ accesses one export containing multiple devices.
>+ </dd>
>+ <dt><code>forbid</code></dt>
>+ <dd>
>+ Only allow to access one device per export by guest. Attempts to access
>+ additional devices on the same export will cause the individual
>+ filesystem access by guest to fail with an error and being logged (once)
>+ as error on host side.
>+ </dd>
>+ <dt><code>warn</code></dt>
>+ <dd>
>+ This setting resembles the behaviour of 9pfs prior to QEMU 4.2, that is
>+ no action is performed to prevent any potential file ID collisions if an
>+ export contains multiple devices, with the only exception: a warning is
>+ logged (once) on host side now. This setting may lead to misbehaviours
>+ on guest side if more than one device is exported per export, due to the
>+ potential file ID collisions this may cause on guest side in that case.
>+ </dd>
>+ </dl>
>+
> </dd>
>
>+ <p>
>+ The <code>filesystem</code> element may contain the following subelements:
>+ </p>
>+
And so can this one.
> <dt><code>driver</code></dt>
> <dd>
> The optional driver element allows specifying further details
>@@ -25422,6 +25449,9 @@ virDomainFSDefFormat(virBufferPtr buf,
> virBufferAsprintf(buf, " model='%s'",
> virDomainFSModelTypeToString(def->model));
> }
>+ if (def->multidevs) {
>+ virBufferAsprintf(buf, " multidevs='%s'", multidevs);
>+ }
make syntax-check complains here:
Curly brackets around single-line body:
../src/conf/domain_conf.c:25452-25454:
if (def->multidevs) {
virBufferAsprintf(buf, " multidevs='%s'", multidevs);
}
Jano
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