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// vim: tw=80 // Copyright (C) 2020 Axcient // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // // * Redistributions in binary form must reproduce the above copyright // notice, this list of conditions and the following disclaimer in the // documentation and/or other materials provided with the distribution. // // THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, // THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A // PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR // CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF // USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND // ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT // OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF // SUCH DAMAGE. //! Rust bindings to NBDKit. //! //! NBDKit is a toolkit for building Network Block Device servers. //! //! [https://github.com/libguestfs/nbdkit](https://github.com/libguestfs/nbdkit) //! //! To use nbdkit, build your project as a cdylib. Define your plugin by //! implementing [`Server`], and then register it with [`plugin!`]. See //! ramdisk.rs in the source code for a complete example. //! //! ```no_run //! # use nbdkit::*; //! #[derive(Default)] //! struct MyPlugin { //! // ... //! # _not_used: i32, //! } //! impl Server for MyPlugin { //! fn get_size(&self) -> Result<i64> { //! // ... //! # Ok(0) //! } //! //! fn name() -> &'static str { //! "my_plugin" //! } //! //! fn open(_readonly: bool) -> Box<dyn Server> { //! Box::new(MyPlugin::default()) //! } //! //! fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<()> { //! // ... //! # Ok(()) //! } //! } //! plugin!(MyPlugin {}); //! # fn main() {} //! ``` #![cfg_attr(feature = "nightly-docs", feature(doc_cfg))] #![deny(missing_docs)] use bitflags::bitflags; #[cfg(feature = "nix")] #[cfg_attr(feature = "nightly-docs", doc(cfg(feature = "nix")))] pub use nix::sys::socket::{SockAddr, sockaddr_storage_to_addr}; use std::{ ffi::{CStr, CString}, error, fmt, io, mem, os::raw::{c_char, c_int, c_void}, ptr, slice, sync::Once, }; /// The error type used by [`Result`]. #[derive(Debug)] pub struct Error { source: Box<dyn error::Error + 'static>, errno: i32 } impl Error { fn errno(&self) -> i32 { self.errno } /// Create a new Error with a supplied errno. /// /// # Examples /// ``` /// # use nbdkit::Error; /// let e = Error::new(libc::EINVAL, "Invalid value for option foo"); /// ``` pub fn new<E>(errno: i32, error: E) -> Error where E: Into<Box<dyn error::Error + 'static>> { Error { source: error.into(), errno } } } impl error::Error for Error { fn source(&self) -> Option<&(dyn error::Error + 'static)> { Some(&*self.source) } } impl fmt::Display for Error { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.source.fmt(f) } } impl From<io::Error> for Error { fn from(e: io::Error) -> Error { Error { errno: e.raw_os_error().unwrap_or(0), source: Box::new(e), } } } /// The Result type returned by all [`Server`] callbacks. pub type Result<T> = std::result::Result<T, Error>; static mut INITIALIZED: bool = false; mod unreachable { use super::*; pub(super) fn config(_k: &str, _v: &str) -> Result<()> { unreachable!() } pub(super) fn config_complete() -> Result<()> { unreachable!() } pub(super) fn dump_plugin() { unreachable!() } pub(super) fn open(_: bool) -> Box<dyn Server> { unreachable!() } pub(super) fn preconnect(_: bool) -> Result<()> { unreachable!() } pub(super) fn thread_model() -> Result<ThreadModel> { unreachable!() } } static mut CONFIG: fn(k: &str, v: &str) -> Result<()> = unreachable::config; static mut CONFIG_COMPLETE: fn() -> Result<()> = unreachable::config_complete; static mut CONFIG_HELP: Vec<u8> = Vec::new(); static mut DESCRIPTION: Vec<u8> = Vec::new(); static mut DUMP_PLUGIN: fn() = unreachable::dump_plugin; static mut GET_READY: fn() -> Result<()> = unreachable::config_complete; static mut LOAD: fn() = unreachable::dump_plugin; static mut LONGNAME: Vec<u8> = Vec::new(); static mut MAGIC_CONFIG_KEY: Vec<u8> = Vec::new(); static mut NAME: Vec<u8> = Vec::new(); static mut OPEN: fn(readonly: bool) -> Box<dyn Server> = unreachable::open; static mut PRECONNECT: fn(readonly: bool) -> Result<()> = unreachable::preconnect; static mut THREAD_MODEL: fn() -> Result<ThreadModel> = unreachable::thread_model; static mut UNLOAD: fn() = unreachable::dump_plugin; static mut VERSION: Vec<u8> = Vec::new(); static INIT: Once = Once::new(); bitflags! { /// Flags used by multiple [`Server`] methods pub struct Flags: u32 { /// This flag is used by the [`Server::zero`] callback. /// /// Indicates that the plugin may punch a hole instead of writing actual /// zeros, but only if subsequent reads from that region will return /// zeros. There is no way to disable this flag, although a plugin that /// does not support trim as a way to write zeroes may ignore the flag /// without violating expected semantics. const MAY_TRIM = 0b00000001; /// This flag represents Forced Unit Access semantics. /// /// It is used by the [`Server::write_at`], [`Server::zero`], and /// [`Server::trim`] callbacks to indicate that the plugin must not /// return a result until the action has landed in persistent storage. /// This flag will not be sent to the plugin unless `can_fua` is /// provided to [`plugin!