diff mbox

[v2,RFC] block/vxhs: Initial commit to add Veritas HyperScale VxHS block device support

Message ID 1470621661-21877-1-git-send-email-ashish.mittal@veritas.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ashish Mittal Aug. 8, 2016, 2:01 a.m. UTC
This patch adds support for a new block device type called "vxhs".
Source code for the library that this code loads can be downloaded from:
https://github.com/MittalAshish/libqnio.git

Version 2 patch submission fixes the following issues:
(1) Removed code to dlopen library. We now check if libqnio is installed during
    configure, and directly link with it.
(2) Changed file headers to mention GPLv2-or-later license.
(3) Removed unnecessary type casts and inlines.
(4) Removed custom tokenize function and modified code to use g_strsplit.
(5) Replaced malloc/free with g_new/g_free and removed code that checks for
    memory allocation failure conditions.
(6) Removed some block ops implementations that were place-holders only.
(7) Removed all custom debug messages. Added new messages in block/trace-events
(8) Other miscellaneous corrections.

TODO: QAPI changes and (fixes to) review comments from Stefan.
Signed-off-by: Ashish Mittal <ashish.mittal@veritas.com>
---
 block/Makefile.objs |    2 +
 block/trace-events  |   40 ++
 block/vxhs.c        | 1199 +++++++++++++++++++++++++++++++++++++++++++++++++++
 block/vxhs.h        |  294 +++++++++++++
 configure           |   50 +++
 5 files changed, 1585 insertions(+)
 create mode 100644 block/vxhs.c
 create mode 100644 block/vxhs.h

Comments

Daniel P. Berrangé Aug. 8, 2016, 9:10 a.m. UTC | #1
On Sun, Aug 07, 2016 at 07:01:01PM -0700, Ashish Mittal wrote:
> This patch adds support for a new block device type called "vxhs".

I'd suggest this commit message should include an example of the
syntax for using this on the CLI

> Source code for the library that this code loads can be downloaded from:
> https://github.com/MittalAshish/libqnio.git
> 
> Version 2 patch submission fixes the following issues:
> (1) Removed code to dlopen library. We now check if libqnio is installed during
>     configure, and directly link with it.
> (2) Changed file headers to mention GPLv2-or-later license.
> (3) Removed unnecessary type casts and inlines.
> (4) Removed custom tokenize function and modified code to use g_strsplit.
> (5) Replaced malloc/free with g_new/g_free and removed code that checks for
>     memory allocation failure conditions.
> (6) Removed some block ops implementations that were place-holders only.
> (7) Removed all custom debug messages. Added new messages in block/trace-events
> (8) Other miscellaneous corrections.

FYI, if you put notes about what changed in between postings below the
'---' line, then with your patch is applied, git is intelligent enough
to drop these notes.

> 
> TODO: QAPI changes and (fixes to) review comments from Stefan.
> Signed-off-by: Ashish Mittal <ashish.mittal@veritas.com>
> ---

eg, put your 'Changed in v2' stuff just here.

>  block/Makefile.objs |    2 +
>  block/trace-events  |   40 ++
>  block/vxhs.c        | 1199 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  block/vxhs.h        |  294 +++++++++++++
>  configure           |   50 +++
>  5 files changed, 1585 insertions(+)
>  create mode 100644 block/vxhs.c
>  create mode 100644 block/vxhs.h
> 


> diff --git a/block/vxhs.c b/block/vxhs.c
> new file mode 100644
> index 0000000..9a82757
> --- /dev/null
> +++ b/block/vxhs.c
> @@ -0,0 +1,1199 @@
> +/*
> + * QEMU Block driver for Veritas HyperScale (VxHS)
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "vxhs.h"
> +#include <qnio/qnio_api.h>
> +#include "trace.h"
> +
> +/* qnio client ioapi_ctx */
> +static void __attribute__((unused)) *global_qnio_ctx;
> +
> +/* insure init once */
> +static pthread_mutex_t __attribute__((unused))  of_global_ctx_lock =
> +    PTHREAD_MUTEX_INITIALIZER;

Not sure why you're adding attribute__(unused) here, since both these
vars are clearly used.

BTW, since we're using glib, you should use  G_GNUC_UNUSD as the
annotation, but since these vars are used, just drop the annotation
entirely.

> +
> +/* HyperScale Driver Version */
> +static const int __attribute__((unused)) vxhs_drv_version = 8895;

This only seems to be used in a single trace() message, so can probably
be just deleted entirely


> diff --git a/configure b/configure
> index f57fcc6..c4f6261 100755
> --- a/configure
> +++ b/configure
> @@ -320,6 +320,7 @@ vhdx=""
>  numa=""
>  tcmalloc="no"
>  jemalloc="no"
> +vxhs="yes"
>  
>  # parse CC options first
>  for opt do
> @@ -1150,6 +1151,11 @@ for opt do
>    ;;
>    --enable-jemalloc) jemalloc="yes"
>    ;;
> +  --disable-vxhs) vxhs="no"
> +  ;;
> +  --enable-vxhs) vxhs="yes"
> +  ;;
> +
>    *)
>        echo "ERROR: unknown option $opt"
>        echo "Try '$0 --help' for more information"
> @@ -1380,6 +1386,7 @@ disabled with --disable-FEATURE, default is enabled if available:
>    numa            libnuma support
>    tcmalloc        tcmalloc support
>    jemalloc        jemalloc support
> +  vxhs            Veritas HyperScale vDisk backend support
>  
>  NOTE: The object files are built at the place where configure is launched
>  EOF
> @@ -4543,6 +4550,43 @@ if do_cc -nostdlib -Wl,-r -Wl,--no-relax -o $TMPMO $TMPO; then
>  fi
>  
>  ##########################################
> +# Veritas HyperScale block driver VxHS
> +# Check if libqnio is installed
> +if test "$vxhs" != "no" ; then
> +  cat > $TMPC <<EOF
> +#include <stdio.h>
> +#include <qnio/qnio_api.h>
> +
> +void vxhs_inc_acb_segment_count(void *acb, int count);
> +void vxhs_dec_acb_segment_count(void *acb, int count);
> +void vxhs_set_acb_buffer(void *ptr, void *buffer);
> +
> +void vxhs_inc_acb_segment_count(void *ptr, int count)
> +{
> +}
> +void vxhs_dec_acb_segment_count(void *ptr, int count)
> +{
> +}
> +void vxhs_set_acb_buffer(void *ptr, void *buffer)
> +{
> +}
> +int main(void) {
> +    qemu_ck_initialize_lock();
> +    return 0;
> +}
> +EOF
> +  vxhs_libs="-lqnioshim -lqnio"
> +  if compile_prog "" "$vxhs_libs" ; then
> +    vxhs=yes
> +  else
> +    if test "$vxhs" = "yes" ; then
> +      feature_not_found "vxhs block device" "Install libqnio. See github"
> +    fi
> +    vxhs=no
> +  fi
> +fi

There's nothing wrong with this code, but it occurs to me that
since libqnio is a completely new library you've written yourself,
it would be nice if you could add a pkg-config file to the libqio
install. That would allow QEMU to detect libqnio using the standard
pkg-config mechanism that most libraries uses these days.



Regards,
Daniel
Stefan Hajnoczi Aug. 10, 2016, 2:32 p.m. UTC | #2
On Sun, Aug 07, 2016 at 07:01:01PM -0700, Ashish Mittal wrote:
> This patch adds support for a new block device type called "vxhs".
> Source code for the library that this code loads can be downloaded from:
> https://github.com/MittalAshish/libqnio.git
> 
> Version 2 patch submission fixes the following issues:
> (1) Removed code to dlopen library. We now check if libqnio is installed during
>     configure, and directly link with it.
> (2) Changed file headers to mention GPLv2-or-later license.
> (3) Removed unnecessary type casts and inlines.
> (4) Removed custom tokenize function and modified code to use g_strsplit.
> (5) Replaced malloc/free with g_new/g_free and removed code that checks for
>     memory allocation failure conditions.
> (6) Removed some block ops implementations that were place-holders only.
> (7) Removed all custom debug messages. Added new messages in block/trace-events
> (8) Other miscellaneous corrections.
> 
> TODO: QAPI changes and (fixes to) review comments from Stefan.
> Signed-off-by: Ashish Mittal <ashish.mittal@veritas.com>
> ---
>  block/Makefile.objs |    2 +
>  block/trace-events  |   40 ++
>  block/vxhs.c        | 1199 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  block/vxhs.h        |  294 +++++++++++++
>  configure           |   50 +++
>  5 files changed, 1585 insertions(+)
>  create mode 100644 block/vxhs.c
>  create mode 100644 block/vxhs.h

I'll review v3 with the issues I raised addressed.

Please put the patch changelog below the '---' line.  This way the
changelog is not included in the git history when the patch is merged.
The changelog is only useful while the patch is being discussed on the
mailing list but shouldn't be included in the git-log(1) output.
Typically it looks like this:

---
v2:
 * Removed code to dlopen library. We now check if libqnio is installed
   during configure, and directly link with it.
 ...
Kevin Wolf Aug. 11, 2016, 3 p.m. UTC | #3
Am 08.08.2016 um 04:01 hat Ashish Mittal geschrieben:
> This patch adds support for a new block device type called "vxhs".
> Source code for the library that this code loads can be downloaded from:
> https://github.com/MittalAshish/libqnio.git
> 
> Version 2 patch submission fixes the following issues:
> (1) Removed code to dlopen library. We now check if libqnio is installed during
>     configure, and directly link with it.
> (2) Changed file headers to mention GPLv2-or-later license.
> (3) Removed unnecessary type casts and inlines.
> (4) Removed custom tokenize function and modified code to use g_strsplit.
> (5) Replaced malloc/free with g_new/g_free and removed code that checks for
>     memory allocation failure conditions.
> (6) Removed some block ops implementations that were place-holders only.
> (7) Removed all custom debug messages. Added new messages in block/trace-events
> (8) Other miscellaneous corrections.
> 
> TODO: QAPI changes and (fixes to) review comments from Stefan.
> Signed-off-by: Ashish Mittal <ashish.mittal@veritas.com>

I just had a very high level look at the driver, and maybe it's better
to discuss those general design points first before going to the details
of the actual code.


