[pbs-devel] [PATCH v2 vma-to-pbs] Initial commit

[Filip Schauer <f.schauer@proxmox.com>]

Implement a tool to import VMA files into a Proxmox Backup Server

Signed-off-by: Filip Schauer <f.schauer@proxmox.com>
---
Changes since v1:
* Remove unused crates and uses
* Format the code
* Use anyhow for error handling
* Use clap for parsing arguments instead of getopts
* Fix blocks being reindexed on every read
* Make sure ProxmoxBackupHandle is dropped properly on error
* Move image_chunk_buffer from stack to heap
* Move the block_index in VmaReader to the heap completely
* Initialize vectors with `Vec::with_capacity` and `resize` instead of
  the `vec!` macro, to potentially improve performance on debug builds.
* Add comments to code filling the MD5 sum field with zeros
* Change device_id arguments to usize
* Handle devices that have a size that is not aligned to 4096 properly
  in read_device_contents, when the caller provides a buffer that would
  exceed the device size.
* Avoid unnecessary loop iterations in read_device_contents when the
  buffer size is not aligned to 65536

 .cargo/config                  |   5 +
 .gitmodules                    |   6 +
 Cargo.toml                     |  18 ++
 Makefile                       |  70 +++++++
 src/main.rs                    | 311 ++++++++++++++++++++++++++++++
 src/vma.rs                     | 340 +++++++++++++++++++++++++++++++++
 submodules/proxmox             |   1 +
 submodules/proxmox-backup-qemu |   1 +
 8 files changed, 752 insertions(+)
 create mode 100644 .cargo/config
 create mode 100644 .gitmodules
 create mode 100644 Cargo.toml
 create mode 100644 Makefile
 create mode 100644 src/main.rs
 create mode 100644 src/vma.rs
 create mode 160000 submodules/proxmox
 create mode 160000 submodules/proxmox-backup-qemu

diff --git a/.cargo/config b/.cargo/config
new file mode 100644
index 0000000..3b5b6e4
--- /dev/null
+++ b/.cargo/config
@@ -0,0 +1,5 @@
+[source]
+[source.debian-packages]
+directory = "/usr/share/cargo/registry"
+[source.crates-io]
+replace-with = "debian-packages"
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..526f5ef
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,6 @@
+[submodule "submodules/proxmox-backup-qemu"]
+	path = submodules/proxmox-backup-qemu
+	url = git://git.proxmox.com/git/proxmox-backup-qemu.git
+[submodule "submodules/proxmox"]
+	path = submodules/proxmox
+	url = git://git.proxmox.com/git/proxmox.git
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..ecf9c03
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "vma-to-pbs"
+version = "0.0.1"
+authors = ["Filip Schauer <f.schauer@proxmox.com>"]
+edition = "2021"
+
+[dependencies]
+anyhow = "1.0"
+bincode = "1.3"
+clap = { version = "4.0.32", features = ["cargo"] }
+md5 = "0.7.0"
+scopeguard = "1.1.0"
+serde = "1.0"
+serde-big-array = "0.4.1"
+
+proxmox-backup-qemu = { path = "submodules/proxmox-backup-qemu" }
+proxmox-io = { path = "submodules/proxmox/proxmox-io" }
+proxmox-sys = { path = "submodules/proxmox/proxmox-sys" }
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..a0c841d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,70 @@
+include /usr/share/dpkg/default.mk
+
+PACKAGE = proxmox-vma-to-pbs
+BUILDDIR = $(PACKAGE)-$(DEB_VERSION_UPSTREAM)
+
+ARCH := $(DEB_BUILD_ARCH)
+
+DSC=$(DEB_SOURCE)_$(DEB_VERSION).dsc
+MAIN_DEB=$(PACKAGE)_$(DEB_VERSION)_$(ARCH).deb
+OTHER_DEBS = \
+	$(PACKAGE)-dev_$(DEB_VERSION)_$(ARCH).deb \
+	$(PACKAGE)-dbgsym_$(DEB_VERSION)_$(ARCH).deb
+DEBS=$(MAIN_DEB) $(OTHER_DEBS)
+
+DESTDIR=
+
+TARGET_DIR := target/debug
+
+ifeq ($(BUILD_MODE), release)
+CARGO_BUILD_ARGS += --release
+TARGETDIR := target/release
+endif
+
+.PHONY: all build
+all: build
+
+build: $(TARGETDIR)/vma-to-pbs
+$(TARGETDIR)/vma-to-pbs: Cargo.toml src/
+	cargo build $(CARGO_BUILD_ARGS)
