[RFC 0/4] virtio-blk: Add support for FUA write requests

[RFC 0/4] virtio-blk: Add support for FUA write requests

[Alberto Faria]

There is a proposal to introduce virtio-blk fua write support to the virtio
spec [1], and a matching kernel RFC [2]. This series implements the proposal by
adding VIRTIO_BLK_{F,T}_OUT_FUA uapi definitions and corresponding virtio-blk,
vhost-user-blk, and vduse-blk support.

[1] https://lore.kernel.org/virtio-comment/20250507152602.3993258-1-afaria@redhat.com/
[2] https://lore.kernel.org/linux-block/20250508001951.421467-1-afaria@redhat.com/

Alberto Faria (4):
  include: Add tentative virtio-blk FUA write definitions
  virtio-blk: Add VIRTIO_BLK_T_OUT_FUA command support
  vhost-user-blk: Add VIRTIO_BLK_T_OUT_FUA command support
  vduse-blk: Add VIRTIO_BLK_T_OUT_FUA command support

 block/export/vduse-blk.c                    |  3 +-
 block/export/vhost-user-blk-server.c        |  1 +
 block/export/virtio-blk-handler.c           |  7 ++-
 contrib/vhost-user-blk/vhost-user-blk.c     | 16 ++++--
 hw/block/vhost-user-blk.c                   |  3 ++
 hw/block/virtio-blk.c                       |  2 +
 hw/core/machine.c                           |  5 +-
 hw/virtio/virtio-qmp.c                      |  2 +
 include/standard-headers/linux/virtio_blk.h |  4 ++
 tests/qtest/vhost-user-blk-test.c           | 56 +++++++++++++++++++++
 tests/qtest/virtio-blk-test.c               | 56 +++++++++++++++++++++
 11 files changed, 148 insertions(+), 7 deletions(-)

-- 
2.49.0

[RFC 1/4] include: Add tentative virtio-blk FUA write definitions

[Alberto Faria]

Signed-off-by: Alberto Faria <afaria@redhat.com>
---
 include/standard-headers/linux/virtio_blk.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/standard-headers/linux/virtio_blk.h b/include/standard-headers/linux/virtio_blk.h
index d7be3cf5e42..67a373e7967 100644
--- a/include/standard-headers/linux/virtio_blk.h
+++ b/include/standard-headers/linux/virtio_blk.h
@@ -42,6 +42,7 @@
 #define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES is supported */
 #define VIRTIO_BLK_F_SECURE_ERASE	16 /* Secure Erase is supported */
 #define VIRTIO_BLK_F_ZONED		17	/* Zoned block device */
+#define VIRTIO_BLK_F_OUT_FUA		18	/* FUA write is supported */
 
 /* Legacy feature bits */
 #ifndef VIRTIO_BLK_NO_LEGACY
@@ -204,6 +205,9 @@ struct virtio_blk_config {
 /* Reset All zones command */
 #define VIRTIO_BLK_T_ZONE_RESET_ALL 26
 
+/* FUA write command */
+#define VIRTIO_BLK_T_OUT_FUA        27
+
 #ifndef VIRTIO_BLK_NO_LEGACY
 /* Barrier before this op. */
 #define VIRTIO_BLK_T_BARRIER	0x80000000
-- 
2.49.0

[RFC 2/4] virtio-blk: Add VIRTIO_BLK_T_OUT_FUA command support

[Alberto Faria]

Signed-off-by: Alberto Faria <afaria@redhat.com>
---
 block/export/virtio-blk-handler.c |  7 ++--
 hw/block/virtio-blk.c             |  2 ++
 hw/core/machine.c                 |  4 ++-
 hw/virtio/virtio-qmp.c            |  2 ++
 tests/qtest/virtio-blk-test.c     | 56 +++++++++++++++++++++++++++++++
 5 files changed, 68 insertions(+), 3 deletions(-)

diff --git a/block/export/virtio-blk-handler.c b/block/export/virtio-blk-handler.c
index bc1cec67570..db40529fa68 100644
--- a/block/export/virtio-blk-handler.c
+++ b/block/export/virtio-blk-handler.c
@@ -169,11 +169,13 @@ int coroutine_fn virtio_blk_process_req(VirtioBlkHandler *handler,
     type = le32_to_cpu(out.type);
     switch (type & ~VIRTIO_BLK_T_BARRIER) {
     case VIRTIO_BLK_T_IN:
-    case VIRTIO_BLK_T_OUT: {
+    case VIRTIO_BLK_T_OUT:
+    case VIRTIO_BLK_T_OUT_FUA: {
         QEMUIOVector qiov;
         int64_t offset;
         ssize_t ret = 0;
         bool is_write = type & VIRTIO_BLK_T_OUT;
+        bool is_fua = type == VIRTIO_BLK_T_OUT_FUA;
         int64_t sector_num = le64_to_cpu(out.sector);
 
