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//! First sketch of NBD (Network block device) protocol support in Rust
//! API is not stable yet, obviously
//!
//! https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md
#![deny(missing_docs)]
#![forbid(unsafe_code)]
// Let's support legacy rustc
#![allow(bare_trait_objects)]
extern crate byteorder;
/// Information about an export (without name)
#[derive(Debug, Default, Hash, Eq, PartialEq, Ord, PartialOrd)]
pub struct Export<Data = ()> {
/// Size of the underlying data, in bytes
pub size: u64,
/// Tell client it's readonly
pub readonly: bool,
/// Tell that NBD_CMD_RESIZE should be supported. Not implemented in this library currently
pub resizeable: bool,
/// Tell that the exposed device has slow seeks, hence clients should use elevator algorithm
pub rotational: bool,
/// Tell that NBD_CMD_TRIM operation is supported. Not implemented in this library currently
pub send_trim: bool,
/// Tell that NBD_CMD_FLUSH may be sent
pub send_flush: bool,
/// Associated data for the export
pub data: Data,
}
fn strerror(s: &'static str) -> std::io::Result<()> {
Err(std::io::Error::new(std::io::ErrorKind::InvalidData, s))
}
// based on https://doc.rust-lang.org/src/std/io/util.rs.html#48
fn mycopy<R: ?Sized, W: ?Sized, UWO>(
reader: &mut R,
mut writer: &mut W,
buf: &mut [u8],
mut limit: usize,
before_first_write: UWO,
) -> ::std::io::Result<u64>
where
R: ::std::io::Read,
W: ::std::io::Write,
UWO: FnOnce(&mut /*dyn*/ ::std::io::Write) -> ::std::io::Result<()>,
{
let mut before_first_write = Some(before_first_write);
let mut written = 0;
loop {
let to_read = buf.len().min(limit);
let len = match reader.read(&mut buf[0..to_read]) {
Ok(0) => return Ok(written),
Ok(len) => len,
Err(ref e) if e.kind() == ::std::io::ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
if let Some(bfw) = before_first_write.take() {
bfw(&mut writer)?;
}
writer.write_all(&buf[..len])?;
written += len as u64;
//eprintln!("written={} limit={} len={}", written, limit, len);
limit -= len;
if limit == 0 {
return Ok(written);
}
}
}
/// Items for implementing NBD server
///
/// "Serialize" your Read+Write+Seek into a Read+Write socket using standard protocol.
pub mod server {
use super::consts::*;
use super::{mycopy, strerror};
use byteorder::{BigEndian as BE, ReadBytesExt, WriteBytesExt};
use std::io::{Error, Read, Result, Seek, SeekFrom, Write};
#[doc(hidden)]
pub fn oldstyle_header<W: Write>(mut c: W, size: u64, flags: u32) -> Result<()> {
c.write_all(b"NBDMAGIC")?;
c.write_all(b"\x00\x00\x42\x02\x81\x86\x12\x53")?;
c.write_u64::<BE>(size)?;
c.write_u32::<BE>(flags)?;
c.write_all(&[0; 124])?;
c.flush()?;
Ok(())
}
fn reply<IO: Write + Read>(mut c: IO, clopt: u32, rtype: u32, data: &[u8]) -> Result<()> {
c.write_u64::<BE>(0x3e889045565a9)?;
c.write_u32::<BE>(clopt)?;
c.write_u32::<BE>(rtype)?;
c.write_u32::<BE>(data.len() as u32)?;
c.write_all(data)?;
c.flush()?;
Ok(())
}
pub use super::Export;
/// Passes the requested export name to the provided callback to get the requested export
pub fn handshake<IO: Write + Read, Data, F: FnOnce(&str) -> Result<Export<Data>>>(
mut c: IO,
exports: F,
) -> Result<Data> {
//let hs_flags = NBD_FLAG_FIXED_NEWSTYLE;
let hs_flags = NBD_FLAG_FIXED_NEWSTYLE | NBD_FLAG_NO_ZEROES;
c.write_all(b"NBDMAGIC")?;
c.write_all(b"IHAVEOPT")?;
c.write_u16::<BE>(hs_flags)?;
c.flush()?;
let client_flags = c.read_u32::<BE>()?;
if client_flags != NBD_FLAG_C_FIXED_NEWSTYLE
