Re: [PATCH 1/1] conf: qemu 9pfs: add 'multidevs' option

Introduce new 'multidevs' option for filesystem. <filesystem type='mount' accessmode='mapped' multidevs='remap'>

<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(a)crudebyte.com&gt; --- 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(-)

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 @@ &lt;source name='my-vm-template'/&gt; &lt;target dir='/'/&gt; &lt;/filesystem&gt; - &lt;filesystem type='mount' accessmode='passthrough'&gt; + &lt;filesystem type='mount' accessmode='passthrough' multidevs='remap'&gt; &lt;driver type='path' wrpolicy='immediate'/&gt; &lt;source dir='/export/to/guest'/&gt; &lt;target dir='/import/from/host'/&gt; @@ -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> +

+ <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> +

<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); + }