So perhaps the most important thing is that I'm wondering whether we
really got the right split between qemu and libqnio yet. Generally a
library should be agnostic regarding its users, but libqnio has quite a
few functions that contain 'qemu' in their name. To me, this is a sign
that they might fit better in the qemu block driver.

The effect of keeping these function in libqnio is that, for example,
you're reimplementing qemu's IO vector functions which you could
directly use from the block driver, or that you do manual request
splitting that the qemu block layer could be doing for you if you told
it what the maximum size is.


Another point is that these days it's preferrable to implement
.bdrv_co_preadv/pwritev rather than .bdrv_aio_readv/writev. Your native
interfaces seem to be already byte based, so this should be a good
match.

Kevin
diff mbox

Patch

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 2593a2f..5f83305 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -20,6 +20,7 @@  block-obj-$(CONFIG_RBD) += rbd.o
 block-obj-$(CONFIG_GLUSTERFS) += gluster.o
 block-obj-$(CONFIG_ARCHIPELAGO) += archipelago.o
 block-obj-$(CONFIG_LIBSSH2) += ssh.o
+block-obj-$(CONFIG_VXHS) += vxhs.o
 block-obj-y += accounting.o dirty-bitmap.o
 block-obj-y += write-threshold.o
 
@@ -43,3 +44,4 @@  block-obj-m        += dmg.o
 dmg.o-libs         := $(BZIP2_LIBS)
 qcow.o-libs        := -lz
 linux-aio.o-libs   := -laio
+vxhs.o-libs        := $(VXHS_LIBS)
diff --git a/block/trace-events b/block/trace-events
index 978ef4f..8f02725 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -114,3 +114,43 @@  qed_aio_write_data(void *s, void *acb, int ret, uint64_t offset, size_t len) "s
 qed_aio_write_prefill(void *s, void *acb, uint64_t start, size_t len, uint64_t offset) "s %p acb %p start %"PRIu64" len %zu offset %"PRIu64
 qed_aio_write_postfill(void *s, void *acb, uint64_t start, size_t len, uint64_t offset) "s %p acb %p start %"PRIu64" len %zu offset %"PRIu64
 qed_aio_write_main(void *s, void *acb, int ret, uint64_t offset, size_t len) "s %p acb %p ret %d offset %"PRIu64" len %zu"
+
+# block/vxhs.c
+vxhs_bdrv_init(int version) "Registering VxHS %d AIO driver"
+vxhs_iio_callback(int error, int reason) "ctx is NULL: error %d, reason %d"
+vxhs_setup_qnio(void *s) "Context to HyperScale IO manager = %p"
+vxhs_setup_qnio_nwerror(char c) "Could not initialize the network channel. Bailing out%c"
+vxhs_open_device_cmdline(const char *vxhs_uri) "Original command line : %s"
+vxhs_iio_callback_iofail(int err, int reason, void *acb, int seg) "Read/Write failed: error %d, reason %d, acb %p, segment %d"
+vxhs_iio_callback_retry(char *guid, void *acb) "vDisk %s, added acb %p to retry queue (5)"
+vxhs_iio_callback_chnlfail(int error) "QNIO channel failed, no i/o (%d)"
+vxhs_iio_callback_fail(int r, void *acb, int seg, uint64_t size, int err) " ALERT: reason = %d , acb = %p, acb->segments = %d, acb->size = %lu Error = %d"
+vxhs_fail_aio(char * guid, void *acb) "vDisk %s, failing acb %p"
+vxhs_iio_callback_ready(char *vd, int err) "async vxhs_iio_callback: IRP_VDISK_CHECK_IO_FAILOVER_READY completed for vdisk %s with error %d"
+vxhs_iio_callback_chnfail(int err, int error) "QNIO channel failed, no i/o %d, %d"
+vxhs_iio_callback_unknwn(int opcode, int err) "unexpected opcode %d, errno %d"
+vxhs_open_device_qnio(char *of_vsa_addr) "Could not open an QNIO connection to: %s"
+vxhs_create(const char *filename) "vxhs_create: came in to open file = %s"
+vxhs_open(const char *filename) "vxhs_vxhs_open: came in to open file = %s"
+vxhs_open_fail(int ret) "Could not open the device. Error = %d"
+vxhs_open_epipe(char c) "Could not create a pipe for device. bailing out%c"
+vxhs_aio_rw(char *guid, int iodir, uint64_t size, uint64_t offset) "vDisk %s, vDisk device is in failed state iodir = %d size = %lu offset = %lu"
+vxhs_aio_rw_retry(char *guid, void *acb, int queue) "vDisk %s, added acb %p to retry queue(%d)"
+vxhs_aio_rw_invalid(int req) "Invalid I/O request iodir %d"
+vxhs_aio_rw_ioerr(char *guid, int iodir, uint64_t size, uint64_t off, void *acb, int seg, int ret, int err) "IO ERROR (vDisk %s) FOR : Read/Write = %d size = %lu offset = %lu ACB = %p Segments = %d. Error = %d, errno = %d"
+vxhs_co_flush(char *guid, int ret, int err) "vDisk (%s) Flush ioctl failed ret = %d errno = %d"
+vxhs_co_flush_iocnt(int iocnt) "In the flush the IO count = %d"
+vxhs_get_vdisk_stat(char *guid, int ret, int err) "vDisk (%s) stat ioctl failed, ret = %d, errno = %d"
+vxhs_switch_storage_agent(char *ip, char *guid) "Query host %s for vdisk %s"
+vxhs_switch_storage_agent_failed(char *ip, char *guid, int res, int err) "Query to host %s for vdisk %s failed, res = %d, errno = %d"
+vxhs_failover_ioctl_cb(char *ip, char *guid) "Switched to storage server host-IP %s for vdisk %s"
+vxhs_failover_ioctl_cb_retry(char *guid) "failover_ioctl_cb: keep looking for io target for vdisk %s"
+vxhs_failover_io(char *vdisk) "I/O Failover starting for vDisk %s"
+vxhs_reopen_vdisk(char *ip) "Failed to connect to storage agent on host-ip %s"
+vxhs_reopen_vdisk_openfail(char *fname) "Failed to open vdisk device: %s"
+vxhs_build_io_target_list(int num, char *uri) "About to parse URI %d : %s"
+vxhs_handle_queued_ios(void *acb, int res) "Restarted acb %p res %d"
+vxhs_restart_aio(int dir, int res, int err) "IO ERROR FOR: Read/Write = %d Error = %d, errno = %d"
+vxhs_complete_aio(void *acb, uint64_t ret) "aio failed acb %p ret %ld"
+vxhs_aio_rw_iofail(char *guid) "vDisk %s, I/O operation failed."
+vxhs_aio_rw_devfail(char *guid, int dir, uint64_t size, uint64_t off) "vDisk %s, vDisk device failed iodir = %d size = %lu offset = %lu"
diff --git a/block/vxhs.c b/block/vxhs.c
new file mode 100644
index 0000000..9a82757
--- /dev/null
+++ b/block/vxhs.c
@@ -0,0 +1,1199 @@ 
+/*
+ * QEMU Block driver for Veritas HyperScale (VxHS)
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "vxhs.h"
+#include <qnio/qnio_api.h>
+#include "trace.h"
+
+/* qnio client ioapi_ctx */
+static void __attribute__((unused)) *global_qnio_ctx;
+
+/* insure init once */
+static pthread_mutex_t __attribute__((unused))  of_global_ctx_lock =
+    PTHREAD_MUTEX_INITIALIZER;
+
+/* HyperScale Driver Version */
+static const int __attribute__((unused)) vxhs_drv_version = 8895;
+
+/* vdisk prefix to pass to qnio */
+static const char vdisk_prefix[] = "/dev/of/vdisk";
+
+void vxhs_inc_acb_segment_count(void *ptr, int count)
+{
+    VXHSAIOCB *acb = ptr;
+    BDRVVXHSState *s = acb->common.bs->opaque;
+
+    VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+    acb->segments += count;
+    VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+}
+
+void vxhs_dec_acb_segment_count(void *ptr, int count)
+{
+    VXHSAIOCB *acb = ptr;
+    BDRVVXHSState *s = acb->common.bs->opaque;
+
+    VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+    acb->segments -= count;
+    VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+}
+
+int vxhs_dec_and_get_acb_segment_count(void *ptr, int count)
+{
+    VXHSAIOCB *acb = ptr;
+    BDRVVXHSState *s = acb->common.bs->opaque;
+    int segcount = 0;
+
+
+    VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+    acb->segments -= count;
+    segcount = acb->segments;
+    VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+
+    return segcount;
+}
+
+void vxhs_set_acb_buffer(void *ptr, void *buffer)
+{
+    VXHSAIOCB *acb = ptr;
+
+    acb->buffer = buffer;
+}
+
+void vxhs_inc_vdisk_iocount(void *ptr, uint32_t count)
+{
+    BDRVVXHSState *s = ptr;
+
+    VXHS_SPIN_LOCK(s->vdisk_lock);
+    s->vdisk_aio_count += count;
+    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+}
+
+void vxhs_dec_vdisk_iocount(void *ptr, uint32_t count)
+{
+    BDRVVXHSState *s = ptr;
+
+    VXHS_SPIN_LOCK(s->vdisk_lock);
+    s->vdisk_aio_count -= count;
+    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+}
+
+uint32_t vxhs_get_vdisk_iocount(void *ptr)
+{
+    BDRVVXHSState *s = ptr;
+    uint32_t count = 0;
+
+    VXHS_SPIN_LOCK(s->vdisk_lock);
+    count = s->vdisk_aio_count;
+    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+
+    return count;
+}
+
+void vxhs_iio_callback(uint32_t rfd, uint32_t reason, void *ctx, void *m)
+{
+    VXHSAIOCB *acb = NULL;
+    BDRVVXHSState *s = NULL;
+    int rv = 0;
+    int segcount = 0;
+    uint32_t error = 0;
+    uint32_t opcode = 0;
+
+    assert(m);
+    if (m) {
+        /* TODO: need common get message attrs, not two separate lib calls */
+        error = qemu_iio_extract_msg_error(m);
+        opcode = qemu_iio_extract_msg_opcode(m);
+    }
+    switch (opcode) {
+    case IRP_READ_REQUEST:
+    case IRP_WRITE_REQUEST:
+
+    /*
+     * ctx is VXHSAIOCB*
+     * ctx is NULL if error is VXERROR_CHANNEL_HUP or reason is IIO_REASON_HUP
+     */
+    if (ctx) {
+        acb = ctx;
+        s = acb->common.bs->opaque;
+    } else {
+        trace_vxhs_iio_callback(error, reason);
+        goto out;
+    }
+
+    if (error) {
+        trace_vxhs_iio_callback_iofail(error, reason, acb, acb->segments);
+
+        if (reason == IIO_REASON_DONE || reason == IIO_REASON_EVENT) {
+            /*
+             * Storage agent failed while I/O was in progress
+             * Fail over only if the qnio channel dropped, indicating