`] and [`Server::can_fua`] returns /// [`FuaFlags::Native`]. const FUA = 0b00000010; /// Used with [`Server::extents`] to indicate that the client is only /// requesting information about a single extent. The plugin may ignore /// this flag, or as an optimization it may return /// just a single extent. const REQ_ONE = 0b00000100; /// This flag is used by [`Server::zero`]. /// /// If supplied, the plugin must decide up front if the implementation /// is likely to be faster than a corresponding [`Server::write_at`]; if /// not, then it must immediately fail with `ENOTSUP` or /// `EOPNOTSUPP` and preferably without modifying the exported /// image. It is acceptable to always fail a fast zero request (as a /// fast failure is better than attempting the write only to find out /// after the fact that it was not fast after all). Note that on Linux, /// support for `ioctl(BLKZEROOUT)` is insufficient for determining /// whether a zero request to a block device will be fast (because the /// kernel will perform a slow fallback when needed). const FAST_ZERO = 0b00001000; } } /// Return values for [`Server::can_cache`] #[repr(i32)] pub enum CacheFlags { /// Cache support is not advertised to the client. None = 0, /// Caching is emulated by the server calling [`Server::read_at`] and /// ignoring the results. Emulate = 1, /// The [`Server::cache`] callback will be used. Native = 2, } impl Into<i32> for CacheFlags { fn into(self) -> i32 { self as i32 } } /// Return values for [`Server::can_fua`] #[repr(i32)] pub enum FuaFlags { /// FUA support is not advertised to the client None = 0, /// The [`Server::flush`] callback must work (even if [`Server::can_flush`] /// returns false), and FUA support is emulated by calling `Server::flush` /// after any write operation; Emulate = 1, /// The [`Server::write_at`], [`Server::zero`], and [`Server::trim`] /// callbacks (if implemented) must handle the flag [`Flags::FUA`], by not /// returning until that action has landed in persistent storage. Native = 2, } impl Into<i32> for FuaFlags { fn into(self) -> i32 { self as i32 } } /// A plugin's maximum thread safety model #[derive(Clone, Copy, Debug, Eq, PartialEq)] #[repr(i32)] pub enum ThreadModel { /// Only a single handle can be open at any time, and all requests happen /// from one thread. SerializeConnections = 0, /// Multiple handles can be open at the same time, but requests are /// serialized so that for the plugin as a whole only one /// open/read/write/close (etc) request will be in progress at any time. /// /// This is a useful setting if the library you are using is not /// thread-safe. However performance may not be good. SerializeAllRequests = 1, /// Multiple handles can be open and multiple data requests can happen in /// parallel. However only one request will happen per handle at a time (but /// requests on different handles might happen concurrently). SerializeRequests = 2, /// Multiple handles can be open and multiple data requests can happen in /// parallel (even on the same handle). The server may reorder replies, /// answering a later request before an earlier one. /// /// All the libraries you use must be thread-safe and reentrant, and any /// code that creates a file descriptor should atomically set `FD_CLOEXEC` /// if you do not want it accidentally leaked to another thread's child /// process. You may also need to provide mutexes for fields in your /// connection handle. Parallel = 3, } /// Used by [`Server::extents`] to report extents to the client #[derive(Clone, Copy, Debug, Eq, PartialEq)] #[repr(u32)] pub enum ExtentType { /// A normal, allocated data extent Allocated = 0, /// An unallocated extent (hole) which does not read back as zeroes. Note /// this should only be used in specialized circumstances such as when /// writing a plugin for (or to emulate) certain SCSI drives which do not /// guarantee that trimmed blocks read back as zeroes. Hole = 1, /// An allocated extent which is known to contain only zeroes. Zero = 2, /// An unallocated extent, a.k.a. a “hole”, which reads back as zeroes. This /// is the normal type of hole applicable to most disks. HoleZero = 3 } /// Used by [`Server::extents`] to report extents to the client #[derive(Debug)] pub struct ExtentHandle(*mut c_void); impl ExtentHandle { /// Report a single extent spanning `[offset .. offset + len)` back to the /// client. pub fn add(&mut self, offset: u64, len: u64, et: ExtentType) -> Result<()> { let r = unsafe { nbdkit_add_extent(self.0, offset, len, et as u32) }; match r { 0 => Ok(()), -1 => Err(io::Error::last_os_error().into()), x => panic!