From: Paolo Bonzini <pbonzini@redhat.com>

Date: Tue, 22 Aug 2017 06:50:18 +0200

Subject: [PATCH] scsi: build qemu-pr-helper

Introduce a privileged helper to run persistent reservation commands.

This lets virtual machines send persistent reservations without using

CAP_SYS_RAWIO or out-of-tree patches.  The helper uses Unix permissions

and SCM_RIGHTS to restrict access to processes that can access its socket

and prove that they have an open file descriptor for a raw SCSI device.

The next patch will also correct the usage of persistent reservations

with multipath devices.

It would also be possible to support for Linux's IOC_PR_* ioctls in

the future, to support NVMe devices.  For now, however, only SCSI is

supported.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

---

 Makefile                   |   4 +-

 configure                  |  14 +-

 docs/interop/pr-helper.rst |  83 +++++

 docs/pr-manager.rst        |  33 ++

 scsi/pr-helper.h           |  41 +++

 scsi/qemu-pr-helper.c      | 735 +++++++++++++++++++++++++++++++++++++++++++++

 6 files changed, 905 insertions(+), 5 deletions(-)

 create mode 100644 docs/interop/pr-helper.rst

 create mode 100644 scsi/pr-helper.h

 create mode 100644 scsi/qemu-pr-helper.c

diff --git a/Makefile b/Makefile

index 81447b1f08..f07c0d7e9c 100644

--- a/Makefile

+++ b/Makefile

@@ -382,6 +382,8 @@ qemu-bridge-helper$(EXESUF): qemu-bridge-helper.o $(COMMON_LDADDS)

 fsdev/virtfs-proxy-helper$(EXESUF): fsdev/virtfs-proxy-helper.o fsdev/9p-marshal.o fsdev/9p-iov-marshal.o $(COMMON_LDADDS)

 fsdev/virtfs-proxy-helper$(EXESUF): LIBS += -lcap

+scsi/qemu-pr-helper$(EXESUF): scsi/qemu-pr-helper.o scsi/utils.o $(crypto-obj-y) $(io-obj-y) $(qom-obj-y) $(COMMON_LDADDS)

+

 qemu-img-cmds.h: $(SRC_PATH)/qemu-img-cmds.hx $(SRC_PATH)/scripts/hxtool

 	$(call quiet-command,sh $(SRC_PATH)/scripts/hxtool -h < $< > $@,"GEN","$@")

@@ -489,7 +491,7 @@ clean:

 	rm -f *.msi

 	find . \( -name '*.so' -o -name '*.dll' -o -name '*.mo' -o -name '*.[oda]' \) -type f -exec rm {} +

 	rm -f $(filter-out %.tlb,$(TOOLS)) $(HELPERS-y) qemu-ga TAGS cscope.* *.pod *~ */*~

-	rm -f fsdev/*.pod

+	rm -f fsdev/*.pod scsi/*.pod

 	rm -f qemu-img-cmds.h

 	rm -f ui/shader/*-vert.h ui/shader/*-frag.h

 	@# May not be present in GENERATED_FILES

diff --git a/configure b/configure

index dd73cce62f..14bdf9bb31 100755

--- a/configure

+++ b/configure

@@ -5070,16 +5070,22 @@ if test "$want_tools" = "yes" ; then

   fi

 fi

 if test "$softmmu" = yes ; then

-  if test "$virtfs" != no ; then

-    if test "$cap" = yes && test "$linux" = yes && test "$attr" = yes ; then

+  if test "$linux" = yes; then

+    if test "$virtfs" != no && test "$cap" = yes && test "$attr" = yes ; then

       virtfs=yes

       tools="$tools fsdev/virtfs-proxy-helper\$(EXESUF)"

     else

       if test "$virtfs" = yes; then

-        error_exit "VirtFS is supported only on Linux and requires libcap devel and libattr devel"

+        error_exit "VirtFS requires libcap devel and libattr devel"

       fi

       virtfs=no

     fi

+    tools="$tools scsi/qemu-pr-helper\$(EXESUF)"

+  else

+    if test "$virtfs" = yes; then

+      error_exit "VirtFS is supported only on Linux"

+    fi

+    virtfs=no

   fi

 fi

@@ -6545,7 +6551,7 @@ fi

 # build tree in object directory in case the source is not in the current directory

 DIRS="tests tests/tcg tests/tcg/cris tests/tcg/lm32 tests/libqos tests/qapi-schema tests/tcg/xtensa tests/qemu-iotests"