+             * storage agent failure. Don't fail over in response to other
+             * I/O errors such as disk failure.
+             */
+            if (error == VXERROR_RETRY_ON_SOURCE || error == VXERROR_HUP ||
+                error == VXERROR_CHANNEL_HUP || error == -1) {
+                /*
+                 * Start vDisk IO failover once callback is
+                 * called against all the pending IOs.
+                 * If vDisk has no redundency enabled
+                 * then IO failover routine will mark
+                 * the vDisk failed and fail all the
+                 * AIOs without retry (stateless vDisk)
+                 */
+                VXHS_SPIN_LOCK(s->vdisk_lock);
+                if (!OF_VDISK_IOFAILOVER_IN_PROGRESS(s)) {
+                    OF_VDISK_SET_IOFAILOVER_IN_PROGRESS(s);
+                }
+                /*
+                 * Check if this acb is already queued before.
+                 * It is possible in case if I/Os are submitted
+                 * in multiple segments (QNIO_MAX_IO_SIZE).
+                 */
+                VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+                if (!OF_AIOCB_FLAGS_QUEUED(acb)) {
+                    QSIMPLEQ_INSERT_TAIL(&s->vdisk_aio_retryq,
+                                         acb, retry_entry);
+                    OF_AIOCB_FLAGS_SET_QUEUED(acb);
+                    s->vdisk_aio_retry_qd++;
+                    trace_vxhs_iio_callback_retry(s->vdisk_guid, acb);
+                }
+                segcount = --acb->segments;
+                VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+                /*
+                 * Decrement AIO count only when callback is called
+                 * against all the segments of aiocb.
+                 */
+                if (segcount == 0 && --s->vdisk_aio_count == 0) {
+                    /*
+                     * Start vDisk I/O failover
+                     */
+                    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+                    /*
+                     * TODO:
+                     * Need to explore further if it is possible to optimize
+                     * the failover operation on Virtual-Machine (global)
+                     * specific rather vDisk specific.
+                     */
+                    vxhs_failover_io(s);
+                    goto out;
+                }
+                VXHS_SPIN_UNLOCK(s->vdisk_lock);
+                goto out;
+            }
+        } else if (reason == IIO_REASON_HUP) {
+            /*
+             * Channel failed, spontaneous notification,
+             * not in response to I/O
+             */
+            trace_vxhs_iio_callback_chnlfail(error);
+            /*
+             * TODO: Start channel failover when no I/O is outstanding
+             */
+            goto out;
+        } else {
+            trace_vxhs_iio_callback_fail(reason, acb, acb->segments, acb->size, error);
+        }
+    }
+    /*
+     * Set error into acb if not set. In case if acb is being
+     * submitted in multiple segments then need to set the error
+     * only once.
+     *
+     * Once acb done callback is called for the last segment
+     * then acb->ret return status will be sent back to the
+     * caller.
+     */
+    VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+    if (error && !acb->ret) {
+        acb->ret = error;
+    }
+    --acb->segments;
+    segcount = acb->segments;
+    assert(segcount >= 0);
+    VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+    /*
+     * Check if all the outstanding I/Os are done against acb.
+     * If yes then send signal for AIO completion.
+     */
+    if (segcount == 0) {
+        rv = qemu_write_full(s->fds[VDISK_FD_WRITE], &acb, sizeof(acb));
+        if (rv != sizeof(acb)) {
+            error_report("VXHS AIO completion failed: %s", strerror(errno));
+            abort();
+        }
+    }
+    break;
+
+    case IRP_VDISK_CHECK_IO_FAILOVER_READY:
+        /* ctx is BDRVVXHSState* */
+        assert(ctx);
+        trace_vxhs_iio_callback_ready(((BDRVVXHSState *)ctx)->vdisk_guid, error);
+        vxhs_failover_ioctl_cb(error, ctx);
+        break;
+
+    default:
+        if (reason == IIO_REASON_HUP) {
+            /*
+             * Channel failed, spontaneous notification,
+             * not in response to I/O
+             */
+            trace_vxhs_iio_callback_chnfail(error, errno);
+            /*
+             * TODO: Start channel failover when no I/O is outstanding
+             */
+        } else {
+            trace_vxhs_iio_callback_unknwn(opcode, error);
+        }
+        break;
+    }
+out:
+    return;
+}
+
+void vxhs_complete_aio(VXHSAIOCB *acb, BDRVVXHSState *s)
+{
+    BlockCompletionFunc *cb = acb->common.cb;
+    void *opaque = acb->common.opaque;
+    int ret = 0;
+
+    if (acb->ret != 0) {
+        trace_vxhs_complete_aio(acb, acb->ret);
+    /*
+     * We mask all the IO errors generically as EIO for upper layers
+     * Right now our IO Manager uses non standard error codes. Instead
+     * of confusing upper layers with incorrect interpretation we are
+     * doing this workaround.
+     */
+        ret = (-EIO);
+    }
+    /*
+     * Copy back contents from stablization buffer into original iovector
+     * before returning the IO
+     */
+    if (acb->buffer != NULL) {
+        qemu_iovec_from_buf(acb->qiov, 0, acb->buffer, acb->qiov->size);
+        free(acb->buffer);
+        acb->buffer = NULL;
+    }
+    vxhs_dec_vdisk_iocount(s, 1);
+    acb->aio_done = VXHS_IO_COMPLETED;
+    qemu_aio_unref(acb);
+    cb(opaque, ret);
+}
+
+/*
+ * This is the HyperScale event handler registered to QEMU.
+ * It is invoked when any IO gets completed and written on pipe
+ * by callback called from QNIO thread context. Then it marks
+ * the AIO as completed, and releases HyperScale AIO callbacks.
+ */
+void vxhs_aio_event_reader(void *opaque)
+{
+    BDRVVXHSState *s = opaque;
+    ssize_t ret;
+
+    do {
+        char *p = (char *)&s->qnio_event_acb;
+
+        ret = read(s->fds[VDISK_FD_READ], p + s->event_reader_pos,
+                   sizeof(s->qnio_event_acb) - s->event_reader_pos);
+        if (ret > 0) {
+            s->event_reader_pos += ret;
+            if (s->event_reader_pos == sizeof(s->qnio_event_acb)) {
+                s->event_reader_pos = 0;
+                vxhs_complete_aio(s->qnio_event_acb, s);
+            }
+        }
+    } while (ret < 0 && errno == EINTR);
+}
+
+/*
+ * QEMU calls this to check if there are any pending IO on vDisk.
+ * It will wait in a loop until all the AIOs are completed.
+ */
+int vxhs_aio_flush_cb(void *opaque)
+{
+    BDRVVXHSState *s = opaque;
+
+    return vxhs_get_vdisk_iocount(s);
+}
+
+/*
+ * This will be called by QEMU while booting for each vDisk.
+ * bs->opaque will be allocated by QEMU upper block layer before
+ * calling open. It will load all the QNIO operations from
+ * qemuqnio library and call QNIO operation to create channel to
+ * do IO on vDisk. It parses the URI, gets the hostname, vDisk
+ * path and then sets HyperScale event handler to QEMU.
+ */
+void *vxhs_setup_qnio(void)
+{
+    void *qnio_ctx = NULL;
+
+    qnio_ctx = qemu_iio_init(vxhs_iio_callback);
+
+    if (qnio_ctx != NULL) {
+        trace_vxhs_setup_qnio(qnio_ctx);
+    } else {
+        trace_vxhs_setup_qnio_nwerror('.');
+    }
+
+    return qnio_ctx;
+}
+
+int vxhs_open_device(const char *vxhs_uri, int *cfd, int *rfd,
+                       BDRVVXHSState *s)
+{
+    char *file_name;
+    char *of_vsa_addr;
+    int ret = 0;
+    gchar **target_list;
+
+    pthread_mutex_lock(&of_global_ctx_lock);
+    if (global_qnio_ctx == NULL) {
+        global_qnio_ctx = vxhs_setup_qnio();
+        if (global_qnio_ctx == NULL) {
+            pthread_mutex_unlock(&of_global_ctx_lock);
+            return -1;
+        }
+    }
+    pthread_mutex_unlock(&of_global_ctx_lock);
+
+    *cfd = -1;
+
+    of_vsa_addr = g_new0(char, OF_MAX_SERVER_ADDR);
+    file_name = g_new0(char, OF_MAX_FILE_LEN);
+
+    /*
+     * The steps below need to done by all the block drivers in QEMU which
+     * support AIO. Need to create pipe for communicating b/w two threads
+     * in different context. And set handler for read event when IO completion
+     * is reported by non-QEMU context.
+     */
+    trace_vxhs_open_device_cmdline(vxhs_uri);
+    target_list = g_strsplit(vxhs_uri, "%7D", 0);
+    assert(target_list != NULL && target_list[0] != NULL);
+    vxhs_build_io_target_list(s, target_list);
+
+    snprintf(file_name, OF_MAX_FILE_LEN, "%s%s", vdisk_prefix, s->vdisk_guid);
+    snprintf(of_vsa_addr, OF_MAX_SERVER_ADDR, "of://%s:%d",
+             s->vdisk_hostinfo[s->vdisk_cur_host_idx].hostip,
+             s->vdisk_hostinfo[s->vdisk_cur_host_idx].port);
+
+    *cfd = qemu_open_iio_conn(global_qnio_ctx, of_vsa_addr, 0);
+    if (*cfd < 0) {
+        trace_vxhs_open_device_qnio(of_vsa_addr);
+        ret = -EIO;
+        goto out;
+    }
+    *rfd = qemu_iio_devopen(global_qnio_ctx, *cfd, file_name, 0);
+    s->aio_context = qemu_get_aio_context();
+
+out:
+    /* uri is still in use, cleaned up in close */
+    if (file_name != NULL) {
+        g_free(file_name);
