cleanup some python tests (#482)

As suggested by Thanos, replace hard-coded struct.pack() with ctypes.Structure
objects so it's much clearer what the data being constructed is.

Replace some hard-coded unpacking with code based on ctypes::from_buffer_copy(),
but in a form that allows us to "pop" a structure from a longer buffer.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

4 files changed, 183 insertions, 128 deletions

diff --git a/test/py/libvfio_user.py b/test/py/libvfio_user.py
index 9faaf83..a73c228 100644
--- a/test/py/libvfio_user.py
+++ b/test/py/libvfio_user.py
@@ -178,6 +178,18 @@ libc = c.CDLL("libc.so.6", use_errno=True)
 #
 # Structures
 #
+
+class Structure(c.Structure):
+    def __len__(self):
+        """Handy method to return length in bytes."""
+        return len(bytes(self))
+
+    @classmethod
+    def pop_from_buffer(cls, buf):
+        """"Pop a new object from the given bytes buffer."""
+        obj = cls.from_buffer_copy(buf)
+        return obj, buf[c.sizeof(obj):]
+
 class vfu_bar_t(c.Union):
     _pack_ = 1
     _fields_ = [
@@ -185,14 +197,14 @@ class vfu_bar_t(c.Union):
         ("io", c.c_int)
     ]
 
-class vfu_pci_hdr_intr_t(c.Structure):
+class vfu_pci_hdr_intr_t(Structure):
     _pack_ = 1
     _fields_ = [
         ("iline", c.c_byte),
         ("ipin", c.c_byte)
     ]
 
-class vfu_pci_hdr_t(c.Structure):
+class vfu_pci_hdr_t(Structure):
     _pack_ = 1
     _fields_ = [
         ("id", c.c_int),
@@ -217,12 +229,63 @@ class vfu_pci_hdr_t(c.Structure):
         ("mlat", c.c_byte)
     ]
 
-class iovec_t(c.Structure):
+class iovec_t(Structure):
     _fields_ = [
         ("iov_base", c.c_void_p),
         ("iov_len", c.c_int)
     ]
 
+class vfio_irq_set(Structure):
+    _fields_ = [
+        ("argsz", c.c_uint),
+        ("flags", c.c_uint),
+        ("index", c.c_uint),
+        ("start", c.c_uint),
+        ("count", c.c_uint),
+    ]
+
+class vfio_user_device_info(Structure):
+    _fields_ = [
+        ("argsz", c.c_uint),
+        ("flags", c.c_uint),
+        ("num_regions", c.c_uint),
+        ("num_irqs", c.c_uint),
+    ]
+
+class vfio_region_info(Structure):
+    _fields_ = [
+        ("argsz", c.c_uint),
+        ("flags", c.c_uint),
+        ("index", c.c_uint),
+        ("cap_offset", c.c_uint),
+        ("size", c.c_ulong),
+        ("offset", c.c_ulong),
+    ]
+
+class vfio_region_info_cap_type(Structure):
+    _fields_ = [
+        ("id", c.c_ushort),
+        ("version", c.c_ushort),
+        ("next", c.c_uint),
+        ("type", c.c_uint),
+        ("subtype", c.c_uint),
+    ]
+
+class vfio_region_info_cap_sparse_mmap(Structure):
+    _fields_ = [
+        ("id", c.c_ushort),
+        ("version", c.c_ushort),
+        ("next", c.c_uint),
+        ("nr_areas", c.c_uint),
+        ("reserved", c.c_uint),
+    ]
+
+class vfio_region_sparse_mmap_area(Structure):
+    _fields_ = [
+        ("offset", c.c_ulong),
+        ("size", c.c_ulong),
+    ]
+
 #
 # Util functions
 #
@@ -264,13 +327,6 @@ def skip(fmt, buf):
     """Return the data remaining after skipping the given elements."""
     return buf[struct.calcsize(fmt):]
 
