Merge tag 'for-upstream' of https://repo.or.cz/qemu/kevin into staging

Block layer patches

- scsi-block: Fix error handling with r/werror=stop
- Depend on newer clang for TSA, make WITH_GRAPH_RDLOCK_GUARD() fully
  checked, fix block-copy to add missing lock
- vvfat: Fix write bugs for large files and add iotests
- Clean up blockdev-snapshot-internal-sync doc
- Fix iotests 024 for qed

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# gpg:                issuer "kwolf@redhat.com"
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]

* tag 'for-upstream' of https://repo.or.cz/qemu/kevin:
  iotests/024: exclude 'backing file format' field from the output
  iotests: Add `vvfat` tests
  vvfat: Fix reading files with non-continuous clusters
  vvfat: Fix wrong checks for cluster mappings invariant
  vvfat: Fix usage of `info.file.offset`
  vvfat: Fix bug in writing to middle of file
  scsi-disk: Always report RESERVATION_CONFLICT to guest
  scsi-disk: Add warning comments that host_status errors take a shortcut
  scsi-block: Don't skip callback for sgio error status/driver_status
  scsi-disk: Use positive return value for status in dma_readv/writev
  block/graph-lock: Make WITH_GRAPH_RDLOCK_GUARD() fully checked
  block-copy: Fix missing graph lock
  qapi-block-core: Clean up blockdev-snapshot-internal-sync doc

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

13 files changed, 1280 insertions, 53 deletions

diff --git a/block/block-copy.c b/block/block-copy.c
index 7e3b378528..cc618e4561 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -595,7 +595,9 @@ static coroutine_fn int block_copy_task_entry(AioTask *task)
     if (s->discard_source && ret == 0) {
         int64_t nbytes =
             MIN(t->req.offset + t->req.bytes, s->len) - t->req.offset;
-        bdrv_co_pdiscard(s->source, t->req.offset, nbytes);
+        WITH_GRAPH_RDLOCK_GUARD() {
+            bdrv_co_pdiscard(s->source, t->req.offset, nbytes);
+        }
     }
 
     return ret;
diff --git a/block/vvfat.c b/block/vvfat.c
index 086fedf474..8ffe8b3b9b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1369,8 +1369,9 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
             return -1;
         vvfat_close_current_file(s);
         s->current_fd = fd;
-        s->current_mapping = mapping;
     }
+
+    s->current_mapping = mapping;
     return 0;
 }
 
@@ -1408,7 +1409,9 @@ read_cluster_directory:
 
         assert(s->current_fd);
 
-        offset=s->cluster_size*(cluster_num-s->current_mapping->begin)+s->current_mapping->info.file.offset;
+        offset = s->cluster_size *
+            ((cluster_num - s->current_mapping->begin)
+            + s->current_mapping->info.file.offset);
         if(lseek(s->current_fd, offset, SEEK_SET)!=offset)
             return -3;
         s->cluster=s->cluster_buffer;
@@ -1878,7 +1881,6 @@ get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
 
     uint32_t cluster_num = begin_of_direntry(direntry);
     uint32_t offset = 0;
-    int first_mapping_index = -1;
     mapping_t* mapping = NULL;
     const char* basename2 = NULL;
 
@@ -1929,8 +1931,9 @@ get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
                         (mapping->mode & MODE_DIRECTORY) == 0) {
 
                     /* was modified in qcow */
-                    if (offset != mapping->info.file.offset + s->cluster_size
-                            * (cluster_num - mapping->begin)) {
+                    if (offset != s->cluster_size
+                            * ((cluster_num - mapping->begin)
+                            + mapping->info.file.offset)) {
                         /* offset of this cluster in file chain has changed */
                         abort();
                         copy_it = 1;
@@ -1939,14 +1942,9 @@ get_cluster_count_for_direntry(BDRVVVFATState* s, direntry_t* direntry, const ch
 
                         if (strcmp(basename, basename2))
                             copy_it = 1;
-                        first_mapping_index = array_index(&(s->mapping), mapping);
-                    }
-
-                    if (mapping->first_mapping_index != first_mapping_index
-                            && mapping->info.file.offset > 0) {
-                        abort();
-                        copy_it = 1;
                     }
+                    assert(mapping->first_mapping_index == -1
+                            || mapping->info.file.offset > 0);
 
                     /* need to write out? */
                     if (!was_modified && is_file(direntry)) {
@@ -2404,7 +2402,7 @@ static int commit_mappings(BDRVVVFATState* s,
                         (mapping->end - mapping->begin);
             } else
                 next_mapping->info.file.offset = mapping->info.file.offset +
-                        mapping->end - mapping->begin;
+                        (mapping->end - mapping->begin);
 
             mapping = next_mapping;
         }
@@ -2525,8 +2523,9 @@ commit_one_file(BDRVVVFATState* s, int dir_index, uint32_t offset)
         return -1;
     }
 
-    for (i = s->cluster_size; i < offset; i += s->cluster_size)
+    for (i = 0; i < offset; i += s->cluster_size) {
         c = modified_fat_get(s, c);
+    }
 
     fd = qemu_open_old(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
     if (fd < 0) {
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index a67092db6a..4d94b2b816 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -65,6 +65,13 @@ OBJECT_DECLARE_TYPE(SCSIDiskState, SCSIDiskClass, SCSI_DISK_BASE)
 
 struct SCSIDiskClass {
     SCSIDeviceClass parent_class;
+    /*
+     * Callbacks receive ret == 0 for success. Errors are represented either as
+     * negative errno values, or as positive SAM status codes.
+     *
+     * Beware: For errors returned in host_status, the function may directly
+     * complete the request and never call the callback.
+     */
     DMAIOFunc       *dma_readv;
     DMAIOFunc       *dma_writev;
     bool            (*need_fua_emulation)(SCSICommand *cmd);
@@ -217,7 +224,7 @@ static bool scsi_handle_rw_error(SCSIDiskReq *r, int ret, bool acct_failed)
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
     SCSIDiskClass *sdc = (SCSIDiskClass *) object_get_class(OBJECT(s));
     SCSISense sense = SENSE_CODE(NO_SENSE);
-    int error = 0;
+    int error;
     bool req_has_sense = false;
     BlockErrorAction action;
     int status;
@@ -228,11 +235,35 @@ static bool scsi_handle_rw_error(SCSIDiskReq *r, int ret, bool acct_failed)
     } else {
         /* A passthrough command has completed with nonzero status.  */
         status = ret;
-        if (status == CHECK_CONDITION) {
+        switch (status) {
+        case CHECK_CONDITION:
             req_has_sense = true;
             error = scsi_sense_buf_to_errno(r->req.sense, sizeof(r->req.sense));
-        } else {
+            break;
+        case RESERVATION_CONFLICT:
+            /*
+             * Don't apply the error policy, always report to the guest.
+             *
+             * This is a passthrough code path, so it's not a backend error, but
+             * a response to an invalid guest request.
+             *
+             * Windows Failover Cluster validation intentionally sends invalid
+             * requests to verify that reservations work as intended. It is
+             * crucial that it sees the resulting errors.
+             *
+             * Treating a reservation conflict as a guest-side error is obvious
+             * when a pr-manager is in use. Without one, the situation is less
+             * clear, but there might be nothing that can be fixed on the host
+             * (like in the above example), and we don't want to be stuck in a
+             * loop where resuming the VM and retrying the request immediately
+             * stops it again. So always reporting is still the safer option in
+             * this case, too.
+             */
+            error = 0;
+            break;
+        default:
             error = EINVAL;
+            break;
         }
     }
 