+
+.PHONY: install
+install: $(TARGETDIR)/vma-to-pbs
+	install -D -m 0755 $(TARGETDIR)/vma-to-pbs $(DESTDIR)/usr/bin/vma-to-pbs
+
+$(BUILDDIR): submodule
+	rm -rf $@ $@.tmp && mkdir $@.tmp
+	cp -a submodules debian Makefile .cargo Cargo.toml build.rs src $@.tmp/
+	mv $@.tmp $@
+
+submodule:
+	[ -e submodules/proxmox-backup-qemu/Cargo.toml ] || [ -e submodules/proxmox/proxmox-sys/Cargo.toml ] || git submodule update --init --recursive
+
+dsc:
+	rm -rf $(BUILDDIR) $(DSC)
+	$(MAKE) $(DSC)
+	lintian $(DSC)
+
+$(DSC): $(BUILDDIR)
+	cd $(BUILDDIR); dpkg-buildpackage -S -us -uc -d
+
+sbuild: $(DSC)
+	sbuild $<
+
+.PHONY: deb dsc
+deb: $(OTHER_DEBS)
+$(OTHER_DEBS): $(MAIN_DEB)
+$(MAIN_DEB): $(BUILDDIR)
+	cd $(BUILDDIR); dpkg-buildpackage -b -us -uc
+	lintian $(DEBS)
+
+distclean: clean
+clean:
+	cargo clean
+	rm -rf $(PACKAGE)-[0-9]*/
+	rm -r *.deb *.dsc $(DEB_SOURCE)*.tar* *.build *.buildinfo *.changes Cargo.lock
+
+.PHONY: dinstall
+dinstall: $(DEBS)
+	dpkg -i $(DEBS)
+
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..1aefd29
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,311 @@
+extern crate anyhow;
+extern crate clap;
+extern crate proxmox_backup_qemu;
+extern crate proxmox_io;
+extern crate proxmox_sys;
+extern crate scopeguard;
+
+use std::env;
+use std::ffi::{c_char, CStr, CString};
+use std::ptr;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use anyhow::{anyhow, Context, Result};
+use clap::{command, Arg, ArgAction};
+use proxmox_backup_qemu::*;
+use proxmox_sys::linux::tty;
+use scopeguard::defer;
+
+mod vma;
+use vma::*;
+
+fn backup_vma_to_pbs(
+    vma_file_path: String,
+    pbs_repository: String,
+    backup_id: String,
+    pbs_password: String,
+    keyfile: Option<String>,
+    key_password: Option<String>,
+    master_keyfile: Option<String>,
+    fingerprint: String,
+    compress: bool,
+    encrypt: bool,
+) -> Result<()> {
+    println!("VMA input file: {}", vma_file_path);
+    println!("PBS repository: {}", pbs_repository);
+    println!("PBS fingerprint: {}", fingerprint);
+    println!("compress: {}", compress);
+    println!("encrypt: {}", encrypt);
+
+    let backup_time = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs();
+    println!("backup time: {}", backup_time);
+
+    let mut pbs_err: *mut c_char = ptr::null_mut();
+
+    let pbs_repository_cstr = CString::new(pbs_repository).unwrap();
+    let backup_id_cstr = CString::new(backup_id).unwrap();
+    let pbs_password_cstr = CString::new(pbs_password).unwrap();
+    let fingerprint_cstr = CString::new(fingerprint).unwrap();
+    let keyfile_cstr = keyfile.map(|v| CString::new(v).unwrap());
+    let keyfile_ptr = keyfile_cstr.map(|v| v.as_ptr()).unwrap_or(ptr::null());
+    let key_password_cstr = key_password.map(|v| CString::new(v).unwrap());
+    let key_password_ptr = key_password_cstr.map(|v| v.as_ptr()).unwrap_or(ptr::null());
+    let master_keyfile_cstr = master_keyfile.map(|v| CString::new(v).unwrap());
+    let master_keyfile_ptr = master_keyfile_cstr.map(|v| v.as_ptr()).unwrap_or(ptr::null());
+
+    let pbs = proxmox_backup_new_ns(
+        pbs_repository_cstr.as_ptr(),
+        ptr::null(),
+        backup_id_cstr.as_ptr(),
+        backup_time,
+        PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE,
+        pbs_password_cstr.as_ptr(),
+        keyfile_ptr,
+        key_password_ptr,
+        master_keyfile_ptr,
+        true,
+        false,
+        fingerprint_cstr.as_ptr(),
+        &mut pbs_err,
+    );
+
+    defer! {
+        proxmox_backup_disconnect(pbs);
+    }
+
+    if pbs == ptr::null_mut() {
+        unsafe {
+            let pbs_err_cstr = CStr::from_ptr(pbs_err);
+            return Err(anyhow!("proxmox_backup_new_ns failed: {pbs_err_cstr:?}"));
+        }
+    }
+