-def unpack_prefix(fmt, fields, buf):
-    """Return a namedtuple unpacked from the start of buf, along with the
-       remaining buf if any."""
-    t = namedtuple('_', fields)
-    size = struct.calcsize(fmt)
-    return t._make(struct.unpack_from(fmt, buf)), skip(fmt, buf)
-
 def parse_json(json_str):
     """Parse JSON into an object with attributes (instead of using a dict)."""
     return json.loads(json_str, object_hook=lambda d: SimpleNamespace(**d))
@@ -372,18 +428,6 @@ def ext_cap_hdr(buf, offset):
     cap_next >>= 4
     return cap_id, cap_next
 
-def vfio_region_info(buf):
-    return unpack_prefix("IIIIQQ", "argsz flags index cap_off size offset", buf)
-
-def vfio_region_info_cap_type(buf):
-    return unpack_prefix("HHIII", "id version next type subtype", buf)
-
-def vfio_region_info_cap_sparse_mmap(buf):
-    return unpack_prefix("HHIII", "id version next nr_areas reserved", buf)
-
-def vfio_region_sparse_mmap_area(buf):
-    return unpack_prefix("QQ", "offset size", buf)
-
 #
 # Library wrappers
 #
diff --git a/test/py/test_device_get_info.py b/test/py/test_device_get_info.py
index fe44fee..a778604 100644
--- a/test/py/test_device_get_info.py
+++ b/test/py/test_device_get_info.py
@@ -59,8 +59,7 @@ def test_device_get_info():
 
     # bad argsz
 
-    # struct vfio_device_info
-    payload = struct.pack("IIII", 8, 0, 0, 0)
+    payload = vfio_user_device_info(argsz=8, flags=0, num_regions=0, num_irqs=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_INFO, size=len(payload))
     sock.send(hdr + payload)
@@ -69,7 +68,7 @@ def test_device_get_info():
 
     # valid with larger argsz
 
-    payload = struct.pack("IIII", 32, 0, 0, 0)
+    payload = vfio_user_device_info(argsz=32, flags=0, num_regions=0, num_irqs=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_INFO, size=len(payload))
     sock.send(hdr + payload)
diff --git a/test/py/test_device_get_region_info.py b/test/py/test_device_get_region_info.py
index c81d97b..4209cfb 100644
--- a/test/py/test_device_get_region_info.py
+++ b/test/py/test_device_get_region_info.py
@@ -35,6 +35,8 @@ import os
 ctx = None
 sock = None
 
+argsz = len(vfio_region_info())
+
 def test_device_get_region_info_setup():
     global ctx, sock
 
@@ -81,8 +83,9 @@ def test_device_get_region_info_short_write():
 
 def test_device_get_region_info_bad_argsz():
 
-    # struct vfio_region_info
-    payload = struct.pack("IIIIQQ", 8, 0, VFU_PCI_DEV_BAR1_REGION_IDX, 0, 0, 0)
+    payload = vfio_region_info(argsz=8, flags=0,
+                               index=VFU_PCI_DEV_BAR1_REGION_IDX, cap_offset=0,
+                               size=0, offset=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
@@ -91,7 +94,9 @@ def test_device_get_region_info_bad_argsz():
 
 def test_device_get_region_info_bad_index():
 
-    payload = struct.pack("IIIIQQ", 32, 0, VFU_PCI_DEV_NUM_REGIONS, 0, 0, 0)
+    payload = vfio_region_info(argsz=argsz, flags=0,
+                               index=VFU_PCI_DEV_NUM_REGIONS, cap_offset=0,
+                               size=0, offset=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
@@ -100,37 +105,40 @@ def test_device_get_region_info_bad_index():
 
 def test_device_get_region_info_larger_argsz():
 
-    payload = struct.pack("IIIIQQ", 32 + 8, 0, VFU_PCI_DEV_BAR1_REGION_IDX,
-                          0, 0, 0)
+    payload = vfio_region_info(argsz=argsz + 8, flags=0,
+                          index=VFU_PCI_DEV_BAR1_REGION_IDX, cap_offset=0,
+                          size=0, offset=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
     vfu_run_ctx(ctx)
     result = get_reply(sock)
 