@@ -242,8 +273,9 @@ static bool scsi_handle_rw_error(SCSIDiskReq *r, int ret, bool acct_failed)
      * are usually retried immediately, so do not post them to QMP and
      * do not account them as failed I/O.
      */
-    if (req_has_sense &&
-        scsi_sense_buf_is_guest_recoverable(r->req.sense, sizeof(r->req.sense))) {
+    if (!error || (req_has_sense &&
+                   scsi_sense_buf_is_guest_recoverable(r->req.sense,
+                                                       sizeof(r->req.sense)))) {
         action = BLOCK_ERROR_ACTION_REPORT;
         acct_failed = false;
     } else {
@@ -283,7 +315,7 @@ static bool scsi_disk_req_check_error(SCSIDiskReq *r, int ret, bool acct_failed)
         return true;
     }
 
-    if (ret < 0) {
+    if (ret != 0) {
         return scsi_handle_rw_error(r, ret, acct_failed);
     }
 
@@ -360,7 +392,7 @@ static void scsi_write_do_fua(SCSIDiskReq *r)
 static void scsi_dma_complete_noio(SCSIDiskReq *r, int ret)
 {
     assert(r->req.aiocb == NULL);
-    if (scsi_disk_req_check_error(r, ret, false)) {
+    if (scsi_disk_req_check_error(r, ret, ret > 0)) {
         goto done;
     }
 
@@ -377,6 +409,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_dma_complete(void *opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -385,9 +418,10 @@ static void scsi_dma_complete(void *opaque, int ret)
     assert(r->req.aiocb != NULL);
     r->req.aiocb = NULL;
 
+    /* ret > 0 is accounted for in scsi_disk_req_check_error() */
     if (ret < 0) {
         block_acct_failed(blk_get_stats(s->qdev.conf.blk), &r->acct);
-    } else {
+    } else if (ret == 0) {
         block_acct_done(blk_get_stats(s->qdev.conf.blk), &r->acct);
     }
     scsi_dma_complete_noio(r, ret);
@@ -403,7 +437,7 @@ static void scsi_read_complete_noio(SCSIDiskReq *r, int ret)
            qemu_get_current_aio_context());
 
     assert(r->req.aiocb == NULL);
-    if (scsi_disk_req_check_error(r, ret, false)) {
+    if (scsi_disk_req_check_error(r, ret, ret > 0)) {
         goto done;
     }
 
@@ -416,6 +450,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_read_complete(void *opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -424,9 +459,10 @@ static void scsi_read_complete(void *opaque, int ret)
     assert(r->req.aiocb != NULL);
     r->req.aiocb = NULL;
 
+    /* ret > 0 is accounted for in scsi_disk_req_check_error() */
     if (ret < 0) {
         block_acct_failed(blk_get_stats(s->qdev.conf.blk), &r->acct);
-    } else {
+    } else if (ret == 0) {
         block_acct_done(blk_get_stats(s->qdev.conf.blk), &r->acct);
         trace_scsi_disk_read_complete(r->req.tag, r->qiov.size);
     }
@@ -534,7 +570,7 @@ static void scsi_write_complete_noio(SCSIDiskReq *r, int ret)
            qemu_get_current_aio_context());
 
     assert (r->req.aiocb == NULL);
-    if (scsi_disk_req_check_error(r, ret, false)) {
+    if (scsi_disk_req_check_error(r, ret, ret > 0)) {
         goto done;
     }
 
@@ -554,6 +590,7 @@ done:
     scsi_req_unref(&r->req);
 }
 
+/* May not be called in all error cases, don't rely on cleanup here */
 static void scsi_write_complete(void * opaque, int ret)
 {
     SCSIDiskReq *r = (SCSIDiskReq *)opaque;
@@ -562,9 +599,10 @@ static void scsi_write_complete(void * opaque, int ret)
     assert (r->req.aiocb != NULL);
     r->req.aiocb = NULL;
 
+    /* ret > 0 is accounted for in scsi_disk_req_check_error() */
     if (ret < 0) {
         block_acct_failed(blk_get_stats(s->qdev.conf.blk), &r->acct);
-    } else {
+    } else if (ret == 0) {
         block_acct_done(blk_get_stats(s->qdev.conf.blk), &r->acct);
     }
     scsi_write_complete_noio(r, ret);
@@ -2814,6 +2852,7 @@ static void scsi_block_sgio_complete(void *opaque, int ret)
     sg_io_hdr_t *io_hdr = &req->io_header;
 
     if (ret == 0) {
+        /* FIXME This skips calling req->cb() and any cleanup in it */
         if (io_hdr->host_status != SCSI_HOST_OK) {
             scsi_req_complete_failed(&r->req, io_hdr->host_status);
             scsi_req_unref(&r->req);
@@ -2825,16 +2864,6 @@ static void scsi_block_sgio_complete(void *opaque, int ret)
         } else {
             ret = io_hdr->status;
         }
-
-        if (ret > 0) {
-            if (scsi_handle_rw_error(r, ret, true)) {
-                scsi_req_unref(&r->req);
-                return;
-            }
-
-            /* Ignore error.  */
-            ret = 0;
-        }
     }
 
     req->cb(req->cb_opaque, ret);
diff --git a/include/block/graph-lock.h b/include/block/graph-lock.h
index d7545e82d0..dc8d949184 100644
--- a/include/block/graph-lock.h
+++ b/include/block/graph-lock.h
@@ -209,31 +209,38 @@ typedef struct GraphLockable { } GraphLockable;
  * unlocked. TSA_ASSERT_SHARED() makes sure that the following calls know that
  * we hold the lock while unlocking is left unchecked.
  */
-static inline GraphLockable * TSA_ASSERT_SHARED(graph_lock) TSA_NO_TSA coroutine_fn
+static inline GraphLockable * TSA_ACQUIRE_SHARED(graph_lock) coroutine_fn
 graph_lockable_auto_lock(GraphLockable *x)
 {
     bdrv_graph_co_rdlock();
     return x;
 }
 
-static inline void TSA_NO_TSA coroutine_fn
-graph_lockable_auto_unlock(GraphLockable *x)
+static inline void TSA_RELEASE_SHARED(graph_lock) coroutine_fn
+graph_lockable_auto_unlock(GraphLockable **x)
 {
     bdrv_graph_co_rdunlock();
 }
 
-G_DEFINE_AUTOPTR_CLEANUP_FUNC(GraphLockable, graph_lockable_auto_unlock)
+#define GRAPH_AUTO_UNLOCK __attribute__((cleanup(graph_lockable_auto_unlock)))
 
+/*
+ * @var is only used to break the loop after the first iteration.
+ * @unlock_var can't be unlocked and then set to NULL because TSA wants the lock
+ * to be held at the start of every iteration of the loop.
+ */
 #define WITH_GRAPH_RDLOCK_GUARD_(var)                                         \
-    for (g_autoptr(GraphLockable) var = graph_lockable_auto_lock(GML_OBJ_()); \
+    for (GraphLockable *unlock_var GRAPH_AUTO_UNLOCK =                        \
+            graph_lockable_auto_lock(GML_OBJ_()),                             \
+            *var = unlock_var;                                                \
          var;                                                                 \
-         graph_lockable_auto_unlock(var), var = NULL)
+         var = NULL)
 