+    let connect_result = proxmox_backup_connect(pbs, &mut pbs_err);
+
+    if connect_result < 0 {
+        unsafe {
+            let pbs_err_cstr = CStr::from_ptr(pbs_err);
+            return Err(anyhow!("proxmox_backup_connect failed: {pbs_err_cstr:?}"));
+        }
+    }
+
+    let mut vma_reader = VmaReader::new(&vma_file_path)?;
+
+    // Handle configs
+    let configs = vma_reader.get_configs();
+    for (config_name, config_data) in configs {
+        println!("CFG: size: {} name: {}", config_data.len(), config_name);
+
+        let config_name_cstr = CString::new(config_name).unwrap();
+
+        if proxmox_backup_add_config(
+            pbs,
+            config_name_cstr.as_ptr(),
+            config_data.as_ptr(),
+            config_data.len() as u64,
+            &mut pbs_err,
+        ) < 0
+        {
+            unsafe {
+                let pbs_err_cstr = CStr::from_ptr(pbs_err);
+                return Err(anyhow!(
+                    "proxmox_backup_add_config failed: {pbs_err_cstr:?}"
+                ));
+            }
+        }
+    }
+
+    // Handle block devices
+    for device_id in 0..255 {
+        let device_name = match vma_reader.get_device_name(device_id) {
+            Some(x) => x,
+            None => {
+                continue;
+            }
+        };
+
+        let device_size = match vma_reader.get_device_size(device_id) {
+            Some(x) => x,
+            None => {
+                continue;
+            }
+        };
+
+        println!(
+            "DEV: dev_id={} size: {} devname: {}",
+            device_id, device_size, device_name
+        );
+
+        let device_name_cstr = CString::new(device_name).unwrap();
+        let pbs_device_id = proxmox_backup_register_image(
+            pbs,
+            device_name_cstr.as_ptr(),
+            device_size,
+            false,
+            &mut pbs_err,
+        );
+
+        if pbs_device_id < 0 {
+            unsafe {
+                let pbs_err_cstr = CStr::from_ptr(pbs_err);
+                return Err(anyhow!(
+                    "proxmox_backup_register_image failed: {pbs_err_cstr:?}"
+                ));
+            }
+        }
+
+        let mut image_chunk_buffer = proxmox_io::boxed::zeroed(PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE as usize);
+        let mut bytes_transferred = 0;
+
+        while bytes_transferred < device_size {
+            let bytes_left = device_size - bytes_transferred;
+            let chunk_size = bytes_left.min(PROXMOX_BACKUP_DEFAULT_CHUNK_SIZE);
+            println!(
+                "Uploading dev_id: {} offset: {:#0X} - {:#0X}",
+                device_id,
+                bytes_transferred,
+                bytes_transferred + chunk_size
+            );
+
+            let is_zero_chunk = vma_reader
+                .read_device_contents(
+                    device_id,
+                    &mut image_chunk_buffer[0..chunk_size as usize],
+                    bytes_transferred,
+                )
+                .with_context(|| {
+                    format!(
+                        "read {} bytes at offset {} from disk {} from VMA file",
+                        chunk_size, bytes_transferred, device_id
+                    )
+                })?;
+
+            let write_data_result = proxmox_backup_write_data(
+                pbs,
+                pbs_device_id as u8,
+                if is_zero_chunk {
+                    ptr::null()
+                } else {
+                    image_chunk_buffer.as_ptr()
+                },
+                bytes_transferred,
+                chunk_size,
+                &mut pbs_err,
+            );
+
+            if write_data_result < 0 {
+                unsafe {
+                    let pbs_err_cstr = CStr::from_ptr(pbs_err);