         if (is_write && !handler->writable) {
@@ -197,7 +199,8 @@ int coroutine_fn virtio_blk_process_req(VirtioBlkHandler *handler,
         offset = sector_num << VIRTIO_BLK_SECTOR_BITS;
 
         if (is_write) {
-            ret = blk_co_pwritev(blk, offset, qiov.size, &qiov, 0);
+            ret = blk_co_pwritev(blk, offset, qiov.size, &qiov,
+                                 is_fua ? BDRV_REQ_FUA : 0);
         } else {
             ret = blk_co_preadv(blk, offset, qiov.size, &qiov, 0);
         }
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index b54d01d3a24..611de0fa860 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -1882,6 +1882,8 @@ static const Property virtio_blk_properties[] = {
                        conf.max_discard_sectors, BDRV_REQUEST_MAX_SECTORS),
     DEFINE_PROP_UINT32("max-write-zeroes-sectors", VirtIOBlock,
                        conf.max_write_zeroes_sectors, BDRV_REQUEST_MAX_SECTORS),
+    DEFINE_PROP_BIT64("fua-write", VirtIOBlock, host_features,
+                      VIRTIO_BLK_F_OUT_FUA, true),
     DEFINE_PROP_BOOL("x-enable-wce-if-config-wce", VirtIOBlock,
                      conf.x_enable_wce_if_config_wce, true),
 };
diff --git a/hw/core/machine.c b/hw/core/machine.c
index ed01798d37c..8439b094904 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -37,7 +37,9 @@
 #include "hw/virtio/virtio-iommu.h"
 #include "audio/audio.h"
 
-GlobalProperty hw_compat_10_0[] = {};
+GlobalProperty hw_compat_10_0[] = {
+    { "virtio-blk-device", "fua-write", "false" },
+};
 const size_t hw_compat_10_0_len = G_N_ELEMENTS(hw_compat_10_0);
 
 GlobalProperty hw_compat_9_2[] = {
diff --git a/hw/virtio/virtio-qmp.c b/hw/virtio/virtio-qmp.c
index 3b6377cf0d2..9cbdd543623 100644
--- a/hw/virtio/virtio-qmp.c
+++ b/hw/virtio/virtio-qmp.c
@@ -173,6 +173,8 @@ static const qmp_virtio_feature_map_t virtio_blk_feature_map[] = {
             "VIRTIO_BLK_F_SECURE_ERASE: Secure erase supported"),
     FEATURE_ENTRY(VIRTIO_BLK_F_ZONED, \
             "VIRTIO_BLK_F_ZONED: Zoned block devices"),
+    FEATURE_ENTRY(VIRTIO_BLK_F_OUT_FUA, \
+            "VIRTIO_BLK_F_OUT_FUA: FUA write command supported"),
 #ifndef VIRTIO_BLK_NO_LEGACY
     FEATURE_ENTRY(VIRTIO_BLK_F_BARRIER, \
             "VIRTIO_BLK_F_BARRIER: Request barriers supported"),
diff --git a/tests/qtest/virtio-blk-test.c b/tests/qtest/virtio-blk-test.c
index 98c906ebb4a..a90838b8912 100644
--- a/tests/qtest/virtio-blk-test.c
+++ b/tests/qtest/virtio-blk-test.c
@@ -88,6 +88,7 @@ static uint64_t virtio_blk_request(QGuestAllocator *alloc, QVirtioDevice *d,
     switch (req->type) {
     case VIRTIO_BLK_T_IN:
     case VIRTIO_BLK_T_OUT:
+    case VIRTIO_BLK_T_OUT_FUA:
         g_assert_cmpuint(data_size % 512, ==, 0);
         break;
     case VIRTIO_BLK_T_DISCARD:
@@ -280,6 +281,61 @@ static QVirtQueue *test_basic(QVirtioDevice *dev, QGuestAllocator *alloc)
         guest_free(alloc, req_addr);
     }
 
