xemu/include/scsi/pr-manager.h
Paolo Bonzini 7c9e527659 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>
2017-09-22 01:06:51 +02:00

57 lines
1.4 KiB
C

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