On a Monday in 2020, Christian Schoenebeck wrote:
QEMU 4.2 added a new option 'multidevs' for 9pfs. The following patch adds support for this new option to libvirt. In short, what is this about: to distinguish files uniquely from each other in general, numeric file IDs are typically used for comparison, which in practice is the combination of a file's device ID and the file's inode number. Unfortunately 9p protocol's QID field used for this purpose, currently is too small to fit both the device ID and inode number in, which hence is a problem if one 9pfs export contains multiple devices and may thus lead to misbheaviours on guest (e.g. with SAMBA file servers) in that case due to potential file ID collisions. To mitigate this problem with 9pfs a 'multidevs' option was introduced in QEMU 4.2 for defining how to deal with this, e.g. multidevs=remap will cause QEMU's 9pfs implementation to remap all inodes from host side to different inode numbers on guest side in a way that prevents file ID collisions. NOTE: In the libvirt docs changes of this libvirt patch I simply assumed "since 6.2.0". So the final libvirt version number would need to be adjusted in that text if necessary. See QEMU discussion with following Message-ID for details: 8a2ffe17fda3a86b9a5a437e1245276881f1e235.1567680121.git.qemu_oss@xxxxxxxxxxxxx v2->v3: * Rebased to master (SHA-1 e4bf03b8ff). * Auto sense QEMU capability for command line option fsdev.multidevs instead of checking for QEMU version 4.2. [patch 1] * Auto regenerated capabilities data for all archs (fixes capability test). [patch 1] * Added XML test. [patch 2] * Added argv test. [patch 3] Message-ID of v2: cover.1584723662.git.qemu_oss@xxxxxxxxxxxxx Christian Schoenebeck (3): qemu: capabilities: add QEMU_CAPS_VIRTFS_MULTIDEVS conf: add 'multidevs' option qemu: add support for 'multidevs' option docs/formatdomain.html.in | 40 ++++++++++++- docs/schemas/domaincommon.rng | 10 ++++ src/conf/domain_conf.c | 29 ++++++++++ src/conf/domain_conf.h | 13 +++++ src/qemu/qemu_capabilities.c | 2 + src/qemu/qemu_capabilities.h | 1 + src/qemu/qemu_command.c | 7 +++ src/qemu/qemu_domain.c | 12 ++++ .../caps_4.2.0.aarch64.xml | 1 + .../qemucapabilitiesdata/caps_4.2.0.s390x.xml | 1 + .../caps_4.2.0.x86_64.xml | 1 + .../caps_5.0.0.aarch64.xml | 1 + .../qemucapabilitiesdata/caps_5.0.0.ppc64.xml | 1 + .../caps_5.0.0.x86_64.xml | 1 + .../virtio-9p-multidevs.x86_64-latest.args | 45 +++++++++++++++ .../qemuxml2argvdata/virtio-9p-multidevs.xml | 53 ++++++++++++++++++ tests/qemuxml2argvtest.c | 2 + .../virtio-9p-multidevs.x86_64-latest.xml | 56 +++++++++++++++++++ tests/qemuxml2xmltest.c | 2 + 19 files changed, 277 insertions(+), 1 deletion(-) create mode 100644 tests/qemuxml2argvdata/virtio-9p-multidevs.x86_64-latest.args create mode 100644 tests/qemuxml2argvdata/virtio-9p-multidevs.xml create mode 100644 tests/qemuxml2xmloutdata/virtio-9p-multidevs.x86_64-latest.xml
Reviewed-by: Ján Tomko <jtomko@xxxxxxxxxx> Jano
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