-DIRS="$DIRS docs docs/interop fsdev"

+DIRS="$DIRS docs docs/interop fsdev scsi"

 DIRS="$DIRS pc-bios/optionrom pc-bios/spapr-rtas pc-bios/s390-ccw"

 DIRS="$DIRS roms/seabios roms/vgabios"

 DIRS="$DIRS qapi-generated"

diff --git a/docs/interop/pr-helper.rst b/docs/interop/pr-helper.rst

new file mode 100644

index 0000000000..9f76d5bcf9

--- /dev/null

+++ b/docs/interop/pr-helper.rst

@@ -0,0 +1,83 @@

+..

+

+======================================

+Persistent reservation helper protocol

+======================================

+

+QEMU's SCSI passthrough devices, ``scsi-block`` and ``scsi-generic``,

+can delegate implementation of persistent reservations to an external

+(and typically privileged) program.  Persistent Reservations allow

+restricting access to block devices to specific initiators in a shared

+storage setup.

+

+For a more detailed reference please refer the the SCSI Primary

+Commands standard, specifically the section on Reservations and the

+"PERSISTENT RESERVE IN" and "PERSISTENT RESERVE OUT" commands.

+

+This document describes the socket protocol used between QEMU's

+``pr-manager-helper`` object and the external program.

+

+.. contents::

+

+Connection and initialization

+-----------------------------

+

+All data transmitted on the socket is big-endian.

+

+After connecting to the helper program's socket, the helper starts a simple

+feature negotiation process by writing four bytes corresponding to

+the features it exposes (``supported_features``).  QEMU reads it,

+then writes four bytes corresponding to the desired features of the

+helper program (``requested_features``).

+

+If a bit is 1 in ``requested_features`` and 0 in ``supported_features``,

+the corresponding feature is not supported by the helper and the connection

+is closed.  On the other hand, it is acceptable for a bit to be 0 in

+``requested_features`` and 1 in ``supported_features``; in this case,

+the helper will not enable the feature.

+

+Right now no feature is defined, so the two parties always write four

+zero bytes.

+

+Command format

+--------------

+

+It is invalid to send multiple commands concurrently on the same

+socket.  It is however possible to connect multiple sockets to the

+helper and send multiple commands to the helper for one or more

+file descriptors.

+

+A command consists of a request and a response.  A request consists

+of a 16-byte SCSI CDB.  A file descriptor must be passed to the helper

+together with the SCSI CDB using ancillary data.

+

+The CDB has the following limitations:

+

+- the command (stored in the first byte) must be one of 0x5E

+  (PERSISTENT RESERVE IN) or 0x5F (PERSISTENT RESERVE OUT).

+

+- the allocation length (stored in bytes 7-8 of the CDB for PERSISTENT

+  RESERVE IN) or parameter list length (stored in bytes 5-8 of the CDB

+  for PERSISTENT RESERVE OUT) is limited to 8 KiB.

+

+For PERSISTENT RESERVE OUT, the parameter list is sent right after the

+CDB.  The length of the parameter list is taken from the CDB itself.

+

+The helper's reply has the following structure:

+

+- 4 bytes for the SCSI status

+

+- 4 bytes for the payload size (nonzero only for PERSISTENT RESERVE IN

+  and only if the SCSI status is 0x00, i.e. GOOD)

+

+- 96 bytes for the SCSI sense data

+

+- if the size is nonzero, the payload follows

+

+The sense data is always sent to keep the protocol simple, even though

+it is only valid if the SCSI status is CHECK CONDITION (0x02).

+

+The payload size is always less than or equal to the allocation length

+specified in the CDB for the PERSISTENT RESERVE IN command.

+

+If the protocol is violated, the helper closes the socket.

diff --git a/docs/pr-manager.rst b/docs/pr-manager.rst

index b6089fb57c..7107e59fb8 100644

--- a/docs/pr-manager.rst

+++ b/docs/pr-manager.rst

@@ -49,3 +49,36 @@ Alternatively, using ``-blockdev``::

           -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

+

+----------------------------------

+Invoking :program:`qemu-pr-helper`

+----------------------------------

+

+QEMU provides an implementation of the persistent reservation helper,

+called :program:`qemu-pr-helper`.  The helper should be started as a

+system service and supports the following option:

+

+-d, --daemon              run in the background

+-q, --quiet               decrease verbosity

+-f, --pidfile=path        PID file when running as a daemon

+-k, --socket=path         path to the socket

+-T, --trace=trace-opts    tracing options

+

+By default, the socket and PID file are placed in the runtime state

+directory, for example :file:`/var/run/qemu-pr-helper.sock` and

+:file:`/var/run/qemu-pr-helper.pid`.  The PID file is not created

+unless :option:`-d` is passed too.

