[v5,5/5] iotests: Add `vvfat` tests

Added several tests to verify the implementation of the vvfat driver.

We needed a way to interact with it, so created a basic `fat16.py` driver
that handled writing correct sectors for us.

Added `vvfat` to the non-generic formats, as its not a normal image format.

Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
---
 tests/qemu-iotests/check           |   2 +-
 tests/qemu-iotests/fat16.py        | 673 +++++++++++++++++++++++++++++
 tests/qemu-iotests/testenv.py      |   2 +-
 tests/qemu-iotests/tests/vvfat     | 457 ++++++++++++++++++++
 tests/qemu-iotests/tests/vvfat.out |   5 +
 5 files changed, 1137 insertions(+), 2 deletions(-)
 create mode 100644 tests/qemu-iotests/fat16.py
 create mode 100755 tests/qemu-iotests/tests/vvfat
 create mode 100755 tests/qemu-iotests/tests/vvfat.out

On Wed, Jun 12, 2024 at 08:43:26PM +0800, Amjad Alsharafi wrote:
> Added several tests to verify the implementation of the vvfat driver.
> 
> We needed a way to interact with it, so created a basic `fat16.py` driver
> that handled writing correct sectors for us.
> 
> Added `vvfat` to the non-generic formats, as its not a normal image format.
> 
> Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
> ---
>  tests/qemu-iotests/check           |   2 +-
>  tests/qemu-iotests/fat16.py        | 673 +++++++++++++++++++++++++++++
>  tests/qemu-iotests/testenv.py      |   2 +-
>  tests/qemu-iotests/tests/vvfat     | 457 ++++++++++++++++++++
>  tests/qemu-iotests/tests/vvfat.out |   5 +
>  5 files changed, 1137 insertions(+), 2 deletions(-)
>  create mode 100644 tests/qemu-iotests/fat16.py
>  create mode 100755 tests/qemu-iotests/tests/vvfat
>  create mode 100755 tests/qemu-iotests/tests/vvfat.out
> 
> 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..abe4ce1f8f
> --- /dev/null
> +++ b/tests/qemu-iotests/fat16.py
> @@ -0,0 +1,673 @@
> +# 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 List
> +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:
> +    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):
> +        """
> +        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:
> +    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 Fat16:
> +    def __init__(
> +        self,
> +        start_sector: int,
> +        size: int,
> +        sector_reader: callable,
> +        sector_writer: callable,
> +    ):
> +        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))
> +
> +        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()
> +
> +    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):
> +        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
> +            elif 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):
> +        """
> +        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):
> +        """
> +        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) -> int | None:
> +        """
> +        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")
> +        elif fat_entry == 1:
> +            raise Exception("Unexpected: RESERVED cluster")
> +        elif fat_entry >= 0xFFF8:
> +            return None
> +        elif fat_entry >= 0xFFF7:
> +            raise Exception("Invalid FAT entry")
> +        else:
> +            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):
> +        """
> +        Write the cluster at the given cluster.
> +        """
> +        assert len(data) == self.boot_sector.cluster_bytes()
> +        return self.write_sectors(
> +            self.boot_sector.first_sector_of_cluster(cluster),
> +            data,
> +        )
> +
> +    def read_directory(self, cluster: 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: int | None, name: str, ext: str, attributes: int
> +    ):
> +        """
> +        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):
> +            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):
> +        """
> +        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) -> FatDirectoryEntry | None:
> +        """
> +        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
> +            else:
> +                if current_entry.attributes & 0x10 == 0:
> +                    raise Exception(
> +                        f"{current_entry.whole_name()} is not a directory"
> +                    )
> +                else:
> +                    directory = self.read_directory(current_entry.cluster)
> +
> +    def read_file(self, entry: FatDirectoryEntry) -> 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 = 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,
> +    ):
> +        """
> +        Truncate the file at the given path to the new size.
> +        """
> +        if entry is None:
> +            return Exception("entry is None")
> +        if entry.attributes & 0x10 != 0:
> +            raise Exception(f"{entry.whole_name()} is a directory")
> +
> +        def clusters_from_size(size: 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
> +
> +        if required_clusters > current_clusters:
> +            # Allocate new clusters
> +            cluster = entry.cluster
> +            to_add = required_clusters
> +            for _ in range(current_clusters - 1):
> +                to_add -= 1
> +                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):
> +                new_cluster = self.next_free_cluster()
> +                if allocate_non_continuous:
> +                    new_cluster = self.next_free_cluster_non_continuous()
> +                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):
> +                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):
> +        """
> +        Write the content of the file at the given path.
> +        """
> +        if entry is None:
> +            return 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 = entry.cluster
> +        while cluster is not None:
> +            data_to_write = data[: self.boot_sector.cluster_bytes()]
> +            last_data = False
> +            if len(data_to_write) < self.boot_sector.cluster_bytes():
> +                last_data = True
> +                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):
> +        """
> +        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 i, 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"
> +                )
> +            else:
> +                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 588f30a4f1..4053d29de4 100644
> --- a/tests/qemu-iotests/testenv.py
> +++ b/tests/qemu-iotests/testenv.py
> @@ -250,7 +250,7 @@ def __init__(self, source_dir: str, build_dir: str,
>          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..aee5dfb3e2
> --- /dev/null
> +++ b/tests/qemu-iotests/tests/vvfat
> @@ -0,0 +1,457 @@
> +#!/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, 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):
> +    def setUp(self) -> None:
> +        if os.path.exists(filesystem):
> +            if os.path.isdir(filesystem):
> +                shutil.rmtree(filesystem)
> +            else:
> +                print(f"Error: {filesystem} exists and is not a directory")
> +                exit(1)
> +        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") 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):
> +        """
> +        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)
> +
> +        # 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
> -- 
> 2.45.1
> 