+                    return Err(anyhow!(
+                        "proxmox_backup_write_data failed: {pbs_err_cstr:?}"
+                    ));
+                }
+            }
+
+            bytes_transferred += chunk_size;
+        }
+
+        if proxmox_backup_close_image(pbs, pbs_device_id as u8, &mut pbs_err) < 0 {
+            unsafe {
+                let pbs_err_cstr = CStr::from_ptr(pbs_err);
+                return Err(anyhow!(
+                    "proxmox_backup_close_image failed: {pbs_err_cstr:?}"
+                ));
+            }
+        }
+    }
+
+    if proxmox_backup_finish(pbs, &mut pbs_err) < 0 {
+        unsafe {
+            let pbs_err_cstr = CStr::from_ptr(pbs_err);
+            return Err(anyhow!("proxmox_backup_finish failed: {pbs_err_cstr:?}"));
+        }
+    }
+
+    Ok(())
+}
+
+fn main() -> Result<()> {
+    let matches = command!()
+        .arg(
+            Arg::new("repository")
+                .long("repository")
+                .value_name("auth_id@host:port:datastore")
+                .help("Repository URL")
+                .required(true),
+        )
+        .arg(
+            Arg::new("vmid")
+                .long("vmid")
+                .value_name("VMID")
+                .help("Backup ID")
+                .required(true),
+        )
+        .arg(
+            Arg::new("fingerprint")
+                .long("fingerprint")
+                .value_name("FINGERPRINT")
+                .help("Proxmox Backup Server Fingerprint")
+                .required(true),
+        )
+        .arg(
+            Arg::new("keyfile")
+                .long("keyfile")
+                .value_name("KEYFILE")
+                .help("Key file"),
+        )
+        .arg(
+            Arg::new("master_keyfile")
+                .long("master_keyfile")
+                .value_name("MASTER_KEYFILE")
+                .help("Master key file"),
+        )
+        .arg(
+            Arg::new("compress")
+                .long("compress")
+                .short('c')
+                .help("Compress the Backup")
+                .action(ArgAction::SetTrue),
+        )
+        .arg(
+            Arg::new("encrypt")
+                .long("encrypt")
+                .short('e')
+                .help("Encrypt the Backup")
+                .action(ArgAction::SetTrue),
+        )
+        .arg(Arg::new("vma_file"))
+        .get_matches();
+
+    let pbs_repository = matches.get_one::<String>("repository").unwrap().to_string();
+    let vmid = matches.get_one::<String>("vmid").unwrap().to_string();
+    let fingerprint = matches.get_one::<String>("fingerprint").unwrap().to_string();
+
+    let keyfile = matches.get_one::<String>("keyfile");
+    let master_keyfile = matches.get_one::<String>("master_keyfile");
+    let compress = matches.get_flag("compress");
+    let encrypt = matches.get_flag("encrypt");
+
+    let vma_file_path = matches.get_one::<String>("vma_file").unwrap().to_string();
+
+    let pbs_password = String::from_utf8(tty::read_password(&"Password: ").unwrap()).unwrap();
+    let key_password = match keyfile {
+        Some(_) => Some(String::from_utf8(tty::read_password(&"Key Password: ").unwrap()).unwrap()),
+        None => None,
+    };
+
+    backup_vma_to_pbs(
+        vma_file_path,
+        pbs_repository,
+        vmid,
+        pbs_password,
+        keyfile.cloned(),
+        key_password,
+        master_keyfile.cloned(),
+        fingerprint,
+        compress,
+        encrypt,
+    )?;
+
+    Ok(())
+}
diff --git a/src/vma.rs b/src/vma.rs
new file mode 100644
index 0000000..e2c3475
--- /dev/null
+++ b/src/vma.rs
@@ -0,0 +1,340 @@
+extern crate anyhow;
+extern crate md5;
+
+use std::collections::HashMap;
+use std::fs::File;
+use std::io::{Read, Seek, SeekFrom};