("Undocumented return value {} from nbdkit_add_extent", x) } } } /// All the FFI functions called by C code mod ffi { use super::*; macro_rules! can_method { ( $meth:ident ) => { pub(super) extern fn $meth(h: *mut c_void) -> c_int { let server = unsafe { downcast(h) }; match server.$meth() { Err(e) => { set_error(e); -1 }, Ok(x) => x.into(), } } } } macro_rules! trim_like { ( $meth:ident) => { pub(super) extern fn $meth(h: *mut c_void, count: u32, offset: u64, rawflags: u32) -> c_int { let server = unsafe { downcast(h) }; let flags = Flags::from_bits(rawflags) .expect(&format!("Unknown flags value {:#x?}", rawflags)); match server.$meth(count, offset, flags) { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } } } pub(super) extern fn cache(h: *mut c_void, count: u32, offset: u64, _rawflags: u32) -> c_int { let server = unsafe { downcast(h) }; match server.cache(count, offset) { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn close(selfp: *mut c_void) { unsafe { Box::from_raw(selfp as *mut Box<dyn Server>); } } can_method!(can_cache); can_method!(can_extents); can_method!(can_flush); can_method!(can_fua); can_method!(can_fast_zero); can_method!(can_multi_conn); can_method!(can_write); can_method!(can_trim); can_method!(can_zero); pub(super) extern fn config(k: *const c_char, v: *const c_char) -> c_int { let key = match unsafe { CStr::from_ptr(k) }.to_str() { Ok(s) => s, Err(e) => { let error = Error::new(libc::EINVAL, e.to_string()); set_error(error); return -1; } }; let value = match unsafe { CStr::from_ptr(v) }.to_str() { Ok(s) => s, Err(e) => { let error = Error::new(libc::EINVAL, e.to_string()); set_error(error); return -1; } }; match unsafe { CONFIG(key, value) } { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn config_complete() -> c_int { match unsafe { CONFIG_COMPLETE() } { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } /// Deference the pointer into a trait object reference /// /// # Safety /// /// The pointer must be a valid pointer to `Box<Box<dyn Server>>`. The /// pointer's lifetime must be valid for the duration of the returned /// reference. unsafe fn downcast<'a>(p: *const c_void) -> &'a dyn Server { &**(p as *const Box<dyn Server>) } pub(super) extern fn dump_plugin() { unsafe { DUMP_PLUGIN() } } // TODO: document REQ_ONE pub(super) extern fn extents(h: *mut c_void, count: u32, offset: u64, rawflags: u32, extents: *mut c_void ) -> c_int { let server = unsafe { downcast(h) }; let mut exh = ExtentHandle(extents); let flags = Flags::from_bits(rawflags).expect("Unknown extents flags"); match server.extents(count, offset, flags, &mut exh) { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn flush(h: *mut c_void, _rawflags: u32) -> c_int { let server = unsafe { downcast(h) }; match server.flush() { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn get_ready() -> c_int { match unsafe { GET_READY() } { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn get_size(h: *mut c_void) -> i64 { let server = unsafe { downcast(h) }; match server.get_size() { Ok(size) => size, Err(e) => { set_error(e); -1 } } } can_method!(is_rotational); pub(super) extern fn load() { unsafe { LOAD() } } pub(super) extern fn open(readonly: c_int) -> *mut c_void { // We need to double-box to turn the trait object (fat pointer) into a // thin pointer let server = Box::new(unsafe{OPEN(readonly != 0)}); // Leak the memory to C. We'll get it back in close Box::into_raw(server) as *mut c_void } pub(super) extern fn pread(h: *mut c_void, bufp: *mut c_char, count: u32, offset: u64, _flags: u32) -> c_int { let server = unsafe { downcast(h) }; let buf = unsafe { slice::from_raw_parts_mut(bufp as *mut u8, count as usize) }; match server.read_at(buf, offset) { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn preconnect(readonly: c_int) -> c_int { match unsafe { PRECONNECT(readonly != 0) } { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } pub(super) extern fn pwrite(h: *mut c_void, bufp: *const c_char, count: u32, offset: u64, rawflags: u32) -> c_int { let server = unsafe { downcast(h) }; let buf = unsafe { slice::from_raw_parts(bufp as *mut u8, count as usize) }; let flags = Flags::from_bits(rawflags).expect("Unknown pwrite flags"); match server.write_at(buf, offset, flags) { Ok(()) => 0, Err(e) => { set_error(e); -1 } } } fn set_error(e: Error) { let fmt = CString::new("%s").unwrap(); let msg = CString::new(e.to_string()).expect("CString::new"); unsafe { nbdkit_error(fmt.as_ptr(), msg.as_ptr()); nbdkit_set_error(e.errno()); } } pub(super) extern fn thread_model() -> c_int { match unsafe { THREAD_MODEL() } { Ok(x) => x as c_int, Err(e) => { set_error(e); -1 } } } trim_like!(trim); pub(super) extern fn unload() { unsafe { UNLOAD() } } trim_like!(zero); } /// Define the entry point for your plugin. /// /// Any of the optional methods may be implemented. If so, each must be /// registered with [`plugin!