qemu/scsi/pr-manager.c
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

110 lines
2.6 KiB
C

/*
* Persistent reservation manager abstract class
*
* Copyright (c) 2017 Red Hat, Inc.
*
* Author: Paolo Bonzini <pbonzini@redhat.com>
*
* This code is licensed under the LGPL.
*
*/
#include "qemu/osdep.h"
#include <scsi/sg.h>
#include "qapi/error.h"
#include "block/aio.h"
#include "block/thread-pool.h"
#include "scsi/pr-manager.h"
#include "trace.h"
typedef struct PRManagerData {
PRManager *pr_mgr;
struct sg_io_hdr *hdr;
int fd;
} PRManagerData;
static int pr_manager_worker(void *opaque)
{
PRManagerData *data = opaque;
PRManager *pr_mgr = data->pr_mgr;
PRManagerClass *pr_mgr_class =
PR_MANAGER_GET_CLASS(pr_mgr);
struct sg_io_hdr *hdr = data->hdr;
int fd = data->fd;
int r;
g_free(data);
trace_pr_manager_run(fd, hdr->cmdp[0], hdr->cmdp[1]);
/* The reference was taken in pr_manager_execute. */
r = pr_mgr_class->run(pr_mgr, fd, hdr);
object_unref(OBJECT(pr_mgr));
return r;
}
BlockAIOCB *pr_manager_execute(PRManager *pr_mgr,
AioContext *ctx, int fd,
struct sg_io_hdr *hdr,
BlockCompletionFunc *complete,
void *opaque)
{
PRManagerData *data = g_new(PRManagerData, 1);
ThreadPool *pool = aio_get_thread_pool(ctx);
trace_pr_manager_execute(fd, hdr->cmdp[0], hdr->cmdp[1], opaque);
data->pr_mgr = pr_mgr;
data->fd = fd;
data->hdr = hdr;
/* The matching object_unref is in pr_manager_worker. */
object_ref(OBJECT(pr_mgr));
return thread_pool_submit_aio(pool, pr_manager_worker,
data, complete, opaque);
}
static const TypeInfo pr_manager_info = {
.parent = TYPE_OBJECT,
.name = TYPE_PR_MANAGER,
.class_size = sizeof(PRManagerClass),
.abstract = true,
.interfaces = (InterfaceInfo[]) {
{ TYPE_USER_CREATABLE },
{ }
}
};
PRManager *pr_manager_lookup(const char *id, Error **errp)
{
Object *obj;
PRManager *pr_mgr;
obj = object_resolve_path_component(object_get_objects_root(), id);
if (!obj) {
error_setg(errp, "No persistent reservation manager with id '%s'", id);
return NULL;
}
pr_mgr = (PRManager *)
object_dynamic_cast(obj,
TYPE_PR_MANAGER);
if (!pr_mgr) {
error_setg(errp,
"Object with id '%s' is not a persistent reservation manager",
id);
return NULL;
}
return pr_mgr;
}
static void
pr_manager_register_types(void)
{
type_register_static(&pr_manager_info);
}
type_init(pr_manager_register_types);