7c9e527659
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>
57 lines
1.4 KiB
C
57 lines
1.4 KiB
C
#ifndef PR_MANAGER_H
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#define PR_MANAGER_H
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#include "qom/object.h"
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#include "qapi/qmp/qdict.h"
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#include "qapi/visitor.h"
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#include "qom/object_interfaces.h"
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#include "block/aio.h"
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#define TYPE_PR_MANAGER "pr-manager"
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#define PR_MANAGER_CLASS(klass) \
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OBJECT_CLASS_CHECK(PRManagerClass, (klass), TYPE_PR_MANAGER)
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#define PR_MANAGER_GET_CLASS(obj) \
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OBJECT_GET_CLASS(PRManagerClass, (obj), TYPE_PR_MANAGER)
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#define PR_MANAGER(obj) \
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OBJECT_CHECK(PRManager, (obj), TYPE_PR_MANAGER)
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struct sg_io_hdr;
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typedef struct PRManager {
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/* <private> */
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Object parent;
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} PRManager;
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/**
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* PRManagerClass:
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* @parent_class: the base class
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* @run: callback invoked in thread pool context
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*/
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typedef struct PRManagerClass {
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/* <private> */
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ObjectClass parent_class;
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/* <public> */
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int (*run)(PRManager *pr_mgr, int fd, struct sg_io_hdr *hdr);
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} PRManagerClass;
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BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
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AioContext *ctx, int fd,
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struct sg_io_hdr *hdr,
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BlockCompletionFunc *complete,
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void *opaque);
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#ifdef CONFIG_LINUX
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PRManager *pr_manager_lookup(const char *id, Error **errp);
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#else
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static inline PRManager *pr_manager_lookup(const char *id, Error **errp)
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{
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/* The classes do not exist at all! */
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error_setg(errp, "No persistent reservation manager with id '%s'", id);
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return NULL;
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}
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#endif
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#endif
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