+    if (features & (1u << VIRTIO_BLK_F_OUT_FUA)) {
+        /* FUA write and read with 3 descriptor layout */
+        /* FUA write request */
+        req.type = VIRTIO_BLK_T_OUT_FUA;
+        req.ioprio = 1;
+        req.sector = 0;
+        req.data = g_malloc0(512);
+        strcpy(req.data, "test");
+
+        req_addr = virtio_blk_request(alloc, dev, &req, 512);
+
+        g_free(req.data);
+
+        free_head = qvirtqueue_add(qts, vq, req_addr, 16, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 16, 512, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 528, 1, true, false);
+
+        qvirtqueue_kick(qts, dev, vq, free_head);
+
+        qvirtio_wait_used_elem(qts, dev, vq, free_head, NULL,
+                            QVIRTIO_BLK_TIMEOUT_US);
+        status = readb(req_addr + 528);
+        g_assert_cmpint(status, ==, 0);
+
+        guest_free(alloc, req_addr);
+
+        /* Read request */
+        req.type = VIRTIO_BLK_T_IN;
+        req.ioprio = 1;
+        req.sector = 0;
+        req.data = g_malloc0(512);
+
+        req_addr = virtio_blk_request(alloc, dev, &req, 512);
+
+        g_free(req.data);
+
+        free_head = qvirtqueue_add(qts, vq, req_addr, 16, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 16, 512, true, true);
+        qvirtqueue_add(qts, vq, req_addr + 528, 1, true, false);
+
+        qvirtqueue_kick(qts, dev, vq, free_head);
+
+        qvirtio_wait_used_elem(qts, dev, vq, free_head, NULL,
+                            QVIRTIO_BLK_TIMEOUT_US);
+        status = readb(req_addr + 528);
+        g_assert_cmpint(status, ==, 0);
+
+        data = g_malloc0(512);
+        memread(req_addr + 16, data, 512);
+        g_assert_cmpstr(data, ==, "test");
+        g_free(data);
+
+        guest_free(alloc, req_addr);
+    }
+
     if (features & (1u << VIRTIO_F_ANY_LAYOUT)) {
         /* Write and read with 2 descriptor layout */
         /* Write request */
-- 
2.49.0

Re: [RFC 2/4] virtio-blk: Add VIRTIO_BLK_T_OUT_FUA command support

[Stefan Hajnoczi]

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On Thu, May 08, 2025 at 01:24:38AM +0100, Alberto Faria wrote:
> Signed-off-by: Alberto Faria <afaria@redhat.com>
> ---
>  block/export/virtio-blk-handler.c |  7 ++--
>  hw/block/virtio-blk.c             |  2 ++
>  hw/core/machine.c                 |  4 ++-
>  hw/virtio/virtio-qmp.c            |  2 ++
>  tests/qtest/virtio-blk-test.c     | 56 +++++++++++++++++++++++++++++++
>  5 files changed, 68 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [RFC 2/4] virtio-blk: Add VIRTIO_BLK_T_OUT_FUA command support

[Alberto Faria]

On Thu, May 8, 2025 at 9:38 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
> On Thu, May 08, 2025 at 01:24:38AM +0100, Alberto Faria wrote:
> > Signed-off-by: Alberto Faria <afaria@redhat.com>
> > ---
> >  block/export/virtio-blk-handler.c |  7 ++--
> >  hw/block/virtio-blk.c             |  2 ++
> >  hw/core/machine.c                 |  4 ++-
> >  hw/virtio/virtio-qmp.c            |  2 ++
> >  tests/qtest/virtio-blk-test.c     | 56 +++++++++++++++++++++++++++++++
> >  5 files changed, 68 insertions(+), 3 deletions(-)
>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Please disregard this version of the series, it is missing several
hw/block/virtio-blk.c changes needed to actually get
VIRTIO_BLK_T_OUT_FUA working. I've sent v2 fixing this; it only
differs on patch 2/4.