+

+:program:`qemu-pr-helper` can also use the systemd socket activation

+protocol.  In this case, the systemd socket unit should specify a

+Unix stream socket, like this::

+

+    [Socket]

+    ListenStream=/var/run/qemu-pr-helper.sock

+

+After connecting to the socket, :program:`qemu-pr-helper`` can optionally drop

+root privileges, except for those capabilities that are needed for

+its operation.  To do this, add the following options:

+

+-u, --user=user           user to drop privileges to

+-g, --group=group         group to drop privileges to

diff --git a/scsi/pr-helper.h b/scsi/pr-helper.h

new file mode 100644

index 0000000000..96c50a9e5f

--- /dev/null

+++ b/scsi/pr-helper.h

@@ -0,0 +1,41 @@

+/* Definitions for QEMU's persistent reservation helper daemon

+ *

+ * Copyright (C) 2017 Red Hat, Inc.

+ *

+ * Author:

+ *   Paolo Bonzini <pbonzini@redhat.com>

+ *

+ * Permission is hereby granted, free of charge, to any person obtaining a copy

+ * of this software and associated documentation files (the "Software"), to

+ * deal in the Software without restriction, including without limitation the

+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or

+ * sell copies of the Software, and to permit persons to whom the Software is

+ * furnished to do so, subject to the following conditions:

+ *

+ * The above copyright notice and this permission notice shall be included in

+ * all copies or substantial portions of the Software.

+ *

+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS

+ * IN THE SOFTWARE.

+ */

+#ifndef QEMU_PR_HELPER_H

+#define QEMU_PR_HELPER_H 1

+

+#include <stdint.h>

+

+#define PR_HELPER_CDB_SIZE     16

+#define PR_HELPER_SENSE_SIZE   96

+#define PR_HELPER_DATA_SIZE    8192

+

+typedef struct PRHelperResponse {

+    int32_t result;

+    int32_t sz;

+    uint8_t sense[PR_HELPER_SENSE_SIZE];

+} PRHelperResponse;

+

+#endif

diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c

new file mode 100644

index 0000000000..e39efbd529

--- /dev/null

+++ b/scsi/qemu-pr-helper.c

@@ -0,0 +1,735 @@

+/*

+ * Privileged helper to handle persistent reservation commands for QEMU

+ *

+ * Copyright (C) 2017 Red Hat, Inc. <pbonzini@redhat.com>

+ *

+ * Author: Paolo Bonzini <pbonzini@redhat.com>

+ *

+ * This program is free software; you can redistribute it and/or modify

+ * it under the terms of the GNU General Public License as published by

+ * the Free Software Foundation; under version 2 of the License.

+ *

+ * This program is distributed in the hope that it will be useful,

+ * but WITHOUT ANY WARRANTY; without even the implied warranty of

+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

+ * GNU General Public License for more details.

+ *

+ * You should have received a copy of the GNU General Public License

+ * along with this program; if not, see <http://www.gnu.org/licenses/>.

+ */

+

+#include "qemu/osdep.h"

+#include <getopt.h>

+#include <sys/ioctl.h>

+#include <linux/dm-ioctl.h>

+#include <scsi/sg.h>

+

+#ifdef CONFIG_LIBCAP

+#include <cap-ng.h>

+#endif

+#include <pwd.h>

+#include <grp.h>

+

+#include "qapi/error.h"

+#include "qemu-common.h"

+#include "qemu/cutils.h"

+#include "qemu/main-loop.h"

+#include "qemu/error-report.h"

+#include "qemu/config-file.h"

+#include "qemu/bswap.h"

+#include "qemu/log.h"

+#include "qemu/systemd.h"

+#include "qapi/util.h"

+#include "qapi/qmp/qstring.h"

+#include "io/channel-socket.h"

+#include "trace/control.h"

+#include "qemu-version.h"

+

+#include "block/aio.h"