+    }
+    if (of_vsa_addr != NULL) {
+        g_free(of_vsa_addr);
+    }
+    g_strfreev(target_list);
+    return ret;
+}
+
+int vxhs_create(const char *filename,
+        QemuOpts *options, Error **errp)
+{
+        int ret = 0;
+        int qemu_cfd = 0;
+        int qemu_rfd = 0;
+        BDRVVXHSState s;
+
+        trace_vxhs_create(filename);
+        ret = vxhs_open_device(filename, &qemu_cfd, &qemu_rfd, &s);
+
+        return ret;
+}
+
+static QemuOptsList runtime_opts = {
+    .name = "vxhs",
+    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
+    .desc = {
+        {
+            .name = "filename",
+            .type = QEMU_OPT_STRING,
+            .help = "URI to the Veritas HyperScale image",
+        },
+        { /* end of list */ }
+    },
+};
+
+int vxhs_open(BlockDriverState *bs, QDict *options,
+              int bdrv_flags, Error **errp)
+{
+    BDRVVXHSState *s = bs->opaque;
+    int ret = 0;
+    int qemu_qnio_cfd = 0;
+    int qemu_rfd = 0;
+    QemuOpts *opts;
+    Error *local_err = NULL;
+    const char *vxhs_uri;
+
+    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+    qemu_opts_absorb_qdict(opts, options, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        ret = -EINVAL;
+        goto out;
+    }
+
+    vxhs_uri = qemu_opt_get(opts, "filename");
+
+    memset(s, 0, sizeof(*s));
+    trace_vxhs_open(vxhs_uri);
+    ret = vxhs_open_device(vxhs_uri, &qemu_qnio_cfd, &qemu_rfd, s);
+    if (ret != 0) {
+        trace_vxhs_open_fail(ret);
+        return ret;
+    }
+    s->qnio_ctx = global_qnio_ctx;
+    s->vdisk_hostinfo[0].qnio_cfd = qemu_qnio_cfd;
+    s->vdisk_hostinfo[0].vdisk_rfd = qemu_rfd;
+    s->vdisk_size = 0;
+    QSIMPLEQ_INIT(&s->vdisk_aio_retryq);
+
+    ret = qemu_pipe(s->fds);
+    if (ret < 0) {
+        trace_vxhs_open_epipe('.');
+        ret = -errno;
+        goto out;
+    }
+    fcntl(s->fds[VDISK_FD_READ], F_SETFL, O_NONBLOCK);
+
+    aio_set_fd_handler(s->aio_context, s->fds[VDISK_FD_READ],
+                       false, vxhs_aio_event_reader, NULL, s);
+
+    /*
+     * Allocate/Initialize the spin-locks.
+     *
+     * NOTE:
+     *      Since spin lock is being allocated
+     *      dynamically hence moving acb struct
+     *      specific lock to BDRVVXHSState
+     *      struct. The reason being,
+     *      we don't want the overhead of spin
+     *      lock being dynamically allocated and
+     *      freed for every AIO.
+     */
+    s->vdisk_lock = VXHS_SPIN_LOCK_ALLOC;
+    s->vdisk_acb_lock = VXHS_SPIN_LOCK_ALLOC;
+
+    return 0;
+
+out:
+    if (s->vdisk_hostinfo[0].vdisk_rfd >= 0) {
+        qemu_iio_devclose(s->qnio_ctx, 0,
+                                 s->vdisk_hostinfo[0].vdisk_rfd);
+    }
+    /* never close qnio_cfd */
+    trace_vxhs_open_fail(ret);
+    return ret;
+}
+
+static const AIOCBInfo vxhs_aiocb_info = {
+    .aiocb_size = sizeof(VXHSAIOCB)
+};
+
+/*
+ * This is called in QNIO thread context when IO done
+ * on IO Manager and QNIO client received the data or
+ * ACK. It notify another event handler thread running in QEMU context
+ * by writing on the pipe
+ */
+void vxhs_finish_aiocb(ssize_t ret, void *arg)
+{
+    VXHSAIOCB *acb = arg;
+    BlockDriverState *bs = acb->common.bs;
+    BDRVVXHSState *s = bs->opaque;
+    int rv;
+
+    acb->ret = ret;
+    rv = qemu_write_full(s->fds[VDISK_FD_WRITE], &acb, sizeof(acb));
+    if (rv != sizeof(acb)) {
+        error_report("VXHS AIO completion failed: %s",
+                     strerror(errno));
+        abort();
+    }
+}
+
+/*
+ * This allocates QEMU-VXHS callback for each IO
+ * and is passed to QNIO. When QNIO completes the work,
+ * it will be passed back through the callback.
+ */
+BlockAIOCB *vxhs_aio_rw(BlockDriverState *bs,
+                                int64_t sector_num, QEMUIOVector *qiov,
+                                int nb_sectors,
+                                BlockCompletionFunc *cb,
+                                void *opaque, int iodir)
+{
+    VXHSAIOCB         *acb = NULL;
+    BDRVVXHSState     *s = bs->opaque;
+    size_t              size;
+    uint64_t            offset;
+    int                 iio_flags = 0;
+    int                 ret = 0;
+
+    offset = sector_num * BDRV_SECTOR_SIZE;
+    size = nb_sectors * BDRV_SECTOR_SIZE;
+
+    acb = qemu_aio_get(&vxhs_aiocb_info, bs, cb, opaque);
+    /*
+     * Setup or initialize VXHSAIOCB.
+     * Every single field should be initialized since
+     * acb will be picked up from the slab without
+     * initializing with zero.
+     */
+    acb->io_offset = offset;
+    acb->size = size;
+    acb->ret = 0;
+    acb->flags = 0;
+    acb->aio_done = VXHS_IO_INPROGRESS;
+    acb->segments = 0;
+    acb->buffer = 0;
+    acb->qiov = qiov;
+    acb->direction = iodir;
+
+    VXHS_SPIN_LOCK(s->vdisk_lock);
+    if (OF_VDISK_FAILED(s)) {
+        trace_vxhs_aio_rw(s->vdisk_guid, iodir, size, offset);
+        VXHS_SPIN_UNLOCK(s->vdisk_lock);
+        goto errout;
+    }
+    if (OF_VDISK_IOFAILOVER_IN_PROGRESS(s)) {
+        QSIMPLEQ_INSERT_TAIL(&s->vdisk_aio_retryq, acb, retry_entry);
+        s->vdisk_aio_retry_qd++;
+        OF_AIOCB_FLAGS_SET_QUEUED(acb);
+        VXHS_SPIN_UNLOCK(s->vdisk_lock);
+        trace_vxhs_aio_rw_retry(s->vdisk_guid, acb, 1);
+        goto out;
+    }
+    s->vdisk_aio_count++;
+    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+
+    iio_flags = (IIO_FLAG_DONE | IIO_FLAG_ASYNC);
+
+    switch (iodir) {
+    case VDISK_AIO_WRITE:
+            vxhs_inc_acb_segment_count(acb, 1);
+            ret = qemu_iio_writev(s->qnio_ctx,
+                    s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+                    qiov->iov, qiov->niov, offset, (void *)acb, iio_flags);
+            break;
+    case VDISK_AIO_READ:
+            vxhs_inc_acb_segment_count(acb, 1);
+            ret = qemu_iio_readv(s->qnio_ctx,
+                    s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+                    qiov->iov, qiov->niov, offset, (void *)acb, iio_flags);
+            break;
+    default:
+            trace_vxhs_aio_rw_invalid(iodir);
+            goto errout;
+    }
+
+    if (ret != 0) {
+        trace_vxhs_aio_rw_ioerr(
+                  s->vdisk_guid, iodir, size, offset,
+                  acb, acb->segments, ret, errno);
+        /*
+         * Don't retry I/Os against vDisk having no
+         * redundency or statefull storage on compute
+         *
+         * TODO: Revisit this code path to see if any
+         *       particular error needs to be handled.
+         *       At this moment failing the I/O.
+         */
+        VXHS_SPIN_LOCK(s->vdisk_lock);
+        if (s->vdisk_nhosts == 1) {
+            trace_vxhs_aio_rw_iofail(s->vdisk_guid);
+            s->vdisk_aio_count--;
+            vxhs_dec_acb_segment_count(acb, 1);
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            goto errout;
+        }
+        if (OF_VDISK_FAILED(s)) {
+            trace_vxhs_aio_rw_devfail(
+                      s->vdisk_guid, iodir, size, offset);
+            s->vdisk_aio_count--;
+            vxhs_dec_acb_segment_count(acb, 1);
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            goto errout;
+        }
+        if (OF_VDISK_IOFAILOVER_IN_PROGRESS(s)) {
+            /*
+             * Queue all incoming io requests after failover starts.
+             * Number of requests that can arrive is limited by io queue depth
+             * so an app blasting independent ios will not exhaust memory.
+             */
+            QSIMPLEQ_INSERT_TAIL(&s->vdisk_aio_retryq, acb, retry_entry);
+            s->vdisk_aio_retry_qd++;
+            OF_AIOCB_FLAGS_SET_QUEUED(acb);
+            s->vdisk_aio_count--;
+            vxhs_dec_acb_segment_count(acb, 1);
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            trace_vxhs_aio_rw_retry(s->vdisk_guid, acb, 2);
+            goto out;
+        }
+        OF_VDISK_SET_IOFAILOVER_IN_PROGRESS(s);
+        QSIMPLEQ_INSERT_TAIL(&s->vdisk_aio_retryq, acb, retry_entry);
+        s->vdisk_aio_retry_qd++;
+        OF_AIOCB_FLAGS_SET_QUEUED(acb);
+        vxhs_dec_acb_segment_count(acb, 1);
+        trace_vxhs_aio_rw_retry(s->vdisk_guid, acb, 3);
+        /*
+         * Start I/O failover if there is no active
+         * AIO within vxhs block driver.
+         */
+        if (--s->vdisk_aio_count == 0) {
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            /*
+             * Start IO failover
+             */
+            vxhs_failover_io(s);
+            goto out;
+        }
+        VXHS_SPIN_UNLOCK(s->vdisk_lock);
+    }
+
+out:
+    return &acb->common;
+
+errout:
+    qemu_aio_unref(acb);
+    return NULL;
+}
+
+BlockAIOCB *vxhs_aio_readv(BlockDriverState *bs,
+                                   int64_t sector_num, QEMUIOVector *qiov,
+                                   int nb_sectors,
+                                   BlockCompletionFunc *cb, void *opaque)
+{
+    return vxhs_aio_rw(bs, sector_num, qiov, nb_sectors,
+                         cb, opaque, VDISK_AIO_READ);
+}
+
+BlockAIOCB *vxhs_aio_writev(BlockDriverState *bs,
+                                    int64_t sector_num, QEMUIOVector *qiov,