 #define WITH_GRAPH_RDLOCK_GUARD() \
     WITH_GRAPH_RDLOCK_GUARD_(glue(graph_lockable_auto, __COUNTER__))
 
 #define GRAPH_RDLOCK_GUARD(x)                                       \
-    g_autoptr(GraphLockable)                                        \
+    GraphLockable * GRAPH_AUTO_UNLOCK                               \
     glue(graph_lockable_auto, __COUNTER__) G_GNUC_UNUSED =          \
             graph_lockable_auto_lock(GML_OBJ_())
 
diff --git a/meson.build b/meson.build
index 97f63aa86c..c2a050b844 100644
--- a/meson.build
+++ b/meson.build
@@ -649,7 +649,19 @@ warn_flags = [
 ]
 
 if host_os != 'darwin'
-  warn_flags += ['-Wthread-safety']
+  tsa_has_cleanup = cc.compiles('''
+    struct __attribute__((capability("mutex"))) mutex {};
+    void lock(struct mutex *m) __attribute__((acquire_capability(m)));
+    void unlock(struct mutex *m) __attribute__((release_capability(m)));
+
+    void test(void) {
+      struct mutex __attribute__((cleanup(unlock))) m;
+      lock(&m);
+    }
+  ''', args: ['-Wthread-safety', '-Werror'])
+  if tsa_has_cleanup
+    warn_flags += ['-Wthread-safety']
+  endif
 endif
 
 # Set up C++ compiler flags
diff --git a/qapi/block-core.json b/qapi/block-core.json
index a1b7cdc58e..aa40d44f1d 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -6047,10 +6047,6 @@
 #
 # @name: the name of the internal snapshot to be created
 #
-# .. note:: In a transaction, if @name is empty or any snapshot
-#    matching @name exists, the operation will fail.  Only some image
-#    formats support it; for example, qcow2, and rbd.
-#
 # Since: 1.7
 ##
 { 'struct': 'BlockdevSnapshotInternal',
@@ -6071,6 +6067,9 @@
 #     - If the format of the image used does not support it,
 #       GenericError
 #
+# .. note:: Only some image formats such as qcow2 and rbd support
+#    internal snapshots.
+#
 # Since: 1.7
 #
 # .. qmp-example::
diff --git a/tests/qemu-iotests/024 b/tests/qemu-iotests/024
index 285f17e79f..b29c76e161 100755
--- a/tests/qemu-iotests/024
+++ b/tests/qemu-iotests/024
@@ -283,7 +283,7 @@ TEST_IMG=$BASE_OLD _make_test_img -b "$BASE_NEW" -F $IMGFMT \
 CLUSTER_SIZE=$(( CLUSTER_SIZE * 2 )) TEST_IMG=$OVERLAY \
     _make_test_img -b "$BASE_OLD" -F $IMGFMT $(( CLUSTER_SIZE * 6 ))
 
-TEST_IMG=$OVERLAY _img_info
+TEST_IMG=$OVERLAY _img_info | grep -v '^backing file format:'
 
 echo
 echo "Fill backing files with data"
diff --git a/tests/qemu-iotests/024.out b/tests/qemu-iotests/024.out
index e1e8eea863..3d1e31927a 100644
--- a/tests/qemu-iotests/024.out
+++ b/tests/qemu-iotests/024.out
@@ -214,7 +214,6 @@ file format: IMGFMT
 virtual size: 384 KiB (393216 bytes)
 cluster_size: 131072
 backing file: TEST_DIR/subdir/t.IMGFMT.base_old
-backing file format: IMGFMT
 
 Fill backing files with data
 
diff --git a/tests/qemu-iotests/check b/tests/qemu-iotests/check
index 56d88ca423..545f9ec7bd 100755
--- a/tests/qemu-iotests/check
+++ b/tests/qemu-iotests/check
@@ -84,7 +84,7 @@ def make_argparser() -> argparse.ArgumentParser:
     p.set_defaults(imgfmt='raw', imgproto='file')
 