+#include "block/thread-pool.h"

+

+#include "scsi/constants.h"

+#include "scsi/utils.h"

+#include "pr-helper.h"

+

+#define PR_OUT_FIXED_PARAM_SIZE 24

+

+static char *socket_path;

+static char *pidfile;

+static enum { RUNNING, TERMINATE, TERMINATING } state;

+static QIOChannelSocket *server_ioc;

+static int server_watch;

+static int num_active_sockets = 1;

+static int verbose;

+

+#ifdef CONFIG_LIBCAP

+static int uid = -1;

+static int gid = -1;

+#endif

+

+static void usage(const char *name)

+{

+    (printf) (

+"Usage: %s [OPTIONS] FILE\n"

+"Persistent Reservation helper program for QEMU\n"

+"\n"

+"  -h, --help                display this help and exit\n"

+"  -V, --version             output version information and exit\n"

+"\n"

+"  -d, --daemon              run in the background\n"

+"  -f, --pidfile=PATH        PID file when running as a daemon\n"

+"                            (default '%s')\n"

+"  -k, --socket=PATH         path to the unix socket\n"

+"                            (default '%s')\n"

+"  -T, --trace [[enable=]<pattern>][,events=<file>][,file=<file>]\n"

+"                            specify tracing options\n"

+#ifdef CONFIG_LIBCAP

+"  -u, --user=USER           user to drop privileges to\n"

+"  -g, --group=GROUP         group to drop privileges to\n"

+#endif

+"\n"

+QEMU_HELP_BOTTOM "\n"

+    , name, pidfile, socket_path);

+}

+

+static void version(const char *name)

+{

+    printf(

+"%s " QEMU_VERSION QEMU_PKGVERSION "\n"

+"Written by Paolo Bonzini.\n"

+"\n"

+QEMU_COPYRIGHT "\n"

+"This is free software; see the source for copying conditions.  There is NO\n"

+"warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n"

+    , name);

+}

+

+static void write_pidfile(void)

+{

+    int pidfd;

+    char pidstr[32];

+

+    pidfd = qemu_open(pidfile, O_CREAT|O_WRONLY, S_IRUSR|S_IWUSR);

+    if (pidfd == -1) {

+        error_report("Cannot open pid file, %s", strerror(errno));

+        exit(EXIT_FAILURE);

+    }

+

+    if (lockf(pidfd, F_TLOCK, 0)) {

+        error_report("Cannot lock pid file, %s", strerror(errno));

+        goto fail;

+    }

+    if (ftruncate(pidfd, 0)) {

+        error_report("Failed to truncate pid file");

+        goto fail;

+    }

+

+    snprintf(pidstr, sizeof(pidstr), "%d\n", getpid());

+    if (write(pidfd, pidstr, strlen(pidstr)) != strlen(pidstr)) {

+        error_report("Failed to write pid file");

+        goto fail;

+    }

+    return;

+

+fail:

+    unlink(pidfile);

+    close(pidfd);

+    exit(EXIT_FAILURE);

+}

+

+/* SG_IO support */

+

+typedef struct PRHelperSGIOData {

+    int fd;

+    const uint8_t *cdb;

+    uint8_t *sense;

+    uint8_t *buf;

+    int sz;              /* input/output */

+    int dir;

+} PRHelperSGIOData;

+

+static int do_sgio_worker(void *opaque)

+{

+    PRHelperSGIOData *data = opaque;

+    struct sg_io_hdr io_hdr;

+    int ret;

+    int status;

+    SCSISense sense_code;

+

+    memset(data->sense, 0, PR_HELPER_SENSE_SIZE);

+    memset(&io_hdr, 0, sizeof(io_hdr));

+    io_hdr.interface_id = 'S';

+    io_hdr.cmd_len = PR_HELPER_CDB_SIZE;

+    io_hdr.cmdp = (uint8_t *)data->cdb;

+    io_hdr.sbp = data->sense;

+    io_hdr.mx_sb_len = PR_HELPER_SENSE_SIZE;

+    io_hdr.timeout = 1;

+    io_hdr.dxfer_direction = data->dir;

+    io_hdr.dxferp = (char *)data->buf;

+    io_hdr.dxfer_len = data->sz;

+    ret = ioctl(data->fd, SG_IO, &io_hdr);

+    status = sg_io_sense_from_errno(ret < 0 ? errno : 0, &io_hdr,

+                                    &sense_code);