+                                    int nb_sectors,
+                                    BlockCompletionFunc *cb, void *opaque)
+{
+    return vxhs_aio_rw(bs, sector_num, qiov, nb_sectors,
+                         cb, opaque, VDISK_AIO_WRITE);
+}
+
+/*
+ * This is called by QEMU when a flush gets triggered from within
+ * a guest at the block layer, either for IDE or SCSI disks.
+ */
+int vxhs_co_flush(BlockDriverState *bs)
+{
+    BDRVVXHSState *s = bs->opaque;
+    uint64_t size = 0;
+    int ret = 0;
+    uint32_t iocount = 0;
+
+    ret = qemu_iio_ioctl(s->qnio_ctx,
+            s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+            VDISK_AIO_FLUSH, &size, NULL, IIO_FLAG_SYNC);
+
+    if (ret < 0) {
+        /*
+         * Currently not handling the flush ioctl
+         * failure because of network connection
+         * disconnect. Since all the writes are
+         * commited into persistent storage hence
+         * this flush call is noop and we can safely
+         * return success status to the caller.
+         *
+         * If any write failure occurs for inflight
+         * write AIO because of network disconnect
+         * then anyway IO failover will be triggered.
+         */
+        trace_vxhs_co_flush(s->vdisk_guid, ret, errno);
+        ret = 0;
+    }
+
+    iocount = vxhs_get_vdisk_iocount(s);
+    if (iocount > 0) {
+        trace_vxhs_co_flush_iocnt(iocount);
+    }
+
+    return ret;
+}
+
+/*
+ * This is called by guest or QEMU to free blocks.
+ * When block freed when files deleted in the guest, fstrim utility
+ * can be used to pass the hints to the block layer if the disk supports
+ * TRIM. It send WRITE_SAME SCSI command to QEMU virtio-scsi layer, which
+ * call bdrv_aio_discard interface.
+ */
+coroutine_fn int vxhs_co_pdiscard(BlockDriverState *bs,
+                                   int64_t sector_num, int nb_sectors)
+{
+    int64_t off, size;
+
+    off = sector_num * BDRV_SECTOR_SIZE;
+    size = nb_sectors * BDRV_SECTOR_SIZE;
+
+    vxhsErr("We are faking the discard for range off = %lu "
+              "for %lu bytes\n", off, size);
+    vxhsErr("returning from discard\n");
+
+    return 0;
+}
+
+unsigned long vxhs_get_vdisk_stat(BDRVVXHSState *s)
+{
+    void *ctx = NULL;
+    int flags = 0;
+    unsigned long vdisk_size = 0;
+    int ret = 0;
+
+    ret = qemu_iio_ioctl(s->qnio_ctx,
+            s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+            VDISK_STAT, &vdisk_size, ctx, flags);
+
+    if (ret < 0) {
+        trace_vxhs_get_vdisk_stat(s->vdisk_guid, ret, errno);
+    }
+
+    return vdisk_size;
+}
+
+/*
+ * Returns the size of vDisk in bytes. This is required
+ * by QEMU block upper block layer so that it is visible
+ * to guest.
+ */
+int64_t vxhs_getlength(BlockDriverState *bs)
+{
+    BDRVVXHSState *s = bs->opaque;
+    unsigned long vdisk_size = 0;
+
+    if (s->vdisk_size > 0) {
+        vdisk_size = s->vdisk_size;
+    } else {
+        /*
+         * Fetch the vDisk size using stat ioctl
+         */
+        vdisk_size = vxhs_get_vdisk_stat(s);
+        if (vdisk_size > 0) {
+            s->vdisk_size = vdisk_size;
+        }
+    }
+
+    if (vdisk_size > 0) {
+        return (int64_t)vdisk_size; /* return size in bytes */
+    } else {
+        return -EIO;
+    }
+}
+
+/*
+ * Returns actual blocks allocated for the vDisk.
+ * This is required by qemu-img utility.
+ */
+int64_t vxhs_get_allocated_blocks(BlockDriverState *bs)
+{
+    BDRVVXHSState *s = bs->opaque;
+    unsigned long vdisk_size = 0;
+
+    if (s->vdisk_size > 0) {
+        vdisk_size = s->vdisk_size;
+    } else {
+        /*
+         * TODO:
+         * Once HyperScale storage-virtualizer provides
+         * actual physical allocation of blocks then
+         * fetch that information and return back to the
+         * caller but for now just get the full size.
+         */
+        vdisk_size = vxhs_get_vdisk_stat(s);
+        if (vdisk_size > 0) {
+            s->vdisk_size = vdisk_size;
+        }
+    }
+
+    if (vdisk_size > 0) {
+        return (int64_t)vdisk_size; /* return size in bytes */
+    } else {
+        return -EIO;
+    }
+}
+
+void vxhs_close(BlockDriverState *bs)
+{
+    BDRVVXHSState *s = bs->opaque;
+
+    close(s->fds[VDISK_FD_READ]);
+    close(s->fds[VDISK_FD_WRITE]);
+
+    /*
+     * never close channel - not ref counted, will
+     * close for all vdisks
+     */
+    if (s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd >= 0) {
+        qemu_iio_devclose(s->qnio_ctx, 0,
+            s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd);
+    }
+    if (s->vdisk_lock) {
+        VXHS_SPIN_LOCK_DESTROY(s->vdisk_lock);
+        s->vdisk_lock = NULL;
+    }
+    if (s->vdisk_acb_lock) {
+        VXHS_SPIN_LOCK_DESTROY(s->vdisk_acb_lock);
+        s->vdisk_acb_lock = NULL;
+    }
+
+    /*
+     * TODO: Verify that all the resources were relinguished.
+     */
+}
+
+/*
+ * If errors are consistent with storage agent failure:
+ *  - Try to reconnect in case error is transient or storage agent restarted.
+ *  - Currently failover is being triggered on per vDisk basis. There is
+ *    a scope of further optimization where failover can be global (per VM).
+ *  - In case of network (storage agent) failure, for all the vDisks, having
+ *    no redundency, I/Os will be failed without attempting for I/O failover
+ *    because of stateless nature of vDisk.
+ *  - If local or source storage agent is down then send an ioctl to remote
+ *    storage agent to check if remote storage agent in a state to accept
+ *    application I/Os.
+ *  - Once remote storage agent is ready to accept I/O, start I/O shipping.
+ *  - If I/Os cannot be serviced then vDisk will be marked failed so that
+ *    new incoming I/Os are returned with failure immediately.
+ *  - If vDisk I/O failover is in progress then all new/inflight I/Os will
+ *    queued and will be restarted or failed based on failover operation
+ *    is successful or not.
+ *  - I/O failover can be started either in I/O forward or I/O backward
+ *    path.
+ *  - I/O failover will be started as soon as all the pending acb(s)
+ *    are queued and there is no pending I/O count.
+ *  - If I/O failover couldn't be completed within QNIO_CONNECT_TIMOUT_SECS
+ *    then vDisk will be marked failed and all I/Os will be completed with
+ *    error.
+ */
+
+int vxhs_switch_storage_agent(BDRVVXHSState *s)
+{
+    int res = 0;
+    int flags = (IIO_FLAG_ASYNC | IIO_FLAG_DONE);
+
+    trace_vxhs_switch_storage_agent(
+              s->vdisk_hostinfo[s->vdisk_ask_failover_idx].hostip,
+              s->vdisk_guid);
+
+    res = vxhs_reopen_vdisk(s, s->vdisk_ask_failover_idx);
+    if (res == 0) {
+        res = qemu_iio_ioctl(s->qnio_ctx,
+                   s->vdisk_hostinfo[s->vdisk_ask_failover_idx].vdisk_rfd,
+                   VDISK_CHECK_IO_FAILOVER_READY, NULL, s, flags);
+    }
+    if (res != 0) {
+    trace_vxhs_switch_storage_agent_failed(
+                  s->vdisk_hostinfo[s->vdisk_ask_failover_idx].hostip,
+                  s->vdisk_guid, res, errno);
+        /*
+         * TODO: calling vxhs_failover_ioctl_cb from here ties up the qnio epoll
+         * loop if qemu_iio_ioctl fails synchronously (-1) for all hosts in io
+         * target list.
+         */
+
+        /* try next host */
+        vxhs_failover_ioctl_cb(res, s);
+    }
+    return res;
+}
+
+void vxhs_failover_ioctl_cb(int res, void *ctx)
+{
+    BDRVVXHSState *s = ctx;
+
+    if (res == 0) {
+        /* found failover target */
+        s->vdisk_cur_host_idx = s->vdisk_ask_failover_idx;
+        s->vdisk_ask_failover_idx = 0;
+        trace_vxhs_failover_ioctl_cb(
+                   s->vdisk_hostinfo[s->vdisk_cur_host_idx].hostip,
+                   s->vdisk_guid);
+        VXHS_SPIN_LOCK(s->vdisk_lock);
+        OF_VDISK_RESET_IOFAILOVER_IN_PROGRESS(s);
+        VXHS_SPIN_UNLOCK(s->vdisk_lock);
+        vxhs_handle_queued_ios(s);
+    } else {
+        /* keep looking */
+        trace_vxhs_failover_ioctl_cb_retry(s->vdisk_guid);
+        s->vdisk_ask_failover_idx++;
+        if (s->vdisk_ask_failover_idx == s->vdisk_nhosts) {
+            /* pause and cycle through list again */
+            sleep(QNIO_CONNECT_RETRY_SECS);
+            s->vdisk_ask_failover_idx = 0;
+        }
+        res = vxhs_switch_storage_agent(s);
+    }
+}
+
+int vxhs_failover_io(BDRVVXHSState *s)
+{
+    int res = 0;
+
+    trace_vxhs_failover_io(s->vdisk_guid);
+
+    s->vdisk_ask_failover_idx = 0;
+    res = vxhs_switch_storage_agent(s);
+
+    return res;
+}
+
+/*
+ * Try to reopen the vDisk on one of the available hosts
+ * If vDisk reopen is successful on any of the host then
+ * check if that node is ready to accept I/O.
+ */
+int vxhs_reopen_vdisk(BDRVVXHSState *s, int index)
+{
+    char *of_vsa_addr = NULL;
+    char *file_name = NULL;
+    int  res = 0;
+
+    /*
+     * Don't close the channel if it was opened
+     * before successfully. It will be handled
+     * within iio* api if the same channel open
+     * fd is reused.
+     *
+     * close stale vdisk device remote fd since
+     * it is invalid after channel disconnect.
+     */
+    if (s->vdisk_hostinfo[index].vdisk_rfd >= 0) {
+        qemu_iio_devclose(s->qnio_ctx, 0,