-    assert(len(result) == 32)
+    assert(len(result) == argsz)
 
-    info, _ = vfio_region_info(result)
+    info, _ = vfio_region_info.pop_from_buffer(result)
 
-    assert info.argsz == 32
+    assert info.argsz == argsz
     assert info.flags == (VFIO_REGION_INFO_FLAG_READ |
                           VFIO_REGION_INFO_FLAG_WRITE)
     assert info.index == VFU_PCI_DEV_BAR1_REGION_IDX
-    assert info.cap_off == 0
+    assert info.cap_offset == 0
     assert info.size == 4096
     assert info.offset == 0
 
 def test_device_get_region_info_small_argsz_caps():
     global sock
 
-    payload = struct.pack("IIIIQQ", 32, 0, VFU_PCI_DEV_BAR2_REGION_IDX, 0, 0, 0)
+    payload = vfio_region_info(argsz=argsz, flags=0,
+                          index=VFU_PCI_DEV_BAR2_REGION_IDX, cap_offset=0,
+                          size=0, offset=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
     vfu_run_ctx(ctx)
     result = get_reply(sock)
 
-    info, _ = vfio_region_info(result)
+    info, _ = vfio_region_info.pop_from_buffer(result)
 
     assert info.argsz == 80
     assert info.flags == (VFIO_REGION_INFO_FLAG_READ |
@@ -138,7 +146,7 @@ def test_device_get_region_info_small_argsz_caps():
                           VFIO_REGION_INFO_FLAG_MMAP |
                           VFIO_REGION_INFO_FLAG_CAPS)
     assert info.index == VFU_PCI_DEV_BAR2_REGION_IDX
-    assert info.cap_off == 0
+    assert info.cap_offset == 0
     assert info.size == 0x8000
     assert info.offset == 0x8000
 
@@ -150,21 +158,23 @@ def test_device_get_region_info_caps():
 
     sock = connect_client(ctx)
 
-    payload = struct.pack("IIIIQQ", 80, 0, VFU_PCI_DEV_BAR2_REGION_IDX, 0, 0, 0)
-    payload += b'\0' * (80 - 32)
+    payload = vfio_region_info(argsz=80, flags=0,
+                          index=VFU_PCI_DEV_BAR2_REGION_IDX, cap_offset=0,
+                          size=0, offset=0)
+    payload = bytes(payload) + b'\0' * (80 - 32)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
     vfu_run_ctx(ctx)
     result = get_reply(sock)
 
-    info, result = vfio_region_info(result)
-    cap, result = vfio_region_info_cap_sparse_mmap(result)
-    area1, result = vfio_region_sparse_mmap_area(result)
-    area2, result = vfio_region_sparse_mmap_area(result)
+    info, result = vfio_region_info.pop_from_buffer(result)
+    cap, result = vfio_region_info_cap_sparse_mmap.pop_from_buffer(result)
+    area1, result = vfio_region_sparse_mmap_area.pop_from_buffer(result)
+    area2, result = vfio_region_sparse_mmap_area.pop_from_buffer(result)
 
     assert info.argsz == 80
-    assert info.cap_off == 32
+    assert info.cap_offset == 32
     assert info.size == 0x8000
     assert info.offset == 0x8000
 
@@ -186,22 +196,23 @@ def test_device_get_region_info_migr():
 
     sock = connect_client(ctx)
 
-    payload = struct.pack("IIIIQQ", 80, 0, VFU_PCI_DEV_MIGR_REGION_IDX,
-                          0, 0, 0)
-    payload += b'\0' * (80 - 32)
+    payload = vfio_region_info(argsz=80, flags=0,
+                          index=VFU_PCI_DEV_MIGR_REGION_IDX, cap_offset=0,
+                          size=0, offset=0)
+    payload = bytes(payload) + b'\0' * (80 - 32)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_GET_REGION_INFO, size=len(payload))
     sock.send(hdr + payload)
     vfu_run_ctx(ctx)
     result = get_reply(sock)
 
