Introduce new 'multidevs' option for filesystem.
<filesystem type='mount' accessmode='mapped' multidevs='remap'>
<source dir='/path'/>
<target dir='mount_tag'>
</filesystem>
This option prevents misbehaviours on guest if a qemu 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 | 40 ++++++++++++++++++++++++++++++++++-
docs/schemas/domaincommon.rng | 10 +++++++++
src/conf/domain_conf.c | 29 +++++++++++++++++++++++++
src/conf/domain_conf.h | 13 ++++++++++++
4 files changed, 91 insertions(+), 1 deletion(-)
diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index cc2c671c14..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'/>
@@ -4092,6 +4092,44 @@
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>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 6805420451..9b37740e30 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -2676,6 +2676,16 @@
</choice>
</attribute>
</optional>
+ <optional>
+ <attribute name="multidevs">
+ <choice>
+ <value>default</value>
+ <value>remap</value>
+ <value>forbid</value>
+ <value>warn</value>
+ </choice>
+ </attribute>
+ </optional>
<optional>
<element name='readonly'>
<empty/>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 71535f53f5..6a9a7dd0bb 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -501,6 +501,14 @@ VIR_ENUM_IMPL(virDomainFSModel,
"virtio-non-transitional",
);
+VIR_ENUM_IMPL(virDomainFSMultidevs,
+ VIR_DOMAIN_FS_MULTIDEVS_LAST,
+ "default",
+ "remap",
+ "forbid",
+ "warn",
+);
+
VIR_ENUM_IMPL(virDomainFSCacheMode,
VIR_DOMAIN_FS_CACHE_MODE_LAST,
"default",
@@ -11376,6 +11384,7 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
g_autofree char *usage = NULL;
g_autofree char *units = NULL;
g_autofree char *model = NULL;
+ g_autofree char *multidevs = NULL;
ctxt->node = node;
@@ -11414,6 +11423,17 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
}
}
+ multidevs = virXMLPropString(node, "multidevs");
+ if (multidevs) {
+ if ((def->multidevs = virDomainFSMultidevsTypeFromString(multidevs)) < 0) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+ _("unknown multidevs '%s'"), multidevs);
+ goto error;
+ }
+ } else {
+ def->multidevs = VIR_DOMAIN_FS_MULTIDEVS_DEFAULT;
+ }
+
if (virDomainParseScaledValue("./space_hard_limit[1]",
NULL, ctxt, &def->space_hard_limit,
1, ULLONG_MAX, false) < 0)
@@ -25397,6 +25417,7 @@ virDomainFSDefFormat(virBufferPtr buf,
const char *accessmode = virDomainFSAccessModeTypeToString(def->accessmode);
const char *fsdriver = virDomainFSDriverTypeToString(def->fsdriver);
const char *wrpolicy = virDomainFSWrpolicyTypeToString(def->wrpolicy);
+ const char *multidevs = virDomainFSMultidevsTypeToString(def->multidevs);
const char *src = def->src->path;
g_auto(virBuffer) driverAttrBuf = VIR_BUFFER_INITIALIZER;
g_auto(virBuffer) driverBuf = VIR_BUFFER_INIT_CHILD(buf);
@@ -25415,6 +25436,12 @@ virDomainFSDefFormat(virBufferPtr buf,
return -1;
}
+ if (!multidevs) {
+ virReportError(VIR_ERR_INTERNAL_ERROR,
+ _("unexpected multidevs %d"), def->multidevs);
+ return -1;
+ }
+
virBufferAsprintf(buf,
"<filesystem type='%s' accessmode='%s'",
type, accessmode);
@@ -25422,6 +25449,8 @@ virDomainFSDefFormat(virBufferPtr buf,
virBufferAsprintf(buf, " model='%s'",
virDomainFSModelTypeToString(def->model));
}
+ if (def->multidevs)
+ virBufferAsprintf(buf, " multidevs='%s'", multidevs);
virBufferAddLit(buf, ">\n");
virBufferAdjustIndent(buf, 2);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 91b776c28a..23b7924781 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -796,6 +796,18 @@ typedef enum {
VIR_DOMAIN_FS_WRPOLICY_LAST
} virDomainFSWrpolicy;
+/* How to handle exports containing multiple devices. */
+typedef enum {
+ VIR_DOMAIN_FS_MULTIDEVS_DEFAULT = 0, /* Use QEMU's default setting */
+ VIR_DOMAIN_FS_MULTIDEVS_REMAP, /* Remap inodes from host to guest */
+ VIR_DOMAIN_FS_MULTIDEVS_FORBID, /* Prohibit more than one device */
+ VIR_DOMAIN_FS_MULTIDEVS_WARN, /* Just log a warning if multiple devices */
+
+ VIR_DOMAIN_FS_MULTIDEVS_LAST
+} virDomainFSMultidevs;
+
+VIR_ENUM_DECL(virDomainFSMultidevs);
+
typedef enum {
VIR_DOMAIN_FS_MODEL_DEFAULT = 0,
VIR_DOMAIN_FS_MODEL_VIRTIO,
@@ -820,6 +832,7 @@ struct _virDomainFSDef {
int wrpolicy; /* enum virDomainFSWrpolicy */
int format; /* virStorageFileFormat */
int model; /* virDomainFSModel */
+ int multidevs; /* virDomainFSMultidevs */
unsigned long long usage; /* in bytes */
virStorageSourcePtr src;
char *dst;
--
2.20.1