+                                 s->vdisk_hostinfo[index].vdisk_rfd);
+        s->vdisk_hostinfo[index].vdisk_rfd = -1;
+    }
+    /*
+     * build storage agent address and vdisk device name strings
+     */
+    of_vsa_addr = g_new0(char, OF_MAX_SERVER_ADDR);
+    file_name = g_new0(char, OF_MAX_FILE_LEN);
+    snprintf(file_name, OF_MAX_FILE_LEN, "%s%s", vdisk_prefix, s->vdisk_guid);
+    snprintf(of_vsa_addr, OF_MAX_SERVER_ADDR, "of://%s:%d",
+             s->vdisk_hostinfo[index].hostip, s->vdisk_hostinfo[index].port);
+    /*
+     * open qnio channel to storage agent if not opened before.
+     */
+    if (s->vdisk_hostinfo[index].qnio_cfd < 0) {
+        s->vdisk_hostinfo[index].qnio_cfd =
+                qemu_open_iio_conn(global_qnio_ctx, of_vsa_addr, 0);
+        if (s->vdisk_hostinfo[index].qnio_cfd < 0) {
+            trace_vxhs_reopen_vdisk(s->vdisk_hostinfo[index].hostip);
+            res = ENODEV;
+            goto out;
+        }
+    }
+    /*
+     * open vdisk device
+     */
+    s->vdisk_hostinfo[index].vdisk_rfd =
+            qemu_iio_devopen(global_qnio_ctx,
+             s->vdisk_hostinfo[index].qnio_cfd, file_name, 0);
+    if (s->vdisk_hostinfo[index].vdisk_rfd < 0) {
+        trace_vxhs_reopen_vdisk_openfail(file_name);
+        res = EIO;
+        goto out;
+    }
+out:
+    if (of_vsa_addr) {
+        g_free(of_vsa_addr);
+    }
+    if (file_name) {
+        g_free(file_name);
+    }
+    return res;
+}
+
+/*
+ * vxhs_build_io_target_list: Initialize io target list with ip addresses of
+ * local storage agent and reflection target storage agents. The local storage
+ * agent ip is the efficient internal address in the uri, e.g. 192.168.0.2.
+ * The local storage agent address is stored at index 0. The reflection target
+ * ips, are the E-W data network addresses of the reflection node agents, also
+ * extracted from the uri.
+ */
+int vxhs_build_io_target_list(BDRVVXHSState *s, char **filenames)
+{
+    URI *uri = NULL;
+    int i = 0;
+
+    for (i = 0; filenames[i] != NULL && *filenames[i]; i++) {
+        trace_vxhs_build_io_target_list(i+1, filenames[i]);
+        uri = uri_parse(filenames[i]);
+        assert(uri != NULL && uri->server != NULL);
+        s->vdisk_hostinfo[i].hostip = g_new0(char, strlen(uri->server));
+        strncpy((s->vdisk_hostinfo[i].hostip), uri->server, IP_ADDR_LEN);
+        s->vdisk_hostinfo[i].port = uri->port;
+        s->vdisk_hostinfo[i].qnio_cfd = -1;
+        s->vdisk_hostinfo[i].vdisk_rfd = -1;
+        if (i==0 && (strstr(uri->path, "vxhs") == NULL)) {
+            s->vdisk_guid = g_new0(char, strlen(uri->path)+3);
+            strcpy((s->vdisk_guid), uri->path);
+            strcat((s->vdisk_guid), "}");
+        }
+        uri_free(uri);
+    }
+    s->vdisk_nhosts = i;
+    s->vdisk_cur_host_idx = 0;
+
+   return 0;
+}
+
+int vxhs_handle_queued_ios(BDRVVXHSState *s)
+{
+    VXHSAIOCB *acb = NULL;
+    int res = 0;
+
+    VXHS_SPIN_LOCK(s->vdisk_lock);
+    while ((acb = QSIMPLEQ_FIRST(&s->vdisk_aio_retryq)) != NULL) {
+        /*
+         * Before we process the acb, check whether I/O failover
+         * started again due to failback or cascading failure.
+         */
+        if (OF_VDISK_IOFAILOVER_IN_PROGRESS(s)) {
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            goto out;
+        }
+        QSIMPLEQ_REMOVE_HEAD(&s->vdisk_aio_retryq, retry_entry);
+        s->vdisk_aio_retry_qd--;
+        OF_AIOCB_FLAGS_RESET_QUEUED(acb);
+        if (OF_VDISK_FAILED(s)) {
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            vxhs_fail_aio(acb, EIO);
+            VXHS_SPIN_LOCK(s->vdisk_lock);
+        } else {
+            VXHS_SPIN_UNLOCK(s->vdisk_lock);
+            res = vxhs_restart_aio(acb);
+            trace_vxhs_handle_queued_ios(acb, res);
+            VXHS_SPIN_LOCK(s->vdisk_lock);
+            if (res) {
+                QSIMPLEQ_INSERT_TAIL(&s->vdisk_aio_retryq,
+                                     acb, retry_entry);
+                OF_AIOCB_FLAGS_SET_QUEUED(acb);
+                VXHS_SPIN_UNLOCK(s->vdisk_lock);
+                goto out;
+            }
+        }
+    }
+    VXHS_SPIN_UNLOCK(s->vdisk_lock);
+out:
+    return res;
+}
+
+int vxhs_restart_aio(VXHSAIOCB *acb)
+{
+    BDRVVXHSState *s = NULL;
+    int iio_flags = 0;
+    int res = 0;
+
+    s = acb->common.bs->opaque;
+
+    if (acb->direction == VDISK_AIO_WRITE) {
+        vxhs_inc_vdisk_iocount(s, 1);
+        vxhs_inc_acb_segment_count(acb, 1);
+        iio_flags = (IIO_FLAG_DONE | IIO_FLAG_ASYNC);
+        res = qemu_iio_writev(s->qnio_ctx,
+                s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+                acb->qiov->iov, acb->qiov->niov,
+                acb->io_offset, (void *)acb, iio_flags);
+    }
+
+    if (acb->direction == VDISK_AIO_READ) {
+        vxhs_inc_vdisk_iocount(s, 1);
+        vxhs_inc_acb_segment_count(acb, 1);
+        iio_flags = (IIO_FLAG_DONE | IIO_FLAG_ASYNC);
+        res = qemu_iio_readv(s->qnio_ctx,
+                s->vdisk_hostinfo[s->vdisk_cur_host_idx].vdisk_rfd,
+                acb->qiov->iov, acb->qiov->niov,
+                acb->io_offset, (void *)acb, iio_flags);
+    }
+
+    if (res != 0) {
+        vxhs_dec_vdisk_iocount(s, 1);
+        vxhs_dec_acb_segment_count(acb, 1);
+        trace_vxhs_restart_aio(acb->direction, res, errno);
+    }
+
+    return res;
+}
+
+void vxhs_fail_aio(VXHSAIOCB *acb, int err)
+{
+    BDRVVXHSState *s = NULL;
+    int segcount = 0;
+    int rv = 0;
+
+    s = acb->common.bs->opaque;
+
+    trace_vxhs_fail_aio(s->vdisk_guid, acb);
+    if (!acb->ret) {
+        acb->ret = err;
+    }
+    VXHS_SPIN_LOCK(s->vdisk_acb_lock);
+    segcount = acb->segments;
+    VXHS_SPIN_UNLOCK(s->vdisk_acb_lock);
+    if (segcount == 0) {
+        /*
+         * Complete the io request
+         */
+        rv = qemu_write_full(s->fds[VDISK_FD_WRITE], &acb, sizeof(acb));
+        if (rv != sizeof(acb)) {
+            error_report("VXHS AIO completion failed: %s",
+                         strerror(errno));
+            abort();
+        }
+    }
+}
+
+static BlockDriver bdrv_vxhs = {
+    .format_name                  = "vxhs",
+    .protocol_name                = "vxhs",
+    .instance_size                = sizeof(BDRVVXHSState),
+    .bdrv_file_open               = vxhs_open,
+    .bdrv_create                  = vxhs_create,
+    .bdrv_close                   = vxhs_close,
+    .bdrv_getlength               = vxhs_getlength,
+    .bdrv_get_allocated_file_size = vxhs_get_allocated_blocks,
+    .bdrv_aio_readv               = vxhs_aio_readv,
+    .bdrv_aio_writev              = vxhs_aio_writev,
+    .bdrv_co_flush_to_disk        = vxhs_co_flush,
+    .bdrv_co_pdiscard             = vxhs_co_pdiscard,
+};
+
+void bdrv_vxhs_init(void)
+{
+    trace_vxhs_bdrv_init(vxhs_drv_version);
+    bdrv_register(&bdrv_vxhs);
+}
+
+/*
+ * The line below is how our drivier is initialized.
+ * DO NOT TOUCH IT
+ */
+block_init(bdrv_vxhs_init);
diff --git a/block/vxhs.h b/block/vxhs.h
new file mode 100644
index 0000000..2979f76
--- /dev/null
+++ b/block/vxhs.h
@@ -0,0 +1,294 @@ 
+/*
+ * QEMU Block driver for Veritas HyperScale (VxHS)
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef VXHSD_H
+#define VXHSD_H
+
+#include <gmodule.h>
+#include <inttypes.h>
+#include <pthread.h>
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/error-report.h"
+#include "block/block_int.h"
+#include "qemu/uri.h"
+#include "qemu/queue.h"
+
+#define vxhsErr(fmt, ...) { \
+    time_t t = time(0); \
+    char buf[9] = {0}; \
+    strftime(buf, 9, "%H:%M:%S", localtime(&t)); \
+    fprintf(stderr, "[%s: %lu] %d: %s():\t", buf, pthread_self(), \
+                __LINE__, __func__); \
+    fprintf(stderr, fmt, ## __VA_ARGS__); \
+}
+
+#define OF_GUID_STR_LEN             40
+#define OF_GUID_STR_SZ              (OF_GUID_STR_LEN + 1)
+#define QNIO_CONNECT_RETRY_SECS     5
+#define QNIO_CONNECT_TIMOUT_SECS    120
+
+/* constants from io_qnio.h */
+#define IIO_REASON_DONE     0x00000004
+#define IIO_REASON_EVENT    0x00000008
+#define IIO_REASON_HUP      0x00000010
+
+/*
+ * IO specific flags
+ */
+#define IIO_FLAG_ASYNC      0x00000001
+#define IIO_FLAG_DONE       0x00000010
+#define IIO_FLAG_SYNC       0
+
+/* constants from error.h */
+#define VXERROR_RETRY_ON_SOURCE     44
+#define VXERROR_HUP                 901
+#define VXERROR_CHANNEL_HUP         903
+
+/* constants from iomgr.h and opcode.h */
+#define IRP_READ_REQUEST                    0x1FFF
+#define IRP_WRITE_REQUEST                   0x2FFF
+#define IRP_VDISK_CHECK_IO_FAILOVER_READY   2020
+
+/* Lock specific macros */
+#define VXHS_SPIN_LOCK_ALLOC                  \
+    (qemu_ck_initialize_lock())
+#define VXHS_SPIN_LOCK(lock)                  \
+    (qemu_ck_spin_lock(lock))
+#define VXHS_SPIN_UNLOCK(lock)                \
+    (qemu_ck_spin_unlock(lock))
+#define VXHS_SPIN_LOCK_DESTROY(lock)          \
+    (qemu_ck_destroy_lock(lock))
+
+typedef enum {
+    VDISK_AIO_READ,
+    VDISK_AIO_WRITE,
+    VDISK_STAT,
+    VDISK_TRUNC,
+    VDISK_AIO_FLUSH,
+    VDISK_AIO_RECLAIM,
+    VDISK_GET_GEOMETRY,
+    VDISK_CHECK_IO_FAILOVER_READY,
+    VDISK_AIO_LAST_CMD
+} VDISKAIOCmd;
+
+typedef enum {