Thank you,
Alberto

[RFC 3/4] vhost-user-blk: Add VIRTIO_BLK_T_OUT_FUA command support

[Alberto Faria]

Signed-off-by: Alberto Faria <afaria@redhat.com>
---
 block/export/vhost-user-blk-server.c    |  1 +
 contrib/vhost-user-blk/vhost-user-blk.c | 16 +++++--
 hw/block/vhost-user-blk.c               |  3 ++
 hw/core/machine.c                       |  1 +
 tests/qtest/vhost-user-blk-test.c       | 56 +++++++++++++++++++++++++
 5 files changed, 74 insertions(+), 3 deletions(-)

diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user-blk-server.c
index d9d2014d9b7..fad9560b219 100644
--- a/block/export/vhost-user-blk-server.c
+++ b/block/export/vhost-user-blk-server.c
@@ -125,6 +125,7 @@ static uint64_t vu_blk_get_features(VuDev *dev)
                1ull << VIRTIO_BLK_F_FLUSH |
                1ull << VIRTIO_BLK_F_DISCARD |
                1ull << VIRTIO_BLK_F_WRITE_ZEROES |
+               1ull << VIRTIO_BLK_F_OUT_FUA |
                1ull << VIRTIO_BLK_F_CONFIG_WCE |
                1ull << VIRTIO_BLK_F_MQ |
                1ull << VIRTIO_F_VERSION_1 |
diff --git a/contrib/vhost-user-blk/vhost-user-blk.c b/contrib/vhost-user-blk/vhost-user-blk.c
index 6cc18a1c04f..8d732bbe468 100644
--- a/contrib/vhost-user-blk/vhost-user-blk.c
+++ b/contrib/vhost-user-blk/vhost-user-blk.c
@@ -154,7 +154,7 @@ vub_readv(VubReq *req, struct iovec *iov, uint32_t iovcnt)
 }
 
 static ssize_t
-vub_writev(VubReq *req, struct iovec *iov, uint32_t iovcnt)
+vub_writev(VubReq *req, struct iovec *iov, uint32_t iovcnt, int flags)
 {
     VubDev *vdev_blk = req->vdev_blk;
     ssize_t rc;
@@ -271,12 +271,19 @@ static int vub_virtio_process_req(VubDev *vdev_blk,
     type = le32_to_cpu(req->out->type);
     switch (type & ~VIRTIO_BLK_T_BARRIER) {
     case VIRTIO_BLK_T_IN:
-    case VIRTIO_BLK_T_OUT: {
+    case VIRTIO_BLK_T_OUT:
+    case VIRTIO_BLK_T_OUT_FUA: {
         ssize_t ret = 0;
         bool is_write = type & VIRTIO_BLK_T_OUT;
+        int flags = 0;
         req->sector_num = le64_to_cpu(req->out->sector);
         if (is_write) {
-            ret  = vub_writev(req, &elem->out_sg[1], out_num);
+            #ifdef RWF_SYNC
+            if (type == VIRTIO_BLK_T_OUT_FUA) {
+                flags |= RWF_SYNC;
+            }
+            #endif
+            ret  = vub_writev(req, &elem->out_sg[1], out_num, flags);
         } else {
             ret = vub_readv(req, &elem->in_sg[0], in_num);
         }
@@ -379,6 +386,9 @@ vub_get_features(VuDev *dev)
                1ull << VIRTIO_BLK_F_DISCARD |
                1ull << VIRTIO_BLK_F_WRITE_ZEROES |
                #endif
+               #ifdef RWF_SYNC
+               1ull << VIRTIO_BLK_F_OUT_FUA |
+               #endif
                1ull << VIRTIO_BLK_F_CONFIG_WCE;
 
     if (vdev_blk->enable_ro) {
diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 4bb5ed299e7..988be625969 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -44,6 +44,7 @@ static const int user_feature_bits[] = {
     VIRTIO_BLK_F_CONFIG_WCE,
     VIRTIO_BLK_F_DISCARD,
     VIRTIO_BLK_F_WRITE_ZEROES,
+    VIRTIO_BLK_F_OUT_FUA,
     VIRTIO_F_VERSION_1,
     VIRTIO_RING_F_INDIRECT_DESC,
     VIRTIO_RING_F_EVENT_IDX,
@@ -581,6 +582,8 @@ static const Property vhost_user_blk_properties[] = {
                       VIRTIO_BLK_F_DISCARD, true),
     DEFINE_PROP_BIT64("write-zeroes", VHostUserBlk, parent_obj.host_features,
                       VIRTIO_BLK_F_WRITE_ZEROES, true),
+    DEFINE_PROP_BIT64("fua-write", VHostUserBlk, parent_obj.host_features,
+                      VIRTIO_BLK_F_OUT_FUA, true),
 };
 
 static void vhost_user_blk_class_init(ObjectClass *klass, const void *data)
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 8439b094904..bcf4f3423cb 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -39,6 +39,7 @@
 