Btw Kevin, I'm not sure if I should add myself to the MAINTAINERS file
for the new files (fat16.py and vvfat) or not

Amjad

Am 13.06.2024 um 16:07 hat Amjad Alsharafi geschrieben:
> On Wed, Jun 12, 2024 at 08:43:26PM +0800, Amjad Alsharafi wrote:
> > Added several tests to verify the implementation of the vvfat driver.
> > 
> > We needed a way to interact with it, so created a basic `fat16.py` driver
> > that handled writing correct sectors for us.
> > 
> > Added `vvfat` to the non-generic formats, as its not a normal image format.
> > 
> > Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
> > ---
> >  tests/qemu-iotests/check           |   2 +-
> >  tests/qemu-iotests/fat16.py        | 673 +++++++++++++++++++++++++++++
> >  tests/qemu-iotests/testenv.py      |   2 +-
> >  tests/qemu-iotests/tests/vvfat     | 457 ++++++++++++++++++++
> >  tests/qemu-iotests/tests/vvfat.out |   5 +
> >  5 files changed, 1137 insertions(+), 2 deletions(-)
> >  create mode 100644 tests/qemu-iotests/fat16.py
> >  create mode 100755 tests/qemu-iotests/tests/vvfat
> >  create mode 100755 tests/qemu-iotests/tests/vvfat.out
> 
> Btw Kevin, I'm not sure if I should add myself to the MAINTAINERS file
> for the new files (fat16.py and vvfat) or not

You can if you really want to, but there is no need.

Basically if you see yourself maintaining these files for a long time
instead of just contributing them now and you want to be contacted
when they are changed in the future, that's when you could consider it.
But the patches will still go through my or Hanna's tree and we already
cover all of qemu-iotests, so we don't have to have a formal
maintainership definition for these files specifically.

Kevin

Am 12.06.2024 um 14:43 hat Amjad Alsharafi geschrieben:
> Added several tests to verify the implementation of the vvfat driver.
> 
> We needed a way to interact with it, so created a basic `fat16.py` driver
> that handled writing correct sectors for us.
> 
> Added `vvfat` to the non-generic formats, as its not a normal image format.
> 
> Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>

> +    def truncate_file(
> +        self,
> +        entry: FatDirectoryEntry,
> +        new_size: int,
> +        allocate_non_continuous: bool = False,
> +    ):
> +        """
> +        Truncate the file at the given path to the new size.
> +        """
> +        if entry is None:
> +            return Exception("entry is None")
> +        if entry.attributes & 0x10 != 0:
> +            raise Exception(f"{entry.whole_name()} is a directory")
> +
> +        def clusters_from_size(size: 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
> +
> +        if required_clusters > current_clusters:
> +            # Allocate new clusters
> +            cluster = entry.cluster
> +            to_add = required_clusters
> +            for _ in range(current_clusters - 1):
> +                to_add -= 1
> +                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):
> +                new_cluster = self.next_free_cluster()
> +                if allocate_non_continuous:
> +                    new_cluster = self.next_free_cluster_non_continuous()

The normal self.next_free_cluster() could be in an else branch. No
reason to search for a free cluster when you immediately overwrite it
anyway.

> +                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):
> +                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)

Other than this, the patch looks good to me and we seem to test all the
cases that are fixed by the previous patches.

Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Kevin Wolf <kwolf@redhat.com>

Kevin