+use std::mem::size_of;
+use std::{cmp, str};
+
+use anyhow::{anyhow, Result};
+use bincode::Options;
+use serde::{Deserialize, Serialize};
+use serde_big_array::BigArray;
+
+const VMA_BLOCKS_PER_EXTENT: usize = 59;
+const VMA_MAX_CONFIGS: usize = 256;
+const VMA_MAX_DEVICES: usize = 256;
+
+#[repr(C)]
+#[derive(Serialize, Deserialize)]
+struct VmaDeviceInfoHeader {
+    pub device_name_offset: u32,
+    reserved: [u8; 4],
+    pub device_size: u64,
+    reserved1: [u8; 16],
+}
+
+#[repr(C)]
+#[derive(Serialize, Deserialize)]
+struct VmaHeader {
+    pub magic: [u8; 4],
+    pub version: u32,
+    pub uuid: [u8; 16],
+    pub ctime: u64,
+    pub md5sum: [u8; 16],
+    pub blob_buffer_offset: u32,
+    pub blob_buffer_size: u32,
+    pub header_size: u32,
+    #[serde(with = "BigArray")]
+    reserved: [u8; 1984],
+    #[serde(with = "BigArray")]
+    pub config_names: [u32; VMA_MAX_CONFIGS],
+    #[serde(with = "BigArray")]
+    pub config_data: [u32; VMA_MAX_CONFIGS],
+    reserved1: [u8; 4],
+    #[serde(with = "BigArray")]
+    pub dev_info: [VmaDeviceInfoHeader; VMA_MAX_DEVICES],
+}
+
+#[repr(C)]
+#[derive(Serialize, Deserialize)]
+struct VmaBlockInfo {
+    pub mask: u16,
+    reserved: u8,
+    pub dev_id: u8,
+    pub cluster_num: u32,
+}
+
+#[repr(C)]
+#[derive(Serialize, Deserialize)]
+struct VmaExtentHeader {
+    pub magic: [u8; 4],
+    reserved: [u8; 2],
+    pub block_count: u16,
+    pub uuid: [u8; 16],
+    pub md5sum: [u8; 16],
+    #[serde(with = "BigArray")]
+    pub blockinfo: [VmaBlockInfo; VMA_BLOCKS_PER_EXTENT],
+}
+
+#[derive(Clone)]
+struct VmaBlockIndexEntry {
+    pub cluster_file_offset: u64,
+    pub mask: u16,
+}
+
+pub struct VmaReader {
+    vma_file: File,
+    vma_header: VmaHeader,
+    configs: HashMap<String, String>,
+    block_index: Vec<Vec<VmaBlockIndexEntry>>,
+    blocks_are_indexed: bool,
+}
+
+impl VmaReader {
+    pub fn new(vma_file_path: &str) -> Result<Self> {
+        let mut vma_file = match File::open(vma_file_path) {
+            Err(why) => return Err(anyhow!("couldn't open {}: {}", vma_file_path, why)),
+            Ok(file) => file,
+        };
+
+        let vma_header = Self::read_header(&mut vma_file).unwrap();
+        let configs = Self::read_blob_buffer(&mut vma_file, &vma_header).unwrap();
+        let block_index: Vec<Vec<VmaBlockIndexEntry>> = (0..256).map(|_| Vec::new()).collect();
+
+        let instance = Self {
+            vma_file,
+            vma_header,
+            configs,
+            block_index,
+            blocks_are_indexed: false,
+        };
+
+        Ok(instance)
+    }
+
+    fn read_header(vma_file: &mut File) -> Result<VmaHeader> {
+        let mut buffer = Vec::with_capacity(size_of::<VmaHeader>());
+        buffer.resize(size_of::<VmaHeader>(), 0);
+        vma_file.read_exact(&mut buffer)?;
+
+        let bincode_options = bincode::DefaultOptions::new()
+            .with_fixint_encoding()
+            .with_big_endian();
+
+        let vma_header: VmaHeader = bincode_options.deserialize(&buffer)?;
+
+        if vma_header.magic != [b'V', b'M', b'A', 0] {
+            return Err(anyhow!("Invalid magic number"));
+        }
+
+        if vma_header.version != 1 {
+            return Err(anyhow!("Invalid VMA version {}", vma_header.version));
+        }
+
+        buffer.resize(vma_header.header_size as usize, 0);
+        vma_file.read_exact(&mut buffer[size_of::<VmaHeader>()..])?;
+
+        // Fill the MD5 sum field with zeros to compute the MD5 sum
+        buffer[32..48].fill(0);
+        let computed_md5sum: [u8; 16] = md5::compute(&buffer).into();
+
+        if vma_header.md5sum != computed_md5sum {
+            return Err(anyhow!("Wrong VMA header checksum"));
+        }
+
+        return Ok(vma_header);
+    }
+