+    VXHS_IO_INPROGRESS,
+    VXHS_IO_COMPLETED,
+    VXHS_IO_ERROR
+} VXHSIOState;
+
+
+typedef void *qemu_aio_ctx_t;
+typedef void (*qnio_callback_t)(ssize_t retval, void *arg);
+
+#define VDISK_FD_READ 0
+#define VDISK_FD_WRITE 1
+
+#define QNIO_VDISK_NONE        0x00
+#define QNIO_VDISK_CREATE      0x01
+
+/* max IO size supported by QEMU NIO lib */
+#define QNIO_MAX_IO_SIZE       4194304
+
+#define IP_ADDR_LEN             20
+#define OF_MAX_FILE_LEN         1024
+#define OF_MAX_SERVER_ADDR      1024
+#define MAX_HOSTS               4
+
+/*
+ * Opcodes for making IOCTL on QEMU NIO library
+ */
+#define BASE_OPCODE_SHARED     1000
+#define BASE_OPCODE_DAL        2000
+#define IRP_VDISK_STAT                  (BASE_OPCODE_SHARED + 5)
+#define IRP_VDISK_GET_GEOMETRY          (BASE_OPCODE_DAL + 17)
+#define IRP_VDISK_READ_PARTITION        (BASE_OPCODE_DAL + 18)
+#define IRP_VDISK_FLUSH                 (BASE_OPCODE_DAL + 19)
+
+/*
+ * BDRVVXHSState specific flags
+ */
+#define OF_VDISK_FLAGS_STATE_ACTIVE             0x0000000000000001
+#define OF_VDISK_FLAGS_STATE_FAILED             0x0000000000000002
+#define OF_VDISK_FLAGS_IOFAILOVER_IN_PROGRESS   0x0000000000000004
+
+#define OF_VDISK_ACTIVE(s)                                              \
+        ((s)->vdisk_flags & OF_VDISK_FLAGS_STATE_ACTIVE)
+#define OF_VDISK_SET_ACTIVE(s)                                          \
+        ((s)->vdisk_flags |= OF_VDISK_FLAGS_STATE_ACTIVE)
+#define OF_VDISK_RESET_ACTIVE(s)                                        \
+        ((s)->vdisk_flags &= ~OF_VDISK_FLAGS_STATE_ACTIVE)
+
+#define OF_VDISK_FAILED(s)                                              \
+        ((s)->vdisk_flags & OF_VDISK_FLAGS_STATE_FAILED)
+#define OF_VDISK_SET_FAILED(s)                                          \
+        ((s)->vdisk_flags |= OF_VDISK_FLAGS_STATE_FAILED)
+#define OF_VDISK_RESET_FAILED(s)                                        \
+        ((s)->vdisk_flags &= ~OF_VDISK_FLAGS_STATE_FAILED)
+
+#define OF_VDISK_IOFAILOVER_IN_PROGRESS(s)                              \
+        ((s)->vdisk_flags & OF_VDISK_FLAGS_IOFAILOVER_IN_PROGRESS)
+#define OF_VDISK_SET_IOFAILOVER_IN_PROGRESS(s)                          \
+        ((s)->vdisk_flags |= OF_VDISK_FLAGS_IOFAILOVER_IN_PROGRESS)
+#define OF_VDISK_RESET_IOFAILOVER_IN_PROGRESS(s)                        \
+        ((s)->vdisk_flags &= ~OF_VDISK_FLAGS_IOFAILOVER_IN_PROGRESS)
+
+/*
+ * VXHSAIOCB specific flags
+ */
+#define OF_ACB_QUEUED       0x00000001
+
+#define OF_AIOCB_FLAGS_QUEUED(a)            \
+        ((a)->flags & OF_ACB_QUEUED)
+#define OF_AIOCB_FLAGS_SET_QUEUED(a)        \
+        ((a)->flags |= OF_ACB_QUEUED)
+#define OF_AIOCB_FLAGS_RESET_QUEUED(a)      \
+        ((a)->flags &= ~OF_ACB_QUEUED)
+
+typedef struct qemu2qnio_ctx {
+    uint32_t            qnio_flag;
+    uint64_t            qnio_size;
+    char                *qnio_channel;
+    char                *target;
+    qnio_callback_t     qnio_cb;
+} qemu2qnio_ctx_t;
+
+typedef qemu2qnio_ctx_t qnio2qemu_ctx_t;
+
+typedef struct LibQNIOSymbol {
+        const char *name;
+        gpointer *addr;
+} LibQNIOSymbol;
+
+typedef void (*iio_cb_t) (uint32_t rfd, uint32_t reason, void *ctx,
+                          void *reply);
+
+/*
+ * HyperScale AIO callbacks structure
+ */
+typedef struct VXHSAIOCB {
+    BlockAIOCB    common;
+    size_t              ret;
+    size_t              size;
+    QEMUBH              *bh;
+    int                 aio_done;
+    int                 segments;
+    int                 flags;
+    size_t              io_offset;
+    QEMUIOVector        *qiov;
+    void                *buffer;
+    int                 direction;  /* IO direction (r/w) */
+    QSIMPLEQ_ENTRY(VXHSAIOCB) retry_entry;
+} VXHSAIOCB;
+
+typedef struct VXHSvDiskHostsInfo {
+    int     qnio_cfd;        /* Channel FD */
+    int     vdisk_rfd;      /* vDisk remote FD */
+    char    *hostip;        /* Host's IP addresses */
+    int     port;           /* Host's port number */
+} VXHSvDiskHostsInfo;
+
+/*
+ * Structure per vDisk maintained for state
+ */
+typedef struct BDRVVXHSState {
+    int                     fds[2];
+    int64_t                 vdisk_size;
+    int64_t                 vdisk_blocks;
+    int64_t                 vdisk_flags;
+    int                     vdisk_aio_count;
+    int                     event_reader_pos;
+    VXHSAIOCB             *qnio_event_acb;
+    void                    *qnio_ctx;
+    void                    *vdisk_lock; /* Lock to protect BDRVVXHSState */
+    void                    *vdisk_acb_lock;  /* Protects ACB */
+    VXHSvDiskHostsInfo    vdisk_hostinfo[MAX_HOSTS]; /* Per host info */
+    int                     vdisk_nhosts;   /* Total number of hosts */
+    int                     vdisk_cur_host_idx; /* IOs are being shipped to */
+    int                     vdisk_ask_failover_idx; /*asking permsn to ship io*/
+    QSIMPLEQ_HEAD(aio_retryq, VXHSAIOCB) vdisk_aio_retryq;
+    int                     vdisk_aio_retry_qd;
+    char                    *vdisk_guid;
+    AioContext              *aio_context;
+} BDRVVXHSState;
+
+int vxhs_load_iio_ops(void);
+void bdrv_vxhs_init(void);
+void *vxhs_initialize(void);
+void *vxhs_setup_qnio(void);
+int qemu_qnio_fini(BDRVVXHSState *s);
+void vxhs_iio_callback(uint32_t rfd, uint32_t reason, void *ctx, void *m);
+int qemu_qnio_init(BDRVVXHSState *s, const char *vxhs_uri);
+void vxhs_aio_event_reader(void *opaque);
+void vxhs_complete_aio(VXHSAIOCB *acb, BDRVVXHSState *s);
+int vxhs_aio_flush_cb(void *opaque);
+void vxhs_finish_aiocb(ssize_t ret, void *arg);
+unsigned long vxhs_get_vdisk_stat(BDRVVXHSState *s);
+int vxhs_open(BlockDriverState *bs, QDict *options,
+              int bdrv_flags, Error **errp);
+int vxhs_create(const char *filename, QemuOpts *options,
+                Error **errp);
+int vxhs_open_device(const char *vxhs_uri, int *cfd, int *rfd,
+                       BDRVVXHSState *s);
+void vxhs_close(BlockDriverState *bs);
+void vxhs_aio_cancel(BlockAIOCB *blockacb);
+int vxhs_truncate(BlockDriverState *bs, int64_t offset);
+int qemu_submit_io(BDRVVXHSState *s, struct iovec *iov, int64_t niov,
+                   int64_t offset, int cmd, qemu_aio_ctx_t acb);
+BlockAIOCB *vxhs_aio_flush(BlockDriverState *bs,
+                                   BlockCompletionFunc *cb, void *opaque);
+BlockAIOCB *vxhs_aio_pdiscard(BlockDriverState *bs, int64_t sector_num,
+                                     int nb_sectors,
+                                     BlockCompletionFunc *cb,
+                                     void *opaque);
+BlockAIOCB *vxhs_aio_readv(BlockDriverState *bs, int64_t sector_num,
+                                   QEMUIOVector *qiov, int nb_sectors,
+                                   BlockCompletionFunc *cb, void *opaque);
+BlockAIOCB *vxhs_aio_writev(BlockDriverState *bs, int64_t sector_num,
+                                    QEMUIOVector *qiov, int nb_sectors,
+                                    BlockCompletionFunc *cb,
+                                    void *opaque);
+coroutine_fn int vxhs_co_read(BlockDriverState *bs, int64_t sector_num,
+                                uint8_t *buf, int nb_sectors);
+coroutine_fn int vxhs_co_write(BlockDriverState *bs, int64_t sector_num,
+                                 const uint8_t *buf, int nb_sectors);
+int64_t vxhs_get_allocated_blocks(BlockDriverState *bs);
+BlockAIOCB *vxhs_aio_rw(BlockDriverState *bs, int64_t sector_num,
+                                QEMUIOVector *qiov, int nb_sectors,
+                                BlockCompletionFunc *cb,
+                                void *opaque, int write);
+int vxhs_co_flush(BlockDriverState *bs);
+coroutine_fn int vxhs_co_pdiscard(BlockDriverState *bs,
+                                   int64_t sector_num, int nb_sectors);
+int vxhs_has_zero_init(BlockDriverState *bs);
+int64_t vxhs_getlength(BlockDriverState *bs);
+void vxhs_inc_vdisk_iocount(void *ptr, uint32_t delta);
+void vxhs_dec_vdisk_iocount(void *ptr, uint32_t delta);
+uint32_t vxhs_get_vdisk_iocount(void *ptr);
+void vxhs_inc_acb_segment_count(void *ptr, int count);
+void vxhs_dec_acb_segment_count(void *ptr, int count);
+int vxhs_dec_and_get_acb_segment_count(void *ptr, int count);
+void vxhs_set_acb_buffer(void *ptr, void *buffer);
+int vxhs_sync_rw(BlockDriverState *bs, int64_t sector_num,
+                   const uint8_t *buf, int nb_sectors, int write);
+int vxhs_failover_io(BDRVVXHSState *s);
+int vxhs_reopen_vdisk(BDRVVXHSState *s,
+                        int hostinfo_index);
+int vxhs_switch_storage_agent(BDRVVXHSState *s);
+int vxhs_check_io_failover_ready(BDRVVXHSState *s,
+                                   int hostinfo_index);
+int vxhs_build_io_target_list(BDRVVXHSState *s, char **filenames);
+int vxhs_handle_queued_ios(BDRVVXHSState *s);
+int vxhs_restart_aio(VXHSAIOCB *acb);
+void vxhs_fail_aio(VXHSAIOCB *acb, int err);
+void vxhs_failover_ioctl_cb(int res, void *ctx);
+char *vxhs_string_iterate(char *p, const char *d, const size_t len);
+
+#endif
diff --git a/configure b/configure
index f57fcc6..c4f6261 100755
--- a/configure
+++ b/configure
@@ -320,6 +320,7 @@  vhdx=""
 numa=""
 tcmalloc="no"
 jemalloc="no"
+vxhs="yes"
 
