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@xxxxxxxxxxxxx> --- 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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