+    if (status == GOOD) {

+        data->sz -= io_hdr.resid;

+    } else {

+        data->sz = 0;

+    }

+

+    if (status == CHECK_CONDITION &&

+        !(io_hdr.driver_status & SG_ERR_DRIVER_SENSE)) {

+        scsi_build_sense(data->sense, sense_code);

+    }

+

+    return status;

+}

+

+static int do_sgio(int fd, const uint8_t *cdb, uint8_t *sense,

+                    uint8_t *buf, int *sz, int dir)

+{

+    ThreadPool *pool = aio_get_thread_pool(qemu_get_aio_context());

+    int r;

+

+    PRHelperSGIOData data = {

+        .fd = fd,

+        .cdb = cdb,

+        .sense = sense,

+        .buf = buf,

+        .sz = *sz,

+        .dir = dir,

+    };

+

+    r = thread_pool_submit_co(pool, do_sgio_worker, &data);

+    *sz = data.sz;

+    return r;

+}

+

+static int do_pr_in(int fd, const uint8_t *cdb, uint8_t *sense,

+                    uint8_t *data, int *resp_sz)

+{

+    return do_sgio(fd, cdb, sense, data, resp_sz,

+                   SG_DXFER_FROM_DEV);

+}

+

+static int do_pr_out(int fd, const uint8_t *cdb, uint8_t *sense,

+                     const uint8_t *param, int sz)

+{

+    int resp_sz = sz;

+    return do_sgio(fd, cdb, sense, (uint8_t *)param, &resp_sz,

+                   SG_DXFER_TO_DEV);

+}

+

+/* Client */

+

+typedef struct PRHelperClient {

+    QIOChannelSocket *ioc;

+    Coroutine *co;

+    int fd;

+    uint8_t data[PR_HELPER_DATA_SIZE];

+} PRHelperClient;

+

+typedef struct PRHelperRequest {

+    int fd;

+    size_t sz;

+    uint8_t cdb[PR_HELPER_CDB_SIZE];

+} PRHelperRequest;

+

+static int coroutine_fn prh_read(PRHelperClient *client, void *buf, int sz,

+                                 Error **errp)

+{

+    int ret = 0;

+

+    while (sz > 0) {

+        int *fds = NULL;

+        size_t nfds = 0;

+        int i;

+        struct iovec iov;

+        ssize_t n_read;

+

+        iov.iov_base = buf;

+        iov.iov_len = sz;

+        n_read = qio_channel_readv_full(QIO_CHANNEL(client->ioc), &iov, 1,

+                                        &fds, &nfds, errp);

+

+        if (n_read == QIO_CHANNEL_ERR_BLOCK) {

+            qio_channel_yield(QIO_CHANNEL(client->ioc), G_IO_IN);

+            continue;

+        }

+        if (n_read <= 0) {

+            ret = n_read ? n_read : -1;

+            goto err;

+        }

+

+        /* Stash one file descriptor per request.  */

+        if (nfds) {

+            bool too_many = false;

+            for (i = 0; i < nfds; i++) {

+                if (client->fd == -1) {

+                    client->fd = fds[i];

+                } else {

+                    close(fds[i]);

+                    too_many = true;

+                }

+            }

+            g_free(fds);

+            if (too_many) {

+                ret = -1;

+                goto err;

+            }

+        }

+

+        buf += n_read;

+        sz -= n_read;

+    }

+

+    return 0;

+

+err:

+    if (client->fd != -1) {

+        close(client->fd);

+        client->fd = -1;

+    }

+    return ret;

+}

+

+static int coroutine_fn prh_read_request(PRHelperClient *client,

+                                         PRHelperRequest *req,

+                                         PRHelperResponse *resp, Error **errp)

+{

+    uint32_t sz;

+

+    if (prh_read(client, req->cdb, sizeof(req->cdb), NULL) < 0) {

+        return -1;

+    }

+

+    if (client->fd == -1) {

+        error_setg(errp, "No file descriptor in request.");

+        return -1;

+    }

+

+    if (req->cdb[0] != PERSISTENT_RESERVE_OUT &&

+        req->cdb[0] != PERSISTENT_RESERVE_IN) {

+        error_setg(errp, "Invalid CDB, closing socket.");

+        goto out_close;

+    }

+

+    sz = scsi_cdb_xfer(req->cdb);