     format_list = ['raw', 'bochs', 'cloop', 'parallels', 'qcow', 'qcow2',
-                   'qed', 'vdi', 'vpc', 'vhdx', 'vmdk', 'luks', 'dmg']
+                   'qed', 'vdi', 'vpc', 'vhdx', 'vmdk', 'luks', 'dmg', 'vvfat']
     g_fmt = p.add_argument_group(
         '  image format options',
         'The following options set the IMGFMT environment variable. '
diff --git a/tests/qemu-iotests/fat16.py b/tests/qemu-iotests/fat16.py
new file mode 100644
index 0000000000..7d2d052413
--- /dev/null
+++ b/tests/qemu-iotests/fat16.py
@@ -0,0 +1,690 @@
+# A simple FAT16 driver that is used to test the `vvfat` driver in QEMU.
+#
+# Copyright (C) 2024 Amjad Alsharafi <amjadsharafi10@gmail.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from typing import Callable, List, Optional, Protocol, Set
+import string
+
+SECTOR_SIZE = 512
+DIRENTRY_SIZE = 32
+ALLOWED_FILE_CHARS = set(
+    "!#$%&'()-@^_`{}~" + string.digits + string.ascii_uppercase
+)
+
+
+class MBR:
+    def __init__(self, data: bytes):
+        assert len(data) == 512
+        self.partition_table = []
+        for i in range(4):
+            partition = data[446 + i * 16 : 446 + (i + 1) * 16]
+            self.partition_table.append(
+                {
+                    "status": partition[0],
+                    "start_head": partition[1],
+                    "start_sector": partition[2] & 0x3F,
+                    "start_cylinder": ((partition[2] & 0xC0) << 2)
+                                      | partition[3],
+                    "type": partition[4],
+                    "end_head": partition[5],
+                    "end_sector": partition[6] & 0x3F,
+                    "end_cylinder": ((partition[6] & 0xC0) << 2)
+                                    | partition[7],
+                    "start_lba": int.from_bytes(partition[8:12], "little"),
+                    "size": int.from_bytes(partition[12:16], "little"),
+                }
+            )
+
+    def __str__(self):
+        return "\n".join(
+            [
+                f"{i}: {partition}"
+                for i, partition in enumerate(self.partition_table)
+            ]
+        )
+
+
+class FatBootSector:
+    # pylint: disable=too-many-instance-attributes
+    def __init__(self, data: bytes):
+        assert len(data) == 512
+        self.bytes_per_sector = int.from_bytes(data[11:13], "little")
+        self.sectors_per_cluster = data[13]
+        self.reserved_sectors = int.from_bytes(data[14:16], "little")
+        self.fat_count = data[16]
+        self.root_entries = int.from_bytes(data[17:19], "little")
+        total_sectors_16 = int.from_bytes(data[19:21], "little")
+        self.media_descriptor = data[21]
+        self.sectors_per_fat = int.from_bytes(data[22:24], "little")
+        self.sectors_per_track = int.from_bytes(data[24:26], "little")
+        self.heads = int.from_bytes(data[26:28], "little")
+        self.hidden_sectors = int.from_bytes(data[28:32], "little")
+        total_sectors_32 = int.from_bytes(data[32:36], "little")
+        assert (
+            total_sectors_16 == 0 or total_sectors_32 == 0
+        ), "Both total sectors (16 and 32) fields are non-zero"
+        self.total_sectors = total_sectors_16 or total_sectors_32
+        self.drive_number = data[36]
+        self.volume_id = int.from_bytes(data[39:43], "little")
+        self.volume_label = data[43:54].decode("ascii").strip()
+        self.fs_type = data[54:62].decode("ascii").strip()
+
+    def root_dir_start(self):
+        """
+        Calculate the start sector of the root directory.
+        """
+        return self.reserved_sectors + self.fat_count * self.sectors_per_fat
+
+    def root_dir_size(self):
+        """
+        Calculate the size of the root directory in sectors.
+        """
+        return (
+            self.root_entries * DIRENTRY_SIZE + self.bytes_per_sector - 1
+        ) // self.bytes_per_sector
+
+    def data_sector_start(self):
+        """
+        Calculate the start sector of the data region.
+        """
+        return self.root_dir_start() + self.root_dir_size()
+
+    def first_sector_of_cluster(self, cluster: int) -> int:
+        """
+        Calculate the first sector of the given cluster.
+        """
+        return (
+            self.data_sector_start() + (cluster - 2) * self.sectors_per_cluster
+        )
+
+    def cluster_bytes(self):
+        """
+        Calculate the number of bytes in a cluster.
+        """
+        return self.bytes_per_sector * self.sectors_per_cluster
+
+    def __str__(self):
+        return (
+            f"Bytes per sector: {self.bytes_per_sector}\n"
+            f"Sectors per cluster: {self.sectors_per_cluster}\n"
+            f"Reserved sectors: {self.reserved_sectors}\n"
+            f"FAT count: {self.fat_count}\n"
+            f"Root entries: {self.root_entries}\n"
+            f"Total sectors: {self.total_sectors}\n"
+            f"Media descriptor: {self.media_descriptor}\n"
+            f"Sectors per FAT: {self.sectors_per_fat}\n"
+            f"Sectors per track: {self.sectors_per_track}\n"
+            f"Heads: {self.heads}\n"
+            f"Hidden sectors: {self.hidden_sectors}\n"
+            f"Drive number: {self.drive_number}\n"
+            f"Volume ID: {self.volume_id}\n"
+            f"Volume label: {self.volume_label}\n"
+            f"FS type: {self.fs_type}\n"
+        )
+
+
+class FatDirectoryEntry:
+    # pylint: disable=too-many-instance-attributes
+    def __init__(self, data: bytes, sector: int, offset: int):
+        self.name = data[0:8].decode("ascii").strip()
+        self.ext = data[8:11].decode("ascii").strip()
+        self.attributes = data[11]
+        self.reserved = data[12]
+        self.create_time_tenth = data[13]
+        self.create_time = int.from_bytes(data[14:16], "little")
+        self.create_date = int.from_bytes(data[16:18], "little")
+        self.last_access_date = int.from_bytes(data[18:20], "little")
+        high_cluster = int.from_bytes(data[20:22], "little")
+        self.last_mod_time = int.from_bytes(data[22:24], "little")
+        self.last_mod_date = int.from_bytes(data[24:26], "little")
+        low_cluster = int.from_bytes(data[26:28], "little")
+        self.cluster = (high_cluster << 16) | low_cluster
+        self.size_bytes = int.from_bytes(data[28:32], "little")
+
+        # extra (to help write back to disk)
+        self.sector = sector
+        self.offset = offset
+
+    def as_bytes(self) -> bytes:
+        return (
+            self.name.ljust(8, " ").encode("ascii")
+            + self.ext.ljust(3, " ").encode("ascii")
+            + self.attributes.to_bytes(1, "little")
+            + self.reserved.to_bytes(1, "little")
+            + self.create_time_tenth.to_bytes(1, "little")
+            + self.create_time.to_bytes(2, "little")
+            + self.create_date.to_bytes(2, "little")
+            + self.last_access_date.to_bytes(2, "little")
+            + (self.cluster >> 16).to_bytes(2, "little")
+            + self.last_mod_time.to_bytes(2, "little")
+            + self.last_mod_date.to_bytes(2, "little")
+            + (self.cluster & 0xFFFF).to_bytes(2, "little")
+            + self.size_bytes.to_bytes(4, "little")
+        )
+
+    def whole_name(self):
+        if self.ext:
+            return f"{self.name}.{self.ext}"
+        else:
+            return self.name
+
+    def __str__(self):
+        return (
+            f"Name: {self.name}\n"
+            f"Ext: {self.ext}\n"
+            f"Attributes: {self.attributes}\n"
+            f"Reserved: {self.reserved}\n"
+            f"Create time tenth: {self.create_time_tenth}\n"
+            f"Create time: {self.create_time}\n"
+            f"Create date: {self.create_date}\n"
+            f"Last access date: {self.last_access_date}\n"
+            f"Last mod time: {self.last_mod_time}\n"
+            f"Last mod date: {self.last_mod_date}\n"
+            f"Cluster: {self.cluster}\n"
+            f"Size: {self.size_bytes}\n"
+        )
+
+    def __repr__(self):
+        # convert to dict
+        return str(vars(self))
+
+
+class SectorReader(Protocol):
+    def __call__(self, start_sector: int, num_sectors: int = 1) -> bytes: ...
+
+# pylint: disable=broad-exception-raised
+class Fat16:
+    def __init__(
+        self,
+        start_sector: int,
+        size: int,
+        sector_reader: SectorReader,
+        sector_writer: Callable[[int, bytes], None]
+    ):
+        self.start_sector = start_sector
+        self.size_in_sectors = size
+        self.sector_reader = sector_reader