&& client_flags != (NBD_FLAG_C_FIXED_NEWSTYLE | NBD_FLAG_C_NO_ZEROES)
{
strerror("Invalid client flag")?;
}
loop {
let client_optmagic = c.read_u64::<BE>()?;
if client_optmagic != 0x49484156454F5054 {
// IHAVEOPT
strerror("Invalid client optmagic")?;
}
let clopt = c.read_u32::<BE>()?;
let optlen = c.read_u32::<BE>()?;
if optlen > 100000 {
strerror("Suspiciously big option length")?;
}
let mut opt = vec![0; optlen as usize];
c.read_exact(&mut opt)?;
match clopt {
NBD_OPT_EXPORT_NAME => {
let export_name = std::str::from_utf8(&opt)
.map_err(|_| strerror("Non-UTF8 export name requested").unwrap_err())?;
let export = exports(export_name)?;
c.write_u64::<BE>(export.size)?;
let mut flags = NBD_FLAG_HAS_FLAGS;
if export.readonly {
flags |= NBD_FLAG_READ_ONLY
} else {
flags |= NBD_FLAG_SEND_FLUSH
};
if export.resizeable {
flags |= NBD_FLAG_SEND_RESIZE
};
if export.rotational {
flags |= NBD_FLAG_ROTATIONAL
};
if export.send_trim {
flags |= NBD_FLAG_SEND_TRIM
};
c.write_u16::<BE>(flags)?;
if client_flags & NBD_FLAG_C_NO_ZEROES == 0 {
c.write_all(&[0; 124])?;
}
c.flush()?;
return Ok(export.data);
}
NBD_OPT_ABORT => {
reply(&mut c, clopt, NBD_REP_ACK, b"")?;
strerror("Client abort")?;
}
NBD_OPT_LIST => {
if optlen != 0 {
strerror("NBD_OPT_LIST with content")?;
}
reply(&mut c, clopt, NBD_REP_SERVER, b"\x00\x00\x00\x07rustnbd")?;
reply(&mut c, clopt, NBD_REP_ACK, b"")?;
}
NBD_OPT_STARTTLS => {
strerror("TLS not supported")?;
}
NBD_OPT_INFO => {
reply(&mut c, clopt, NBD_REP_ERR_UNSUP, b"")?;
}
NBD_OPT_GO => {
reply(&mut c, clopt, NBD_REP_ERR_UNSUP, b"")?;
}
NBD_OPT_STRUCTURED_REPLY => {
reply(&mut c, clopt, NBD_REP_ERR_UNSUP, b"")?;
}
NBD_OPT_EXTENDED_HEADERS => {
reply(&mut c, clopt, NBD_REP_ERR_UNSUP, b"")?;
}
_ => {
strerror("Invalid client option type")?;
}
}
}
}
fn replyt<IO: Write>(mut c: IO, error: u32, handle: u64) -> Result<()> {
c.write_u32::<BE>(0x67446698)?;
c.write_u32::<BE>(error)?;
c.write_u64::<BE>(handle)?;
Ok(())
}
fn replyte<IO: Write>(mut c: IO, error: Error, handle: u64) -> Result<()> {
let ec = if let Some(x) = error.raw_os_error() {
if (x as u32) != 0 {
x as u32
} else {
5
}
} else {
5
};
replyt(&mut c, ec, handle)
}
/// Serve given data. If readonly, use a dummy `Write` implementation.
///
/// Should be used after `handshake`
pub fn transmission<IO, D>(mut c: IO, mut data: D) -> Result<()>
where
IO: Read + Write,
D: Read + Write + Seek,
{
let mut buf = vec![0; 65536];
loop {
let magic = c.read_u32::<BE>()?;
if magic != 0x25609513 {
strerror("Invalid request magic")?;
}
let _flags = c.read_u16::<BE>()?;
let typ = c.read_u16::<BE>()?;
let handle = c.read_u64::<BE>()?;
let offset = c.read_u64::<BE>()?;
let length = c.read_u32::<BE>()?;
//eprintln!("typ={} handle={} off={} len={}", typ, handle, offset, length);
match typ {
NBD_CMD_READ => {
if let Err(e) = data.seek(SeekFrom::Start(offset)) {
replyte(&mut c, e, handle)?;
} else {
let mut writing_in_progress = false;
let ret;
{
// a hello from old borrowck
let on_first_chunk = |c: &mut /*dyn*/ Write| {
replyt(c, 0, handle)?;
writing_in_progress = true;
Ok(())
};
ret = mycopy(
&mut data,
&mut c,
&mut buf,
length as usize,
on_first_chunk,
);
}
match ret {
Err(e) => {
if writing_in_progress {
// Reading errors after already copying first chunk
// cannot be really handled, so aborting the entire connection
return Err(e);
} else {
// Errors in the very first chunk can be non-fatal
replyte(&mut c, e, handle)?