+    fn read_string_from_file(vma_file: &mut File, file_offset: u64) -> Result<String> {
+        let mut size_bytes = [0u8; 2];
+        vma_file.seek(SeekFrom::Start(file_offset))?;
+        vma_file.read_exact(&mut size_bytes)?;
+        let size = u16::from_le_bytes(size_bytes) as usize;
+        let mut string_bytes = Vec::with_capacity(size - 1);
+        string_bytes.resize(size - 1, 0);
+        vma_file.read_exact(&mut string_bytes)?;
+        let string = str::from_utf8(&string_bytes)?;
+
+        return Ok(string.to_string());
+    }
+
+    fn read_blob_buffer(
+        vma_file: &mut File,
+        vma_header: &VmaHeader,
+    ) -> Result<HashMap<String, String>> {
+        let mut configs = HashMap::new();
+
+        for i in 0..VMA_MAX_CONFIGS {
+            let config_name_offset = vma_header.config_names[i];
+            let config_data_offset = vma_header.config_data[i];
+
+            if config_name_offset == 0 || config_data_offset == 0 {
+                continue;
+            }
+
+            let config_name_file_offset = (vma_header.blob_buffer_offset + config_name_offset) as u64;
+            let config_data_file_offset = (vma_header.blob_buffer_offset + config_data_offset) as u64;
+            let config_name = Self::read_string_from_file(vma_file, config_name_file_offset)?;
+            let config_data = Self::read_string_from_file(vma_file, config_data_file_offset)?;
+
+            configs.insert(String::from(config_name), String::from(config_data));
+        }
+
+        return Ok(configs);
+    }
+
+    pub fn get_configs(&self) -> HashMap<String, String> {
+        return self.configs.clone();
+    }
+
+    pub fn get_device_name(&mut self, device_id: usize) -> Option<String> {
+        if device_id >= VMA_MAX_DEVICES {
+            return None;
+        }
+
+        let device_name_offset = self.vma_header.dev_info[device_id].device_name_offset;
+
+        if device_name_offset == 0 {
+            return None;
+        }
+
+        let device_name_file_offset = (self.vma_header.blob_buffer_offset + device_name_offset) as u64;
+        let device_name = Self::read_string_from_file(&mut self.vma_file, device_name_file_offset).unwrap();
+
+        return Some(device_name.to_string());
+    }
+
+    pub fn get_device_size(&self, device_id: usize) -> Option<u64> {
+        if device_id >= VMA_MAX_DEVICES {
+            return None;
+        }
+
+        let dev_info = &self.vma_header.dev_info[device_id];
+
+        if dev_info.device_name_offset == 0 {
+            return None;
+        }
+
+        return Some(dev_info.device_size);
+    }
+
+    fn read_extent_header(vma_file: &mut File) -> Result<VmaExtentHeader> {
+        let mut buffer = Vec::with_capacity(size_of::<VmaExtentHeader>());
+        buffer.resize(size_of::<VmaExtentHeader>(), 0);
+        vma_file.read_exact(&mut buffer)?;
+
+        let bincode_options = bincode::DefaultOptions::new()
+            .with_fixint_encoding()
+            .with_big_endian();
+
+        let vma_extent_header: VmaExtentHeader = bincode_options.deserialize(&buffer)?;
+
+        if vma_extent_header.magic != [b'V', b'M', b'A', b'E'] {
+            return Err(anyhow!("Invalid magic number"));
+        }
+
+        // Fill the MD5 sum field with zeros to compute the MD5 sum
+        buffer[24..40].fill(0);
+        let computed_md5sum: [u8; 16] = md5::compute(&buffer).into();
+
+        if vma_extent_header.md5sum != computed_md5sum {
+            return Err(anyhow!("Wrong VMA extent header checksum"));
+        }
+
+        return Ok(vma_extent_header);
+    }
+
+    fn index_device_clusters(&mut self) -> Result<()> {
+        for device_id in 0..255 {
+            let device_size = match self.get_device_size(device_id) {
+                Some(x) => x,
+                None => {