+        self.sector_writer = sector_writer
+
+        self.boot_sector = FatBootSector(self.sector_reader(start_sector, 1))
+
+        fat_size_in_sectors = (
+            self.boot_sector.sectors_per_fat * self.boot_sector.fat_count
+        )
+        self.fats = self.read_sectors(
+            self.boot_sector.reserved_sectors, fat_size_in_sectors
+        )
+        self.fats_dirty_sectors: Set[int] = set()
+
+    def read_sectors(self, start_sector: int, num_sectors: int) -> bytes:
+        return self.sector_reader(start_sector + self.start_sector,
+                                  num_sectors)
+
+    def write_sectors(self, start_sector: int, data: bytes) -> None:
+        return self.sector_writer(start_sector + self.start_sector, data)
+
+    def directory_from_bytes(
+        self, data: bytes, start_sector: int
+    ) -> List[FatDirectoryEntry]:
+        """
+        Convert `bytes` into a list of `FatDirectoryEntry` objects.
+        Will ignore long file names.
+        Will stop when it encounters a 0x00 byte.
+        """
+
+        entries = []
+        for i in range(0, len(data), DIRENTRY_SIZE):
+            entry = data[i : i + DIRENTRY_SIZE]
+
+            current_sector = start_sector + (i // SECTOR_SIZE)
+            current_offset = i % SECTOR_SIZE
+
+            if entry[0] == 0:
+                break
+
+            if entry[0] == 0xE5:
+                # Deleted file
+                continue
+
+            if entry[11] & 0xF == 0xF:
+                # Long file name
+                continue
+
+            entries.append(
+                FatDirectoryEntry(entry, current_sector, current_offset)
+            )
+        return entries
+
+    def read_root_directory(self) -> List[FatDirectoryEntry]:
+        root_dir = self.read_sectors(
+            self.boot_sector.root_dir_start(), self.boot_sector.root_dir_size()
+        )
+        return self.directory_from_bytes(
+            root_dir, self.boot_sector.root_dir_start()
+        )
+
+    def read_fat_entry(self, cluster: int) -> int:
+        """
+        Read the FAT entry for the given cluster.
+        """
+        fat_offset = cluster * 2  # FAT16
+        return int.from_bytes(self.fats[fat_offset : fat_offset + 2], "little")
+
+    def write_fat_entry(self, cluster: int, value: int) -> None:
+        """
+        Write the FAT entry for the given cluster.
+        """
+        fat_offset = cluster * 2
+        self.fats = (
+            self.fats[:fat_offset]
+            + value.to_bytes(2, "little")
+            + self.fats[fat_offset + 2 :]
+        )
+        self.fats_dirty_sectors.add(fat_offset // SECTOR_SIZE)
+
+    def flush_fats(self) -> None:
+        """
+        Write the FATs back to the disk.
+        """
+        for sector in self.fats_dirty_sectors:
+            data = self.fats[sector * SECTOR_SIZE : (sector + 1) * SECTOR_SIZE]
+            sector = self.boot_sector.reserved_sectors + sector
+            self.write_sectors(sector, data)
+        self.fats_dirty_sectors = set()
+
+    def next_cluster(self, cluster: int) -> Optional[int]:
+        """
+        Get the next cluster in the chain.
+        If its `None`, then its the last cluster.
+        The function will crash if the next cluster
+        is `FREE` (unexpected) or invalid entry.
+        """
+        fat_entry = self.read_fat_entry(cluster)
+        if fat_entry == 0:
+            raise Exception("Unexpected: FREE cluster")
+        if fat_entry == 1:
+            raise Exception("Unexpected: RESERVED cluster")
+        if fat_entry >= 0xFFF8:
+            return None
+        if fat_entry >= 0xFFF7:
+            raise Exception("Invalid FAT entry")
+
+        return fat_entry
+
+    def next_free_cluster(self) -> int:
+        """
+        Find the next free cluster.
+        """
+        # simple linear search
+        for i in range(2, 0xFFFF):
+            if self.read_fat_entry(i) == 0:
+                return i
+        raise Exception("No free clusters")
+
+    def next_free_cluster_non_continuous(self) -> int:
+        """
+        Find the next free cluster, but makes sure
+        that the cluster before and after it are not allocated.
+        """
+        # simple linear search
+        before = False
+        for i in range(2, 0xFFFF):
+            if self.read_fat_entry(i) == 0:
+                if before and self.read_fat_entry(i + 1) == 0:
+                    return i
+                else:
+                    before = True
+            else:
+                before = False
+
+        raise Exception("No free clusters")
+
+    def read_cluster(self, cluster: int) -> bytes:
+        """
+        Read the cluster at the given cluster.
+        """
+        return self.read_sectors(
+            self.boot_sector.first_sector_of_cluster(cluster),
+            self.boot_sector.sectors_per_cluster,
+        )
+
+    def write_cluster(self, cluster: int, data: bytes) -> None:
+        """
+        Write the cluster at the given cluster.
+        """
+        assert len(data) == self.boot_sector.cluster_bytes()
+        self.write_sectors(
+            self.boot_sector.first_sector_of_cluster(cluster),
+            data,
+        )
+
+    def read_directory(
+        self, cluster: Optional[int]
+    ) -> List[FatDirectoryEntry]:
+        """
+        Read the directory at the given cluster.
+        """
+        entries = []
+        while cluster is not None:
+            data = self.read_cluster(cluster)
+            entries.extend(
+                self.directory_from_bytes(
+                    data, self.boot_sector.first_sector_of_cluster(cluster)
+                )
+            )
+            cluster = self.next_cluster(cluster)
+        return entries
+
+    def add_direntry(
+        self, cluster: Optional[int], name: str, ext: str, attributes: int
+    ) -> FatDirectoryEntry:
+        """
+        Add a new directory entry to the given cluster.
+        If the cluster is `None`, then it will be added to the root directory.
+        """
+
+        def find_free_entry(data: bytes) -> Optional[int]:
+            for i in range(0, len(data), DIRENTRY_SIZE):
+                entry = data[i : i + DIRENTRY_SIZE]
+                if entry[0] == 0 or entry[0] == 0xE5:
+                    return i
+            return None
+
+        assert len(name) <= 8, "Name must be 8 characters or less"
+        assert len(ext) <= 3, "Ext must be 3 characters or less"
+        assert attributes % 0x15 != 0x15, "Invalid attributes"
+
+        # initial dummy data
+        new_entry = FatDirectoryEntry(b"\0" * 32, 0, 0)
+        new_entry.name = name.ljust(8, " ")
+        new_entry.ext = ext.ljust(3, " ")
+        new_entry.attributes = attributes
+        new_entry.reserved = 0
+        new_entry.create_time_tenth = 0
+        new_entry.create_time = 0
+        new_entry.create_date = 0
+        new_entry.last_access_date = 0
+        new_entry.last_mod_time = 0
+        new_entry.last_mod_date = 0
+        new_entry.cluster = self.next_free_cluster()
+        new_entry.size_bytes = 0
+
+        # mark as EOF
+        self.write_fat_entry(new_entry.cluster, 0xFFFF)
+
+        if cluster is None:
+            for i in range(self.boot_sector.root_dir_size()):
+                sector_data = self.read_sectors(
+                    self.boot_sector.root_dir_start() + i, 1
+                )
+                offset = find_free_entry(sector_data)
+                if offset is not None:
+                    new_entry.sector = self.boot_sector.root_dir_start() + i
+                    new_entry.offset = offset
+                    self.update_direntry(new_entry)
+                    return new_entry
+        else:
+            while cluster is not None:
+                data = self.read_cluster(cluster)
+                offset = find_free_entry(data)
+                if offset is not None:
+                    new_entry.sector = (
+                        self.boot_sector.first_sector_of_cluster(cluster)
+                         + (offset // SECTOR_SIZE))
+                    new_entry.offset = offset % SECTOR_SIZE
+                    self.update_direntry(new_entry)
+                    return new_entry
+                cluster = self.next_cluster(cluster)
+
+        raise Exception("No free directory entries")
+
+    def update_direntry(self, entry: FatDirectoryEntry) -> None:
+        """
+        Write the directory entry back to the disk.
+        """
+        sector = self.read_sectors(entry.sector, 1)
+        sector = (