}
}
Ok(x) if x == (length as u64) => {}
Ok(_) => {
strerror("sudden EOF")?;
}
}
}
}
NBD_CMD_WRITE => {
if let Err(e) = data.seek(SeekFrom::Start(offset)) {
replyte(&mut c, e, handle)?;
} else {
let ret = mycopy(&mut c, &mut data, &mut buf, length as usize, |_| Ok(()));
match ret {
Err(e) => replyte(&mut c, e, handle)?,
Ok(x) if x == (length as u64) => {
replyt(&mut c, 0, handle)?;
}
Ok(_) => {
strerror("sudden EOF")?;
}
}
}
}
NBD_CMD_DISC => {
return Ok(());
}
NBD_CMD_FLUSH => {
data.flush()?;
replyt(&mut c, 0, handle)?;
}
NBD_CMD_TRIM => {
replyt(&mut c, 38, handle)?;
}
NBD_CMD_WRITE_ZEROES => {
replyt(&mut c, 38, handle)?;
}
_ => strerror("Unknown command from client")?,
}
c.flush()?;
}
}
/// Recommended port for NBD servers, especially with new handshake format.
/// There is some untested, doc-hidden old handshake support in this library.
pub const DEFAULT_TCP_PORT: u16 = 10809;
} // mod server
/// Items for implementing NBD client.
///
/// Turn Read+Write into a Read+Write+Seek using a standard protocol.
pub mod client {
use super::consts::*;
use super::{strerror, CheckedAddI64, ClampToU32};
use byteorder::{BigEndian as BE, ReadBytesExt, WriteBytesExt};
use std::io::{Error, ErrorKind, Read, Result, Seek, SeekFrom, Write};
pub use super::Export;
fn fill_in_flags(export: &mut Export, flags: u16) {
if flags & NBD_FLAG_HAS_FLAGS != 0 {
if flags & NBD_FLAG_READ_ONLY != 0 {
export.readonly = true;
}
if flags & NBD_FLAG_SEND_RESIZE != 0 {
export.resizeable = true;
}
if flags & NBD_FLAG_ROTATIONAL != 0 {
export.rotational = true;
}
if flags & NBD_FLAG_SEND_TRIM != 0 {
export.send_trim = true;
}
if flags & NBD_FLAG_SEND_FLUSH != 0 {
export.send_flush = true;
}
}
}
/// Negotiate with a server, use before creating the actual client
pub fn handshake<IO: Write + Read>(mut c: IO, name: &[u8]) -> Result<Export> {
let mut signature = [0; 8];
c.read_exact(&mut signature)?;
if signature != *b"NBDMAGIC" {
strerror("Invalid magic1")?;
}
c.read_exact(&mut signature)?;
let (size, flags) = if signature == *b"IHAVEOPT" {
// newstyle
let _hs_flags = c.read_u16::<BE>()?;
c.write_u32::<BE>(NBD_FLAG_C_FIXED_NEWSTYLE)?;
// optmagic
c.write_u64::<BE>(0x49484156454F5054)?;
c.write_u32::<BE>(NBD_OPT_EXPORT_NAME)?;
c.write_u32::<BE>(name.len() as u32)?;
c.write_all(name)?;
c.flush()?;
let size = c.read_u64::<BE>()?;
let flags = c.read_u16::<BE>()?;
let mut z = [0; 124];
c.read_exact(&mut z)?;
if z[..] != [0; 124][..] {
strerror("Expected 124 bytes of zeroes are not zeroes")?;
}
(size, flags)
} else if signature == *b"\x00\x00\x42\x02\x81\x86\x12\x53" {
// oldstyle.
// Note: not tested at all
if name != b"" {
strerror("Old style server does not support named exports")?;
};
let size = c.read_u64::<BE>()?;
let flags = c.read_u32::<BE>()?;
let mut z = [0; 124];
c.read_exact(&mut z)?;
if z[..] != [0; 124][..] {
strerror("Expected 124 bytes of zeroes are not zeroes")?;
}
// Is it those flags or some other flags?