+                    continue;
+                }
+            };
+
+            let device_cluster_count = (device_size + 4096 * 16 - 1) / (4096 * 16);
+
+            let block_index_entry_placeholder = VmaBlockIndexEntry {
+                cluster_file_offset: 0,
+                mask: 0,
+            };
+
+            self.block_index[device_id].resize(device_cluster_count as usize, block_index_entry_placeholder);
+        }
+
+        let mut file_offset = self.vma_header.header_size as u64;
+        let vma_file_size = self.vma_file.metadata()?.len();
+
+        while file_offset < vma_file_size {
+            self.vma_file.seek(SeekFrom::Start(file_offset))?;
+            let vma_extent_header = Self::read_extent_header(&mut self.vma_file)?;
+            file_offset += size_of::<VmaExtentHeader>() as u64;
+
+            for i in 0..VMA_BLOCKS_PER_EXTENT {
+                let blockinfo = &vma_extent_header.blockinfo[i];
+
+                if blockinfo.dev_id == 0 {
+                    continue;
+                }
+
+                let block_index_entry = VmaBlockIndexEntry {
+                    cluster_file_offset: file_offset,
+                    mask: blockinfo.mask,
+                };
+
+                self.block_index[blockinfo.dev_id as usize][blockinfo.cluster_num as usize] = block_index_entry;
+                file_offset += blockinfo.mask.count_ones() as u64 * 4096;
+            }
+        }
+
+        self.blocks_are_indexed = true;
+
+        return Ok(());
+    }
+
+    pub fn read_device_contents(
+        &mut self,
+        device_id: usize,
+        buffer: &mut [u8],
+        offset: u64,
+    ) -> Result<bool> {
+        if device_id >= VMA_MAX_DEVICES {
+            return Err(anyhow!("invalid device id {}", device_id));
+        }
+
+        if offset % (4096 * 16) != 0 {
+            return Err(anyhow!("offset is not aligned to 65536"));
+        }
+
+        // Make sure that the device clusters are already indexed
+        if !self.blocks_are_indexed {
+            self.index_device_clusters()?;
+        }
+
+        let this_device_block_index = &self.block_index[device_id];
+        let length = cmp::min(
+            buffer.len(),
+            this_device_block_index.len() * 4096 * 16 - offset as usize,
+        );
+        let mut buffer_offset = 0;
+        let mut buffer_is_zero = true;
+
+        while buffer_offset < length {
+            let block_index_entry = &this_device_block_index[(offset as usize + buffer_offset) / (4096 * 16)];
+            self.vma_file.seek(SeekFrom::Start(block_index_entry.cluster_file_offset))?;
+
+            for i in 0..16 {
+                if buffer_offset >= length {
+                    break;
+                }
+
+                let block_buffer_end = buffer_offset + cmp::min(length - buffer_offset, 4096);
+                let block_mask = ((block_index_entry.mask >> i) & 1) == 1;
+
+                if block_mask {
+                    self.vma_file.read_exact(&mut buffer[buffer_offset..block_buffer_end])?;
+                    buffer_is_zero = false;
+                } else {
+                    buffer[buffer_offset..block_buffer_end].fill(0);
+                }
+
+                buffer_offset += 4096;
+            }
+        }
+
+        return Ok(buffer_is_zero);
+    }
+}
diff --git a/submodules/proxmox b/submodules/proxmox
new file mode 160000
index 0000000..dc9ee73
--- /dev/null
+++ b/submodules/proxmox
@@ -0,0 +1 @@
+Subproject commit dc9ee737512fc2c7325f47b875d6c69ccf484cea
diff --git a/submodules/proxmox-backup-qemu b/submodules/proxmox-backup-qemu
new file mode 160000
index 0000000..73a09e9
--- /dev/null
+++ b/submodules/proxmox-backup-qemu
@@ -0,0 +1 @@
+Subproject commit 73a09e96720434e4aba7f876f9c6cf56bce58c2c
-- 
2.39.2