+            sector[: entry.offset]
+            + entry.as_bytes()
+            + sector[entry.offset + DIRENTRY_SIZE :]
+        )
+        self.write_sectors(entry.sector, sector)
+
+    def find_direntry(self, path: str) -> Optional[FatDirectoryEntry]:
+        """
+        Find the directory entry for the given path.
+        """
+        assert path[0] == "/", "Path must start with /"
+
+        path = path[1:]  # remove the leading /
+        parts = path.split("/")
+        directory = self.read_root_directory()
+
+        current_entry = None
+
+        for i, part in enumerate(parts):
+            is_last = i == len(parts) - 1
+
+            for entry in directory:
+                if entry.whole_name() == part:
+                    current_entry = entry
+                    break
+            if current_entry is None:
+                return None
+
+            if is_last:
+                return current_entry
+
+            if current_entry.attributes & 0x10 == 0:
+                raise Exception(
+                    f"{current_entry.whole_name()} is not a directory"
+                )
+
+            directory = self.read_directory(current_entry.cluster)
+
+        assert False, "Exited loop with is_last == False"
+
+    def read_file(self, entry: Optional[FatDirectoryEntry]) -> Optional[bytes]:
+        """
+        Read the content of the file at the given path.
+        """
+        if entry is None:
+            return None
+        if entry.attributes & 0x10 != 0:
+            raise Exception(f"{entry.whole_name()} is a directory")
+
+        data = b""
+        cluster: Optional[int] = entry.cluster
+        while cluster is not None and len(data) <= entry.size_bytes:
+            data += self.read_cluster(cluster)
+            cluster = self.next_cluster(cluster)
+        return data[: entry.size_bytes]
+
+    def truncate_file(
+        self,
+        entry: FatDirectoryEntry,
+        new_size: int,
+        allocate_non_continuous: bool = False,
+    ) -> None:
+        """
+        Truncate the file at the given path to the new size.
+        """
+        if entry is None:
+            raise Exception("entry is None")
+        if entry.attributes & 0x10 != 0:
+            raise Exception(f"{entry.whole_name()} is a directory")
+
+        def clusters_from_size(size: int) -> int:
+            return (
+                size + self.boot_sector.cluster_bytes() - 1
+            ) // self.boot_sector.cluster_bytes()
+
+        # First, allocate new FATs if we need to
+        required_clusters = clusters_from_size(new_size)
+        current_clusters = clusters_from_size(entry.size_bytes)
+
+        affected_clusters = set()
+
+        # Keep at least one cluster, easier to manage this way
+        if required_clusters == 0:
+            required_clusters = 1
+        if current_clusters == 0:
+            current_clusters = 1
+
+        cluster: Optional[int]
+
+        if required_clusters > current_clusters:
+            # Allocate new clusters
+            cluster = entry.cluster
+            to_add = required_clusters
+            for _ in range(current_clusters - 1):
+                to_add -= 1
+                assert cluster is not None, "Cluster is None"
+                affected_clusters.add(cluster)
+                cluster = self.next_cluster(cluster)
+            assert required_clusters > 0, "No new clusters to allocate"
+            assert cluster is not None, "Cluster is None"
+            assert (
+                self.next_cluster(cluster) is None
+            ), "Cluster is not the last cluster"
+
+            # Allocate new clusters
+            for _ in range(to_add - 1):
+                if allocate_non_continuous:
+                    new_cluster = self.next_free_cluster_non_continuous()
+                else:
+                    new_cluster = self.next_free_cluster()
+                self.write_fat_entry(cluster, new_cluster)
+                self.write_fat_entry(new_cluster, 0xFFFF)
+                cluster = new_cluster
+
+        elif required_clusters < current_clusters:
+            # Truncate the file
+            cluster = entry.cluster
+            for _ in range(required_clusters - 1):
+                assert cluster is not None, "Cluster is None"
+                cluster = self.next_cluster(cluster)
+            assert cluster is not None, "Cluster is None"
+
+            next_cluster = self.next_cluster(cluster)
+            # mark last as EOF
+            self.write_fat_entry(cluster, 0xFFFF)
+            # free the rest
+            while next_cluster is not None:
+                cluster = next_cluster
+                next_cluster = self.next_cluster(next_cluster)
+                self.write_fat_entry(cluster, 0)
+
+        self.flush_fats()
+
+        # verify number of clusters
+        cluster = entry.cluster
+        count = 0
+        while cluster is not None:
+            count += 1
+            affected_clusters.add(cluster)
+            cluster = self.next_cluster(cluster)
+        assert (
+            count == required_clusters
+        ), f"Expected {required_clusters} clusters, got {count}"
+
+        # update the size
+        entry.size_bytes = new_size
+        self.update_direntry(entry)
+
+        # trigger every affected cluster
+        for cluster in affected_clusters:
+            first_sector = self.boot_sector.first_sector_of_cluster(cluster)
+            first_sector_data = self.read_sectors(first_sector, 1)
+            self.write_sectors(first_sector, first_sector_data)
+
+    def write_file(self, entry: FatDirectoryEntry, data: bytes) -> None:
+        """
+        Write the content of the file at the given path.
+        """
+        if entry is None:
+            raise Exception("entry is None")
+        if entry.attributes & 0x10 != 0:
+            raise Exception(f"{entry.whole_name()} is a directory")
+
+        data_len = len(data)
+
+        self.truncate_file(entry, data_len)
+
+        cluster: Optional[int] = entry.cluster
+        while cluster is not None:
+            data_to_write = data[: self.boot_sector.cluster_bytes()]
+            if len(data_to_write) < self.boot_sector.cluster_bytes():
+                old_data = self.read_cluster(cluster)
+                data_to_write += old_data[len(data_to_write) :]
+
+            self.write_cluster(cluster, data_to_write)
+            data = data[self.boot_sector.cluster_bytes() :]
+            if len(data) == 0:
+                break
+            cluster = self.next_cluster(cluster)
+
+        assert (
+            len(data) == 0
+        ), "Data was not written completely, clusters missing"
+
+    def create_file(self, path: str) -> Optional[FatDirectoryEntry]:
+        """
+        Create a new file at the given path.
+        """
+        assert path[0] == "/", "Path must start with /"
+
+        path = path[1:]  # remove the leading /
+
+        parts = path.split("/")
+
+        directory_cluster = None
+        directory = self.read_root_directory()
+
+        parts, filename = parts[:-1], parts[-1]
+
+        for _, part in enumerate(parts):
+            current_entry = None
+            for entry in directory:
+                if entry.whole_name() == part:
+                    current_entry = entry
+                    break
+            if current_entry is None:
+                return None
+
+            if current_entry.attributes & 0x10 == 0:
+                raise Exception(
+                    f"{current_entry.whole_name()} is not a directory"
+                )
+
+            directory = self.read_directory(current_entry.cluster)
+            directory_cluster = current_entry.cluster
+
+        # add new entry to the directory
+
+        filename, ext = filename.split(".")
+
+        if len(ext) > 3:
+            raise Exception("Ext must be 3 characters or less")
+        if len(filename) > 8:
+            raise Exception("Name must be 8 characters or less")
+
+        for c in filename + ext:
+
+            if c not in ALLOWED_FILE_CHARS:
+                raise Exception("Invalid character in filename")
+
+        return self.add_direntry(directory_cluster, filename, ext, 0)
diff --git a/tests/qemu-iotests/testenv.py b/tests/qemu-iotests/testenv.py
index 96d69e5696..c8848f2ec2 100644
--- a/tests/qemu-iotests/testenv.py
+++ b/tests/qemu-iotests/testenv.py
@@ -255,7 +255,7 @@ class TestEnv(ContextManager['TestEnv']):
         self.qemu_img_options = os.getenv('QEMU_IMG_OPTIONS')
         self.qemu_nbd_options = os.getenv('QEMU_NBD_OPTIONS')
 