-    info, result = vfio_region_info(result)
-    mcap, result = vfio_region_info_cap_type(result)
-    cap, result = vfio_region_info_cap_sparse_mmap(result)
-    area, result = vfio_region_sparse_mmap_area(result)
+    info, result = vfio_region_info.pop_from_buffer(result)
+    mcap, result = vfio_region_info_cap_type.pop_from_buffer(result)
+    cap, result = vfio_region_info_cap_sparse_mmap.pop_from_buffer(result)
+    area, result = vfio_region_sparse_mmap_area.pop_from_buffer(result)
 
     assert info.argsz == 80
-    assert info.cap_off == 32
+    assert info.cap_offset == 32
 
     assert mcap.id == VFIO_REGION_INFO_CAP_TYPE
     assert mcap.version == 1
diff --git a/test/py/test_device_set_irqs.py b/test/py/test_device_set_irqs.py
index 79c706e..af3a03e 100644
--- a/test/py/test_device_set_irqs.py
+++ b/test/py/test_device_set_irqs.py
@@ -36,6 +36,8 @@ import sys
 ctx = None
 sock = None
 
+argsz = len(vfio_irq_set())
+
 def test_device_set_irqs_setup():
     global ctx, sock
 
@@ -66,9 +68,9 @@ def test_device_set_irqs_short_write():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_argsz():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 3, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_REQ_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=3, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -76,9 +78,9 @@ def test_device_set_irqs_bad_argsz():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_index():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_NUM_IRQS, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_NUM_IRQS,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -86,9 +88,9 @@ def test_device_set_irqs_bad_index():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_flags_MASK_and_UNMASK():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_ACTION_UNMASK, VFU_DEV_MSIX_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_ACTION_UNMASK, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -96,10 +98,9 @@ def test_device_set_irqs_bad_flags_MASK_and_UNMASK():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_flags_DATA_NONE_and_DATA_BOOL():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE | VFIO_IRQ_SET_DATA_BOOL,
-                          VFU_DEV_MSIX_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE | VFIO_IRQ_SET_DATA_BOOL,
+                           index=VFU_DEV_MSIX_IRQ, start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -107,9 +108,9 @@ def test_device_set_irqs_bad_flags_DATA_NONE_and_DATA_BOOL():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_count_range():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 2047, 2)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=2047, count=2)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -117,9 +118,9 @@ def test_device_set_irqs_bad_start_count_range():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_count_range():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 2049, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=2049, count=1)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -127,9 +128,9 @@ def test_device_set_irqs_bad_start_count_range():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_err_irq():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_ERR_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_ERR_IRQ,
+                           start=0, count=1)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -137,9 +138,9 @@ def test_device_set_irqs_bad_action_for_err_irq():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_req_irq():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_REQ_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
+                           start=0, count=1)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -147,9 +148,9 @@ def test_device_set_irqs_bad_action_for_req_irq():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_start_for_count_0():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 1, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=1, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -157,9 +158,9 @@ def test_device_set_irqs_bad_start_for_count_0():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_for_count_0():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_MASK |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_MASK |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -167,9 +168,9 @@ def test_device_set_irqs_bad_action_for_count_0():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_action_and_data_type_for_count_0():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_BOOL, VFU_DEV_MSIX_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -177,9 +178,9 @@ def test_device_set_irqs_bad_action_and_data_type_for_count_0():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_bad_fds_for_DATA_BOOL():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_BOOL, VFU_DEV_MSIX_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=1)
 
     fd = eventfd()
 
@@ -192,9 +193,9 @@ def test_device_set_irqs_bad_fds_for_DATA_BOOL():
     os.close(fd)
 
 def test_device_set_irqs_bad_fds_for_DATA_NONE():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=1)
 
     fd = eventfd()
 