 # parse CC options first
 for opt do
@@ -1150,6 +1151,11 @@  for opt do
   ;;
   --enable-jemalloc) jemalloc="yes"
   ;;
+  --disable-vxhs) vxhs="no"
+  ;;
+  --enable-vxhs) vxhs="yes"
+  ;;
+
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1380,6 +1386,7 @@  disabled with --disable-FEATURE, default is enabled if available:
   numa            libnuma support
   tcmalloc        tcmalloc support
   jemalloc        jemalloc support
+  vxhs            Veritas HyperScale vDisk backend support
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -4543,6 +4550,43 @@  if do_cc -nostdlib -Wl,-r -Wl,--no-relax -o $TMPMO $TMPO; then
 fi
 
 ##########################################
+# Veritas HyperScale block driver VxHS
+# Check if libqnio is installed
+if test "$vxhs" != "no" ; then
+  cat > $TMPC <<EOF
+#include <stdio.h>
+#include <qnio/qnio_api.h>
+
+void vxhs_inc_acb_segment_count(void *acb, int count);
+void vxhs_dec_acb_segment_count(void *acb, int count);
+void vxhs_set_acb_buffer(void *ptr, void *buffer);
+
+void vxhs_inc_acb_segment_count(void *ptr, int count)
+{
+}
+void vxhs_dec_acb_segment_count(void *ptr, int count)
+{
+}
+void vxhs_set_acb_buffer(void *ptr, void *buffer)
+{
+}
+int main(void) {
+    qemu_ck_initialize_lock();
+    return 0;
+}
+EOF
+  vxhs_libs="-lqnioshim -lqnio"
+  if compile_prog "" "$vxhs_libs" ; then
+    vxhs=yes
+  else
+    if test "$vxhs" = "yes" ; then
+      feature_not_found "vxhs block device" "Install libqnio. See github"
+    fi
+    vxhs=no
+  fi
+fi
+
+##########################################
 # End of CC checks
 # After here, no more $cc or $ld runs
 
@@ -5479,6 +5523,12 @@  if test "$pthread_setname_np" = "yes" ; then
   echo "CONFIG_PTHREAD_SETNAME_NP=y" >> $config_host_mak
 fi
 
+if test "$vxhs" = "yes" ; then
+  echo "CONFIG_VXHS=y" >> $config_host_mak
+  echo "VXHS_CFLAGS=$vxhs_cflags" >> $config_host_mak
+  echo "VXHS_LIBS=$vxhs_libs" >> $config_host_mak
+fi
+
 if test "$tcg_interpreter" = "yes"; then
   QEMU_INCLUDES="-I\$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
 elif test "$ARCH" = "sparc64" ; then