-        is_generic = self.imgfmt not in ['bochs', 'cloop', 'dmg']
+        is_generic = self.imgfmt not in ['bochs', 'cloop', 'dmg', 'vvfat']
         self.imgfmt_generic = 'true' if is_generic else 'false'
 
         self.qemu_io_options = f'--cache {self.cachemode} --aio {self.aiomode}'
diff --git a/tests/qemu-iotests/tests/vvfat b/tests/qemu-iotests/tests/vvfat
new file mode 100755
index 0000000000..acdc6ce8ff
--- /dev/null
+++ b/tests/qemu-iotests/tests/vvfat
@@ -0,0 +1,485 @@
+#!/usr/bin/env python3
+# group: rw vvfat
+#
+# Test vvfat driver implementation
+# Here, we use a simple FAT16 implementation and check the behavior of
+# the vvfat driver.
+#
+# Copyright (C) 2024 Amjad Alsharafi <amjadsharafi10@gmail.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import os
+import shutil
+import iotests
+from iotests import imgfmt, QMPTestCase
+from fat16 import MBR, Fat16, DIRENTRY_SIZE
+
+filesystem = os.path.join(iotests.test_dir, "filesystem")
+
+nbd_sock = iotests.file_path("nbd.sock", base_dir=iotests.sock_dir)
+nbd_uri = "nbd+unix:///disk?socket=" + nbd_sock
+
+SECTOR_SIZE = 512
+
+
+class TestVVFatDriver(QMPTestCase):
+    # pylint: disable=broad-exception-raised
+    def setUp(self) -> None:
+        if os.path.exists(filesystem):
+            if os.path.isdir(filesystem):
+                shutil.rmtree(filesystem)
+            else:
+                raise Exception(f"{filesystem} exists and is not a directory")
+
+        os.mkdir(filesystem)
+
+        # Add some text files to the filesystem
+        for i in range(10):
+            with open(os.path.join(filesystem, f"file{i}.txt"),
+                      "w", encoding="ascii") as f:
+                f.write(f"Hello, world! {i}\n")
+
+        # Add 2 large files, above the cluster size (8KB)
+        with open(os.path.join(filesystem, "large1.txt"), "wb") as f:
+            # write 'A' * 1KB, 'B' * 1KB, 'C' * 1KB, ...
+            for i in range(8 * 2):  # two clusters
+                f.write(bytes([0x41 + i] * 1024))
+
+        with open(os.path.join(filesystem, "large2.txt"), "wb") as f:
+            # write 'A' * 1KB, 'B' * 1KB, 'C' * 1KB, ...
+            for i in range(8 * 3):  # 3 clusters
+                f.write(bytes([0x41 + i] * 1024))
+
+        self.vm = iotests.VM()
+
+        self.vm.add_blockdev(
+            self.vm.qmp_to_opts(
+                {
+                    "driver": imgfmt,
+                    "node-name": "disk",
+                    "rw": "true",
+                    "fat-type": "16",
+                    "dir": filesystem,
+                }
+            )
+        )
+
+        self.vm.launch()
+
+        self.vm.qmp_log("block-dirty-bitmap-add", **{
+            "node": "disk",
+            "name": "bitmap0",
+        })
+
+        # attach nbd server
+        self.vm.qmp_log(
+            "nbd-server-start",
+            **{"addr": {"type": "unix", "data": {"path": nbd_sock}}},
+            filters=[],
+        )
+
+        self.vm.qmp_log(
+            "nbd-server-add",
+            **{"device": "disk", "writable": True, "bitmap": "bitmap0"},
+        )
+
+        self.qio = iotests.QemuIoInteractive("-f", "raw", nbd_uri)
+
+    def tearDown(self) -> None:
+        self.qio.close()
+        self.vm.shutdown()
+        # print(self.vm.get_log())
+        shutil.rmtree(filesystem)
+
+    def read_sectors(self, sector: int, num: int = 1) -> bytes:
+        """
+        Read `num` sectors starting from `sector` from the `disk`.
+        This uses `QemuIoInteractive` to read the sectors into `stdout` and
+        then parse the output.
+        """
+        self.assertGreater(num, 0)
+
+        # The output contains the content of the sector in hex dump format
+        # We need to extract the content from it
+        output = self.qio.cmd(
+            f"read -v {sector * SECTOR_SIZE} {num * SECTOR_SIZE}")
+
+        # Each row is 16 bytes long, and we are writing `num` sectors
+        rows = num * SECTOR_SIZE // 16
+        output_rows = output.split("\n")[:rows]
+
+        hex_content = "".join(
+            [(row.split(": ")[1]).split("  ")[0] for row in output_rows]
+        )
+        bytes_content = bytes.fromhex(hex_content)
+
+        self.assertEqual(len(bytes_content), num * SECTOR_SIZE)
+
+        return bytes_content
+
+    def write_sectors(self, sector: int, data: bytes) -> None:
+        """
+        Write `data` to the `disk` starting from `sector`.
+        This uses `QemuIoInteractive` to write the data into the disk.
+        """
+
+        self.assertGreater(len(data), 0)
+        self.assertEqual(len(data) % SECTOR_SIZE, 0)
+
+        temp_file = os.path.join(iotests.test_dir, "temp.bin")
+        with open(temp_file, "wb") as f:
+            f.write(data)
+
+        self.qio.cmd(
+            f"write -s {temp_file} {sector * SECTOR_SIZE} {len(data)}"
+        )
+
+        os.remove(temp_file)
+
+    def init_fat16(self):
+        mbr = MBR(self.read_sectors(0))
+        return Fat16(
+            mbr.partition_table[0]["start_lba"],
+            mbr.partition_table[0]["size"],
+            self.read_sectors,
+            self.write_sectors,
+        )
+
+    # Tests
+
+    def test_fat_filesystem(self):
+        """
+        Test that vvfat produce a valid FAT16 and MBR sectors
+        """
+        mbr = MBR(self.read_sectors(0))
+
+        self.assertEqual(mbr.partition_table[0]["status"], 0x80)
+        self.assertEqual(mbr.partition_table[0]["type"], 6)
+
+        fat16 = Fat16(
+            mbr.partition_table[0]["start_lba"],
+            mbr.partition_table[0]["size"],
+            self.read_sectors,
+            self.write_sectors,
+        )
+        self.assertEqual(fat16.boot_sector.bytes_per_sector, 512)
+        self.assertEqual(fat16.boot_sector.volume_label, "QEMU VVFAT")
+
+    def test_read_root_directory(self):
+        """
+        Test the content of the root directory
+        """
+        fat16 = self.init_fat16()
+
+        root_dir = fat16.read_root_directory()
+
+        self.assertEqual(len(root_dir), 13)  # 12 + 1 special file
+
+        files = {
+            "QEMU VVF.AT": 0,  # special empty file
+            "FILE0.TXT": 16,
+            "FILE1.TXT": 16,
+            "FILE2.TXT": 16,
+            "FILE3.TXT": 16,
+            "FILE4.TXT": 16,
+            "FILE5.TXT": 16,
+            "FILE6.TXT": 16,
+            "FILE7.TXT": 16,
+            "FILE8.TXT": 16,
+            "FILE9.TXT": 16,
+            "LARGE1.TXT": 0x2000 * 2,
+            "LARGE2.TXT": 0x2000 * 3,
+        }
+
+        for entry in root_dir:
+            self.assertIn(entry.whole_name(), files)
+            self.assertEqual(entry.size_bytes, files[entry.whole_name()])
+
+    def test_direntry_as_bytes(self):
+        """
+        Test if we can convert Direntry back to bytes, so that we can write it
+        back to the disk safely.
+        """
+        fat16 = self.init_fat16()
+
+        root_dir = fat16.read_root_directory()
+        first_entry_bytes = fat16.read_sectors(
+            fat16.boot_sector.root_dir_start(), 1)
+
+        # The first entry won't be deleted, so we can compare it with the first
+        # entry in the root directory
+        self.assertEqual(root_dir[0].as_bytes(),
+                         first_entry_bytes[:DIRENTRY_SIZE])
+
+    def test_read_files(self):
+        """
+        Test reading the content of the files
+        """
+        fat16 = self.init_fat16()
+
+        for i in range(10):
+            file = fat16.find_direntry(f"/FILE{i}.TXT")
+            self.assertIsNotNone(file)
+            self.assertEqual(
+                fat16.read_file(file), f"Hello, world! {i}\n".encode("ascii")
+            )
+
+        # test large files
+        large1 = fat16.find_direntry("/LARGE1.TXT")
+        with open(os.path.join(filesystem, "large1.txt"), "rb") as f:
+            self.assertEqual(fat16.read_file(large1), f.read())
+