// Too lazy to actually look into NBD implementation.
let flags = flags as u16;
(size, flags)
} else {
strerror("Invalid magic2")?;
unreachable!()
};
let mut e = Export::default();
e.size = size;
fill_in_flags(&mut e, flags);
Ok(e)
}
/// Represents NBD client. Use `Read`,`Write` and `Seek` trait methods,
/// but make sure those are block-aligned
pub struct NbdClient<IO: Write + Read> {
c: IO,
seek_pos: u64,
size: u64,
}
impl<IO: Write + Read> NbdClient<IO> {
/// Create new NbdClient from `Export` returned from `handshake`.
/// Obviously, the `c` connection should be the same as in `handshake`.
pub fn new(c: IO, export: &Export) -> Self {
NbdClient {
c,
seek_pos: 0,
size: export.size,
}
}
}
impl<IO: Write + Read> Seek for NbdClient<IO> {
fn seek(&mut self, sf: SeekFrom) -> Result<u64> {
match sf {
SeekFrom::Start(x) => {
self.seek_pos = x;
}
SeekFrom::Current(x) => {
if let Some(xx) = self.seek_pos.checked_add_i64(x) {
self.seek_pos = xx;
} else {
strerror("Invalid seek")?;
}
}
SeekFrom::End(x) => {
if let Some(xx) = self.size.checked_add_i64(x) {
self.seek_pos = xx;
} else {
strerror("Invalid seek")?;
}
}
}
Ok(self.seek_pos)
}
}
fn check_err(error: u32) -> Result<()> {
match error {
1 => Err(Error::new(ErrorKind::PermissionDenied, "from device")),
5 => Err(Error::new(ErrorKind::Other, "EIO")),
12 => Err(Error::new(ErrorKind::Other, "ENOMEM")),
22 => Err(Error::new(ErrorKind::Other, "EINVAL")),
28 => Err(Error::new(ErrorKind::Other, "ENOSPC")),
0 => Ok(()),
_ => Err(Error::new(ErrorKind::Other, "other error from device")),
}
}
fn getreply<IO: Write + Read>(mut c: IO) -> Result<()> {
let signature = c.read_u32::<BE>()?;
let error = c.read_u32::<BE>()?;
let handle = c.read_u64::<BE>()?;
if signature != 0x67446698 {
strerror("Invalid signature for incoming reply")?;
}
if handle != 0 {
strerror("Unexpected handle")?;
};
check_err(error)?;
Ok(())
}
fn sendrequest<IO: Write + Read>(mut c: IO, cmd: u16, offset: u64, len: u32) -> Result<()> {
c.write_u32::<BE>(0x25609513)?;
c.write_u16::<BE>(0)?; // flags
c.write_u16::<BE>(cmd)?;
c.write_u64::<BE>(0)?; // handle
c.write_u64::<BE>(offset)?;
c.write_u32::<BE>(len)?;
c.flush()?;
Ok(())
}
impl<IO: Write + Read> NbdClient<IO> {
fn get_effective_len(&self, buflen: usize) -> Result<u32> {
if self.seek_pos == self.size {
return Ok(0);
}
if self.seek_pos > self.size {
strerror("Trying to read or write past the end of the device")?;
}
let maxlen = (self.size - self.seek_pos).clamp_to_u32();
let len = buflen.clamp_to_u32().min(maxlen);
Ok(len)
}
}
impl<IO: Write + Read> Read for NbdClient<IO> {
fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
let len = self.get_effective_len(buf.len())?;
if len == 0 {
return Ok(0);
}
sendrequest(&mut self.c, NBD_CMD_READ, self.seek_pos, len)?;
getreply(&mut self.c)?;
self.c.read_exact(&mut buf[0..(len as usize)])?;
self.seek_pos += len as u64;
Ok(len as usize)
}
}
impl<IO: Write + Read> Write for NbdClient<IO> {
fn write(&mut self, buf: &[u8]) -> Result<usize> {
let len = self.get_effective_len(buf.len())?;
if len == 0 {
return Ok(0);
}
sendrequest(&mut self.c, NBD_CMD_WRITE, self.seek_pos, len)?;
self.c.write_all(&buf[0..(len as usize)])?;
self.c.flush()?;
getreply(&mut self.c)?;
self.seek_pos += len as u64;
Ok(len as usize)
}
fn flush(&mut self) -> Result<()> {
sendrequest(&mut self.c, NBD_CMD_FLUSH, 0, 0)?;
getreply(&mut self.c)?;
Ok(())
}
}
/// Additional operations (apart from reading and writing) supported by NBD extensions
/// Not tested yet.
