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author | Paolo Bonzini <pbonzini@redhat.com> | 2017-08-21 18:58:56 +0200 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-09-22 01:06:51 +0200 |
commit | 7c9e527659c67d4d7b41d9504f93d2d7ee482488 (patch) | |
tree | 2f604a8ad523e8cf9217b464344900f86d0bbfba /qapi | |
parent | 092aa2fc65b7a35121616aad8f39d47b8f921618 (diff) |
scsi, file-posix: add support for persistent reservation management
It is a common requirement for virtual machine to send persistent
reservations, but this currently requires either running QEMU with
CAP_SYS_RAWIO, or using out-of-tree patches that let an unprivileged
QEMU bypass Linux's filter on SG_IO commands.
As an alternative mechanism, the next patches will introduce a
privileged helper to run persistent reservation commands without
expanding QEMU's attack surface unnecessarily.
The helper is invoked through a "pr-manager" QOM object, to which
file-posix.c passes SG_IO requests for PERSISTENT RESERVE OUT and
PERSISTENT RESERVE IN commands. For example:
$ qemu-system-x86_64
-device virtio-scsi \
-object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
-drive if=none,id=hd,driver=raw,file.filename=/dev/sdb,file.pr-manager=helper0
-device scsi-block,drive=hd
or:
$ qemu-system-x86_64
-device virtio-scsi \
-object pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock
-blockdev node-name=hd,driver=raw,file.driver=host_device,file.filename=/dev/sdb,file.pr-manager=helper0
-device scsi-block,drive=hd
Multiple pr-manager implementations are conceivable and possible, though
only one is implemented right now. For example, a pr-manager could:
- talk directly to the multipath daemon from a privileged QEMU
(i.e. QEMU links to libmpathpersist); this makes reservation work
properly with multipath, but still requires CAP_SYS_RAWIO
- use the Linux IOC_PR_* ioctls (they require CAP_SYS_ADMIN though)
- more interestingly, implement reservations directly in QEMU
through file system locks or a shared database (e.g. sqlite)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'qapi')
-rw-r--r-- | qapi/block-core.json | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/qapi/block-core.json b/qapi/block-core.json index bb11815608..c69a395804 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -2241,6 +2241,9 @@ # Driver specific block device options for the file backend. # # @filename: path to the image file +# @pr-manager: the id for the object that will handle persistent reservations +# for this device (default: none, forward the commands via SG_IO; +# since 2.11) # @aio: AIO backend (default: threads) (since: 2.8) # @locking: whether to enable file locking. If set to 'auto', only enable # when Open File Descriptor (OFD) locking API is available @@ -2250,6 +2253,7 @@ ## { 'struct': 'BlockdevOptionsFile', 'data': { 'filename': 'str', + '*pr-manager': 'str', '*locking': 'OnOffAuto', '*aio': 'BlockdevAioOptions' } } |