+    if (sz > sizeof(client->data)) {

+        goto out_close;

+    }

+

+    if (req->cdb[0] == PERSISTENT_RESERVE_OUT) {

+        if (qio_channel_read_all(QIO_CHANNEL(client->ioc),

+                                 (char *)client->data, sz,

+                                 errp) < 0) {

+            goto out_close;

+        }

+        if ((fcntl(client->fd, F_GETFL) & O_ACCMODE) == O_RDONLY) {

+            scsi_build_sense(resp->sense, SENSE_CODE(INVALID_OPCODE));

+            sz = 0;

+        } else if (sz < PR_OUT_FIXED_PARAM_SIZE) {

+            /* Illegal request, Parameter list length error.  This isn't fatal;

+             * we have read the data, send an error without closing the socket.

+             */

+            scsi_build_sense(resp->sense, SENSE_CODE(INVALID_PARAM_LEN));

+            sz = 0;

+        }

+        if (sz == 0) {

+            resp->result = CHECK_CONDITION;

+            close(client->fd);

+            client->fd = -1;

+        }

+    }

+

+    req->fd = client->fd;

+    req->sz = sz;

+    client->fd = -1;

+    return sz;

+

+out_close:

+    close(client->fd);

+    client->fd = -1;

+    return -1;

+}

+

+static int coroutine_fn prh_write_response(PRHelperClient *client,

+                                           PRHelperRequest *req,

+                                           PRHelperResponse *resp, Error **errp)

+{

+    ssize_t r;

+    size_t sz;

+

+    if (req->cdb[0] == PERSISTENT_RESERVE_IN && resp->result == GOOD) {

+        assert(resp->sz <= req->sz && resp->sz <= sizeof(client->data));

+    } else {

+        assert(resp->sz == 0);

+    }

+

+    sz = resp->sz;

+

+    resp->result = cpu_to_be32(resp->result);

+    resp->sz = cpu_to_be32(resp->sz);

+    r = qio_channel_write_all(QIO_CHANNEL(client->ioc),

+                              (char *) resp, sizeof(*resp), errp);

+    if (r < 0) {

+        return r;

+    }

+

+    r = qio_channel_write_all(QIO_CHANNEL(client->ioc),

+                              (char *) client->data,

+                              sz, errp);

+    return r < 0 ? r : 0;

+}

+

+static void coroutine_fn prh_co_entry(void *opaque)

+{

+    PRHelperClient *client = opaque;

+    Error *local_err = NULL;

+    uint32_t flags;

+    int r;

+

+    qio_channel_set_blocking(QIO_CHANNEL(client->ioc),

+                             false, NULL);

+    qio_channel_attach_aio_context(QIO_CHANNEL(client->ioc),

+                                   qemu_get_aio_context());

+

+    /* A very simple negotiation for future extensibility.  No features

+     * are defined so write 0.

+     */

+    flags = cpu_to_be32(0);

+    r = qio_channel_write_all(QIO_CHANNEL(client->ioc),

+                             (char *) &flags, sizeof(flags), NULL);

+    if (r < 0) {

+        goto out;

+    }

+

+    r = qio_channel_read_all(QIO_CHANNEL(client->ioc),

+                             (char *) &flags, sizeof(flags), NULL);

+    if (be32_to_cpu(flags) != 0 || r < 0) {

+        goto out;

+    }

+

+    while (atomic_read(&state) == RUNNING) {

+        PRHelperRequest req;

+        PRHelperResponse resp;

+        int sz;

+

+        sz = prh_read_request(client, &req, &resp, &local_err);

+        if (sz < 0) {

+            break;

+        }

+

+        if (sz > 0) {

+            num_active_sockets++;

+            if (req.cdb[0] == PERSISTENT_RESERVE_OUT) {

+                r = do_pr_out(req.fd, req.cdb, resp.sense,

+                              client->data, sz);

+                resp.sz = 0;

+            } else {

+                resp.sz = sizeof(client->data);

+                r = do_pr_in(req.fd, req.cdb, resp.sense,

+                             client->data, &resp.sz);

+                resp.sz = MIN(resp.sz, sz);

+            }

+            num_active_sockets--;

+            close(req.fd);

+            if (r == -1) {

+                break;

+            }

+            resp.result = r;

+        }

+

+        if (prh_write_response(client, &req, &resp, &local_err) < 0) {