+        large2 = fat16.find_direntry("/LARGE2.TXT")
+        self.assertIsNotNone(large2)
+        with open(os.path.join(filesystem, "large2.txt"), "rb") as f:
+            self.assertEqual(fat16.read_file(large2), f.read())
+
+    def test_write_file_same_content_direct(self):
+        """
+        Similar to `test_write_file_in_same_content`, but we write the file
+        directly clusters and thus we don't go through the modification of
+        direntry.
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/FILE0.TXT")
+        self.assertIsNotNone(file)
+
+        data = fat16.read_cluster(file.cluster)
+        fat16.write_cluster(file.cluster, data)
+
+        with open(os.path.join(filesystem, "file0.txt"), "rb") as f:
+            self.assertEqual(fat16.read_file(file), f.read())
+
+    def test_write_file_in_same_content(self):
+        """
+        Test writing the same content to the file back to it
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/FILE0.TXT")
+        self.assertIsNotNone(file)
+
+        self.assertEqual(fat16.read_file(file), b"Hello, world! 0\n")
+
+        fat16.write_file(file, b"Hello, world! 0\n")
+        self.assertEqual(fat16.read_file(file), b"Hello, world! 0\n")
+
+        with open(os.path.join(filesystem, "file0.txt"), "rb") as f:
+            self.assertEqual(f.read(), b"Hello, world! 0\n")
+
+    def test_modify_content_same_clusters(self):
+        """
+        Test modifying the content of the file without changing the number of
+        clusters
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/FILE0.TXT")
+        self.assertIsNotNone(file)
+
+        new_content = b"Hello, world! Modified\n"
+        self.assertEqual(fat16.read_file(file), b"Hello, world! 0\n")
+
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "file0.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_truncate_file_same_clusters_less(self):
+        """
+        Test truncating the file without changing number of clusters
+        Test decreasing the file size
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/FILE0.TXT")
+        self.assertIsNotNone(file)
+
+        self.assertEqual(fat16.read_file(file), b"Hello, world! 0\n")
+
+        fat16.truncate_file(file, 5)
+        new_content = fat16.read_file(file)
+        self.assertEqual(new_content, b"Hello")
+
+        with open(os.path.join(filesystem, "file0.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_truncate_file_same_clusters_more(self):
+        """
+        Test truncating the file without changing number of clusters
+        Test increase the file size
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/FILE0.TXT")
+        self.assertIsNotNone(file)
+
+        self.assertEqual(fat16.read_file(file), b"Hello, world! 0\n")
+
+        fat16.truncate_file(file, 20)
+        new_content = fat16.read_file(file)
+        self.assertIsNotNone(new_content)
+
+        # random pattern will be appended to the file, and its not always the
+        # same
+        self.assertEqual(new_content[:16], b"Hello, world! 0\n")
+        self.assertEqual(len(new_content), 20)
+
+        with open(os.path.join(filesystem, "file0.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_write_large_file(self):
+        """
+        Test writing a large file
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE1.TXT")
+        self.assertIsNotNone(file)
+
+        # The content of LARGE1 is A * 1KB, B * 1KB, C * 1KB, ..., P * 1KB
+        # Lets change it to be Z * 1KB, Y * 1KB, X * 1KB, ..., K * 1KB
+        # without changing the number of clusters or filesize
+        new_content = b"".join([bytes([0x5A - i] * 1024) for i in range(16)])
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "large1.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_truncate_file_change_clusters_less(self):
+        """
+        Test truncating a file by reducing the number of clusters
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE1.TXT")
+        self.assertIsNotNone(file)
+
+        fat16.truncate_file(file, 1)
+        self.assertEqual(fat16.read_file(file), b"A")
+
+        with open(os.path.join(filesystem, "large1.txt"), "rb") as f:
+            self.assertEqual(f.read(), b"A")
+
+    def test_write_file_change_clusters_less(self):
+        """
+        Test truncating a file by reducing the number of clusters
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE2.TXT")
+        self.assertIsNotNone(file)
+
+        new_content = b"X" * 8 * 1024 + b"Y" * 8 * 1024
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "large2.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_write_file_change_clusters_more(self):
+        """
+        Test truncating a file by increasing the number of clusters
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE2.TXT")
+        self.assertIsNotNone(file)
+
+        # from 3 clusters to 4 clusters
+        new_content = (
+            b"W" * 8 * 1024 +
+            b"X" * 8 * 1024 +
+            b"Y" * 8 * 1024 +
+            b"Z" * 8 * 1024
+        )
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "large2.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_write_file_change_clusters_more_non_contiguous_2_mappings(self):
+        """
+        Test truncating a file by increasing the number of clusters Here we
+        allocate the new clusters in a way that makes them non-contiguous so
+        that we will get 2 cluster mappings for the file
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE1.TXT")
+        self.assertIsNotNone(file)
+
+        # from 2 clusters to 3 clusters with non-contiguous allocation
+        fat16.truncate_file(file, 3 * 0x2000, allocate_non_continuous=True)
+        new_content = b"X" * 8 * 1024 + b"Y" * 8 * 1024 + b"Z" * 8 * 1024
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "large1.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_write_file_change_clusters_more_non_contiguous_3_mappings(self):
+        """
+        Test truncating a file by increasing the number of clusters Here we
+        allocate the new clusters in a way that makes them non-contiguous so
+        that we will get 3 cluster mappings for the file
+        """
+        fat16 = self.init_fat16()
+
+        file = fat16.find_direntry("/LARGE1.TXT")
+        self.assertIsNotNone(file)
+
+        # from 2 clusters to 4 clusters with non-contiguous allocation
+        fat16.truncate_file(file, 4 * 0x2000, allocate_non_continuous=True)
+        new_content = (
+            b"W" * 8 * 1024 +
+            b"X" * 8 * 1024 +
+            b"Y" * 8 * 1024 +
+            b"Z" * 8 * 1024
+        )
+        fat16.write_file(file, new_content)
+        self.assertEqual(fat16.read_file(file), new_content)
+
+        with open(os.path.join(filesystem, "large1.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    def test_create_file(self):
+        """
+        Test creating a new file
+        """
+        fat16 = self.init_fat16()
+
+        new_file = fat16.create_file("/NEWFILE.TXT")
+
+        self.assertIsNotNone(new_file)
+        self.assertEqual(new_file.size_bytes, 0)
+
+        new_content = b"Hello, world! New file\n"
+        fat16.write_file(new_file, new_content)
+        self.assertEqual(fat16.read_file(new_file), new_content)
+
+        with open(os.path.join(filesystem, "newfile.txt"), "rb") as f:
+            self.assertEqual(f.read(), new_content)
+
+    # TODO: support deleting files
+
+
+if __name__ == "__main__":
+    # This is a specific test for vvfat driver
+    iotests.main(supported_fmts=["vvfat"], supported_protocols=["file"])
diff --git a/tests/qemu-iotests/tests/vvfat.out b/tests/qemu-iotests/tests/vvfat.out
new file mode 100755
index 0000000000..b6f257674e
--- /dev/null
+++ b/tests/qemu-iotests/tests/vvfat.out
@@ -0,0 +1,5 @@
+................
+----------------------------------------------------------------------
+Ran 16 tests
+
+OK