 GlobalProperty hw_compat_10_0[] = {
     { "virtio-blk-device", "fua-write", "false" },
+    { "vhost-user-blk", "fua-write", "false" },
 };
 const size_t hw_compat_10_0_len = G_N_ELEMENTS(hw_compat_10_0);
 
diff --git a/tests/qtest/vhost-user-blk-test.c b/tests/qtest/vhost-user-blk-test.c
index ea90d41232e..4c68702e0b0 100644
--- a/tests/qtest/vhost-user-blk-test.c
+++ b/tests/qtest/vhost-user-blk-test.c
@@ -72,6 +72,7 @@ static uint64_t virtio_blk_request(QGuestAllocator *alloc, QVirtioDevice *d,
     switch (req->type) {
     case VIRTIO_BLK_T_IN:
     case VIRTIO_BLK_T_OUT:
+    case VIRTIO_BLK_T_OUT_FUA:
         g_assert_cmpuint(data_size % 512, ==, 0);
         break;
     case VIRTIO_BLK_T_DISCARD:
@@ -389,6 +390,61 @@ static QVirtQueue *test_basic(QVirtioDevice *dev, QGuestAllocator *alloc)
                                           VIRTIO_BLK_T_DISCARD);
     }
 
+    if (features & (1u << VIRTIO_BLK_F_OUT_FUA)) {
+        /* FUA write and read with 3 descriptor layout */
+        /* FUA write request */
+        req.type = VIRTIO_BLK_T_OUT_FUA;
+        req.ioprio = 1;
+        req.sector = 0;
+        req.data = g_malloc0(512);
+        strcpy(req.data, "test");
+
+        req_addr = virtio_blk_request(alloc, dev, &req, 512);
+
+        g_free(req.data);
+
+        free_head = qvirtqueue_add(qts, vq, req_addr, 16, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 16, 512, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 528, 1, true, false);
+
+        qvirtqueue_kick(qts, dev, vq, free_head);
+
+        qvirtio_wait_used_elem(qts, dev, vq, free_head, NULL,
+                            QVIRTIO_BLK_TIMEOUT_US);
+        status = readb(req_addr + 528);
+        g_assert_cmpint(status, ==, 0);
+
+        guest_free(alloc, req_addr);
+
+        /* Read request */
+        req.type = VIRTIO_BLK_T_IN;
+        req.ioprio = 1;
+        req.sector = 0;
+        req.data = g_malloc0(512);
+
+        req_addr = virtio_blk_request(alloc, dev, &req, 512);
+
+        g_free(req.data);
+
+        free_head = qvirtqueue_add(qts, vq, req_addr, 16, false, true);
+        qvirtqueue_add(qts, vq, req_addr + 16, 512, true, true);
+        qvirtqueue_add(qts, vq, req_addr + 528, 1, true, false);
+
+        qvirtqueue_kick(qts, dev, vq, free_head);
+
+        qvirtio_wait_used_elem(qts, dev, vq, free_head, NULL,
+                            QVIRTIO_BLK_TIMEOUT_US);
+        status = readb(req_addr + 528);
+        g_assert_cmpint(status, ==, 0);
+
+        data = g_malloc0(512);
+        qtest_memread(qts, req_addr + 16, data, 512);
+        g_assert_cmpstr(data, ==, "test");
+        g_free(data);
+
+        guest_free(alloc, req_addr);
+    }
+
     if (features & (1u << VIRTIO_F_ANY_LAYOUT)) {
         /* Write and read with 2 descriptor layout */
         /* Write request */
-- 
2.49.0

[RFC 4/4] vduse-blk: Add VIRTIO_BLK_T_OUT_FUA command support

[Alberto Faria]

Signed-off-by: Alberto Faria <afaria@redhat.com>
---
 block/export/vduse-blk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/export/vduse-blk.c b/block/export/vduse-blk.c
index bd852e538dc..36c3c0a56e6 100644
--- a/block/export/vduse-blk.c
+++ b/block/export/vduse-blk.c
@@ -329,7 +329,8 @@ static int vduse_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
                (1ULL << VIRTIO_BLK_F_BLK_SIZE) |
                (1ULL << VIRTIO_BLK_F_FLUSH) |
                (1ULL << VIRTIO_BLK_F_DISCARD) |
-               (1ULL << VIRTIO_BLK_F_WRITE_ZEROES);
+               (1ULL << VIRTIO_BLK_F_WRITE_ZEROES) |
+               (1ULL << VIRTIO_BLK_F_OUT_FUA);
 
     if (num_queues > 1) {
         features |= 1ULL << VIRTIO_BLK_F_MQ;
-- 
2.49.0