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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>
109 lines
2.6 KiB
C
109 lines
2.6 KiB
C
/*
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* Persistent reservation manager abstract class
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*
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* Copyright (c) 2017 Red Hat, Inc.
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This code is licensed under the LGPL.
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*
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*/
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#include "qemu/osdep.h"
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#include <scsi/sg.h>
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#include "qapi/error.h"
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#include "block/aio.h"
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#include "block/thread-pool.h"
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#include "scsi/pr-manager.h"
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#include "trace.h"
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typedef struct PRManagerData {
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PRManager *pr_mgr;
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struct sg_io_hdr *hdr;
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int fd;
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} PRManagerData;
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static int pr_manager_worker(void *opaque)
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{
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PRManagerData *data = opaque;
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PRManager *pr_mgr = data->pr_mgr;
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PRManagerClass *pr_mgr_class =
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PR_MANAGER_GET_CLASS(pr_mgr);
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struct sg_io_hdr *hdr = data->hdr;
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int fd = data->fd;
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int r;
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g_free(data);
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trace_pr_manager_run(fd, hdr->cmdp[0], hdr->cmdp[1]);
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/* The reference was taken in pr_manager_execute. */
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r = pr_mgr_class->run(pr_mgr, fd, hdr);
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object_unref(OBJECT(pr_mgr));
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return r;
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}
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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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{
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PRManagerData *data = g_new(PRManagerData, 1);
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ThreadPool *pool = aio_get_thread_pool(ctx);
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trace_pr_manager_execute(fd, hdr->cmdp[0], hdr->cmdp[1], opaque);
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data->pr_mgr = pr_mgr;
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data->fd = fd;
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data->hdr = hdr;
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/* The matching object_unref is in pr_manager_worker. */
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object_ref(OBJECT(pr_mgr));
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return thread_pool_submit_aio(pool, pr_manager_worker,
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data, complete, opaque);
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}
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static const TypeInfo pr_manager_info = {
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.parent = TYPE_OBJECT,
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.name = TYPE_PR_MANAGER,
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.class_size = sizeof(PRManagerClass),
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.abstract = true,
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.interfaces = (InterfaceInfo[]) {
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{ TYPE_USER_CREATABLE },
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{ }
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}
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};
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PRManager *pr_manager_lookup(const char *id, Error **errp)
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{
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Object *obj;
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PRManager *pr_mgr;
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obj = object_resolve_path_component(object_get_objects_root(), id);
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if (!obj) {
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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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pr_mgr = (PRManager *)
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object_dynamic_cast(obj,
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TYPE_PR_MANAGER);
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if (!pr_mgr) {
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error_setg(errp,
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"Object with id '%s' is not a persistent reservation manager",
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id);
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return NULL;
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}
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return pr_mgr;
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}
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static void
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pr_manager_register_types(void)
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{
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type_register_static(&pr_manager_info);
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}
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type_init(pr_manager_register_types);
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