pub trait NbdExt {
/// Discard this data, starting from current seek offset up to specified length
fn trim(&mut self, length: usize) -> Result<()>;
/// Change size of the device
fn resize(&mut self, newsize: u64) -> Result<()>;
}
impl<IO: Write + Read> NbdExt for NbdClient<IO> {
fn trim(&mut self, length: usize) -> Result<()> {
let len = self.get_effective_len(length)?;
if len == 0 {
return Ok(());
}
sendrequest(&mut self.c, NBD_CMD_TRIM, self.seek_pos, len)?;
getreply(&mut self.c)?;
Ok(())
}
fn resize(&mut self, newsize: u64) -> Result<()> {
sendrequest(&mut self.c, NBD_CMD_RESIZE, newsize, 0)?;
getreply(&mut self.c)?;
self.size = newsize;
Ok(())
}
}
}
#[allow(dead_code)]
mod consts {
pub const NBD_OPT_EXPORT_NAME: u32 = 1;
pub const NBD_OPT_ABORT: u32 = 2;
pub const NBD_OPT_LIST: u32 = 3;
pub const NBD_OPT_STARTTLS: u32 = 5;
pub const NBD_OPT_INFO: u32 = 6;
pub const NBD_OPT_GO: u32 = 7;
pub const NBD_OPT_STRUCTURED_REPLY: u32 = 8;
pub const NBD_OPT_EXTENDED_HEADERS: u32 = 11;
pub const NBD_REP_ACK: u32 = 1;
pub const NBD_REP_SERVER: u32 = 2;
pub const NBD_REP_INFO: u32 = 3;
pub const NBD_REP_FLAG_ERROR: u32 = 1 << 31;
pub const NBD_REP_ERR_UNSUP: u32 = 1 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_POLICY: u32 = 2 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_INVALID: u32 = 3 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_PLATFORM: u32 = 4 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_TLS_REQD: u32 = 5 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_UNKNOWN: u32 = 6 | NBD_REP_FLAG_ERROR;
pub const NBD_REP_ERR_BLOCK_SIZE_REQD: u32 = 8 | NBD_REP_FLAG_ERROR;
pub const NBD_FLAG_FIXED_NEWSTYLE: u16 = 1 << 0;
pub const NBD_FLAG_NO_ZEROES: u16 = 1 << 1;
pub const NBD_FLAG_C_FIXED_NEWSTYLE: u32 = NBD_FLAG_FIXED_NEWSTYLE as u32;
pub const NBD_FLAG_C_NO_ZEROES: u32 = NBD_FLAG_NO_ZEROES as u32;
pub const NBD_INFO_EXPORT: u16 = 0;
pub const NBD_INFO_NAME: u16 = 1;
pub const NBD_INFO_DESCRIPTION: u16 = 2;
pub const NBD_INFO_BLOCK_SIZE: u16 = 3;
pub const NBD_FLAG_HAS_FLAGS: u16 = 1 << 0;
pub const NBD_FLAG_READ_ONLY: u16 = 1 << 1;
pub const NBD_FLAG_SEND_FLUSH: u16 = 1 << 2;
pub const NBD_FLAG_SEND_FUA: u16 = 1 << 3;
pub const NBD_FLAG_ROTATIONAL: u16 = 1 << 4;
pub const NBD_FLAG_SEND_TRIM: u16 = 1 << 5;
pub const NBD_FLAG_SEND_WRITE_ZEROES: u16 = 1 << 6;
pub const NBD_FLAG_CAN_MULTI_CONN: u16 = 1 << 8;
pub const NBD_FLAG_SEND_RESIZE: u16 = 1 << 9;
pub const NBD_CMD_READ: u16 = 0;
pub const NBD_CMD_WRITE: u16 = 1;
pub const NBD_CMD_DISC: u16 = 2;
pub const NBD_CMD_FLUSH: u16 = 3;
pub const NBD_CMD_TRIM: u16 = 4;
pub const NBD_CMD_WRITE_ZEROES: u16 = 6;
pub const NBD_CMD_RESIZE: u16 = 8;
}
trait CheckedAddI64
where
Self: Sized,
{
fn checked_add_i64(self, rhs: i64) -> Option<Self>;
}
impl CheckedAddI64 for u64 {
fn checked_add_i64(self, rhs: i64) -> Option<Self> {
if rhs >= 0 {
self.checked_add(rhs as u64)
} else {
if let Some(x) = rhs.checked_neg() {
self.checked_sub(x as u64)
} else {
None
}
}
}
}
trait ClampToU32
where
Self: Sized,
{
fn clamp_to_u32(self) -> u32;
}