@@ -207,9 +208,9 @@ def test_device_set_irqs_bad_fds_for_DATA_NONE():
     os.close(fd)
 
 def test_device_set_irqs_bad_fds_for_count_2():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_MSIX_IRQ, 0, 2)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
 
     fd = eventfd()
 
@@ -222,18 +223,18 @@ def test_device_set_irqs_bad_fds_for_count_2():
     os.close(fd)
 
 def test_device_set_irqs_disable():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_REQ_IRQ, 0, 0)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_REQ_IRQ,
+                           start=0, count=0)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
     vfu_run_ctx(ctx)
     get_reply(sock)
 
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_REQ_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_REQ_IRQ,
+                           start=0, count=1)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -241,9 +242,9 @@ def test_device_set_irqs_disable():
     get_reply(sock)
 
 def test_device_set_irqs_enable():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_MSIX_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=1)
 
     fd = eventfd()
 
@@ -254,10 +255,10 @@ def test_device_set_irqs_enable():
     get_reply(sock)
 
 def test_device_set_irqs_trigger_bool_too_small():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII?", 21, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_BOOL, VFU_DEV_MSIX_IRQ, 0, 2,
-                          False)
+    payload = vfio_irq_set(argsz=argsz + 1, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
+    payload = bytes(payload) + struct.pack("?", False)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -265,10 +266,10 @@ def test_device_set_irqs_trigger_bool_too_small():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_trigger_bool_too_large():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII???", 23, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_BOOL, VFU_DEV_MSIX_IRQ, 0, 2,
-                          False, False, False)
+    payload = vfio_irq_set(argsz=argsz + 3, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
+    payload = bytes(payload) + struct.pack("???", False, False, False)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -276,9 +277,9 @@ def test_device_set_irqs_trigger_bool_too_large():
     get_reply(sock, expect=errno.EINVAL)
 
 def test_device_set_irqs_enable_update():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_MSIX_IRQ, 0, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=1)
 
     fd = eventfd()
 
@@ -289,9 +290,9 @@ def test_device_set_irqs_enable_update():
     get_reply(sock)
 
 def test_device_set_irqs_enable_trigger_none():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_MSIX_IRQ, 0, 2)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
 
     fd1 = eventfd(initval=4)
     fd2 = eventfd(initval=8)
@@ -302,9 +303,9 @@ def test_device_set_irqs_enable_trigger_none():
     vfu_run_ctx(ctx)
     get_reply(sock)
 
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_NONE, VFU_DEV_MSIX_IRQ, 1, 1)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_NONE, index=VFU_DEV_MSIX_IRQ,
+                           start=1, count=1)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)
@@ -315,9 +316,9 @@ def test_device_set_irqs_enable_trigger_none():
     assert struct.unpack("Q", os.read(fd2, 8))[0] == 9
 
 def test_device_set_irqs_enable_trigger_bool():
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII", 20, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_EVENTFD, VFU_DEV_MSIX_IRQ, 0, 2)
+    payload = vfio_irq_set(argsz=argsz, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_EVENTFD, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
 
     fd1 = eventfd(initval=4)
     fd2 = eventfd(initval=8)
@@ -328,10 +329,10 @@ def test_device_set_irqs_enable_trigger_bool():
     vfu_run_ctx(ctx)
     get_reply(sock)
 
-    # struct vfio_irq_set
-    payload = struct.pack("IIIII??", 22, VFIO_IRQ_SET_ACTION_TRIGGER |
-                          VFIO_IRQ_SET_DATA_BOOL, VFU_DEV_MSIX_IRQ, 0, 2,
-                          False, True)
+    payload = vfio_irq_set(argsz=argsz + 2, flags=VFIO_IRQ_SET_ACTION_TRIGGER |
+                           VFIO_IRQ_SET_DATA_BOOL, index=VFU_DEV_MSIX_IRQ,
+                           start=0, count=2)
+    payload = bytes(payload) + struct.pack("??", False, True)
 
     hdr = vfio_user_header(VFIO_USER_DEVICE_SET_IRQS, size=len(payload))
     sock.send(hdr + payload)