impl ClampToU32 for usize {
fn clamp_to_u32(self) -> u32 {
if self > u32::max_value() as usize {
u32::max_value()
} else {
self as u32
}
}
}
impl ClampToU32 for u64 {
fn clamp_to_u32(self) -> u32 {
if self > u32::max_value() as u64 {
u32::max_value()
} else {
self as u32
}
}
}
/*
// Options that the client can select to the server
#define NBD_OPT_EXPORT_NAME (1) // Client wants to select a named export (is followed by name of export)
#define NBD_OPT_ABORT (2) // Client wishes to abort negotiation
#define NBD_OPT_LIST (3) // Client request list of supported exports (not followed by data)
#define NBD_OPT_STARTTLS (5) // Client wishes to initiate TLS
#define NBD_OPT_INFO (6) // Client wants information about the given export
#define NBD_OPT_GO (7) // Client wants to select the given and move to the transmission phase
// Replies the server can send during negotiation
#define NBD_REP_ACK (1) // ACK a request. Data: option number to be acked
#define NBD_REP_SERVER (2) // Reply to NBD_OPT_LIST (one of these per server; must be followed by NBD_REP_ACK to signal the end of the list
#define NBD_REP_INFO (3) // Reply to NBD_OPT_INFO
#define NBD_REP_FLAG_ERROR (1 << 31) // If the high bit is set, the reply is an error
#define NBD_REP_ERR_UNSUP (1 | NBD_REP_FLAG_ERROR) // Client requested an option not understood by this version of the server
#define NBD_REP_ERR_POLICY (2 | NBD_REP_FLAG_ERROR) // Client requested an option not allowed by server configuration. (e.g., the option was disabled)
#define NBD_REP_ERR_INVALID (3 | NBD_REP_FLAG_ERROR) // Client issued an invalid request
#define NBD_REP_ERR_PLATFORM (4 | NBD_REP_FLAG_ERROR) // Option not supported on this platform
#define NBD_REP_ERR_TLS_REQD (5 | NBD_REP_FLAG_ERROR) // TLS required
#define NBD_REP_ERR_UNKNOWN (6 | NBD_REP_FLAG_ERROR) // NBD_OPT_INFO or ..._GO requested on unknown export
#define NBD_REP_ERR_BLOCK_SIZE_REQD (8 | NBD_REP_FLAG_ERROR) // Server is not willing to serve the export without the block size being negotiated
// Global flags
#define NBD_FLAG_FIXED_NEWSTYLE (1 << 0) // new-style export that actually supports extending
#define NBD_FLAG_NO_ZEROES (1 << 1) // we won't send the 128 bits of zeroes if the client sends NBD_FLAG_C_NO_ZEROES
// Flags from client to server.
#define NBD_FLAG_C_FIXED_NEWSTYLE NBD_FLAG_FIXED_NEWSTYLE
#define NBD_FLAG_C_NO_ZEROES NBD_FLAG_NO_ZEROES
// Info types
#define NBD_INFO_EXPORT (0)
#define NBD_INFO_NAME (1)
#define NBD_INFO_DESCRIPTION (2)
#define NBD_INFO_BLOCK_SIZE (3)
// values for flags field
#define NBD_FLAG_HAS_FLAGS (1 << 0) // Flags are there
#define NBD_FLAG_READ_ONLY (1 << 1) // Device is read-only
#define NBD_FLAG_SEND_FLUSH (1 << 2) // Send FLUSH
#define NBD_FLAG_SEND_FUA (1 << 3) // Send FUA (Force Unit Access)
#define NBD_FLAG_ROTATIONAL (1 << 4) // Use elevator algorithm - rotational media
#define NBD_FLAG_SEND_TRIM (1 << 5) // Send TRIM (discard)
#define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) // Send NBD_CMD_WRITE_ZEROES
#define NBD_FLAG_CAN_MULTI_CONN (1 << 8) // multiple connections are okay
*/