`]. It is an error to register any method that you /// don't implement. // We want the argument names to show up without underscores in the API docs #[allow(unused_variables)] pub trait Server { /// Indicates that the client intends to make further accesses to the given /// data region. /// /// The nature of caching is not specified further by the NBD specification /// (for example, a server may place limits on how much may be cached at /// once, and there is no way to control if writes to a cached area have /// write-through or write-back semantics). In fact, the cache command can /// always fail and still be compliant, and success might not guarantee a /// performance gain. If this callback is omitted, then the results of /// [`Server::can_cache`] determine whether nbdkit will reject cache /// requests, treat them as instant success, or emulate caching by calling /// [`Server::pread` over the same region and ignoring the results. fn cache(&self, count: u32, offset: u64) -> Result<()> { unimplemented!() } /// Indicate level of cacheing support to the client. /// /// This is called during the option negotiation phase to find out if the /// plugin supports a cache operation. The nature of the caching is /// unspecified (including whether there are limits on how much can be /// cached at once, and whether writes to a cached region have write-through /// or write-back semantics), but the command exists to let clients issue a /// hint to the server that they will be accessing that region of the /// export. fn can_cache(&self) -> Result<CacheFlags> { unimplemented!() } /// Indicate to the client whether the plugin supports detecting allocated /// (non-sparse) regions of the disk with the [`Server::extents`] fn can_extents(&self) -> Result<bool> { unimplemented!() } /// Indicate to the client wheter the plugin supports the flush-to-disk /// operation. fn can_flush(&self) -> Result<bool> { unimplemented!() } /// Indicate to the client whether the plugin supports fast-zero requests. fn can_fast_zero(&self) -> Result<bool> { unimplemented!() } /// Indicate to the client whether the plugin supports Forced Unit Access /// (FUA) flag on write, trim, and zero requests. /// /// If this callback is not implemented, then nbdkit checks whether /// [`Server::flush`] is implemented, /// exists, and behaves as if this function returns [`FuaFlags::None`] or /// [`FuaFlags::Emulate`] as appropriate. fn can_fua(&self) -> Result<FuaFlags> { unimplemented!() } /// Indicate to the client whether the plugin is prepared to handle multiple /// connections from a single client. /// /// If thie method returns `true` then a /// client may try to open multiple connections to the nbdkit server and /// spread requests across all connections to maximize parallelism. If it /// returns `false` false (which is the default) then well-behaved clients /// should only open a single connection, although we cannot control what /// clients do in practice. /// /// Specifically it means that either the plugin does not cache requests at /// all, or if it does cache them then the effects of a [`Server::flush`] /// request or setting [`Flags::FUA`] on a write/trim/zero must be visible /// across all connections to the plugin before the plugin replies to that /// request. fn can_multi_conn(&self) -> Result<bool> { unimplemented!() } /// Indicate to the client whether the plugin supports the trim/discard /// operation for punching holes in the backing store. fn can_trim(&self) -> Result<bool> { unimplemented!() } /// Indicates to the client whether the plugin supports writes fn can_write(&self) -> Result<bool> { unimplemented!() } /// Indicates to the client whether the [`Server::zero`] callback should be /// used. /// /// Support for writing zeroes is still advertised to the client, so /// returning false merely serves as a way to avoid complicating the /// [`Server::zero`] callback to have to fail with `ENOTSUP` or /// `EOPNOTSUPP` on the connections where it will never be more efficient /// than using [`Server::write_at`] up front. fn can_zero(&self) -> Result<bool> { unimplemented!() } /// Supplies command-line parameters, one at a time, to the plugin. /// /// On the nbdkit command line, after the plugin filename, come an optional /// list of key=value arguments. These are passed to the plugin through this /// callback when the plugin is first loaded and before any connections are /// accepted. /// /// This callback may be called zero or more times. /// /// The key will be a non-empty string beginning with an ASCII alphabetic /// character (A-Z a-z). The rest of the key must contain only ASCII /// alphanumeric plus period, underscore or dash characters (A-Z a-z 0-9 . _ /// -). The value may be an arbitrary string, including an empty string. /// /// The names of keys accepted by plugins is up to the plugin, but you /// should probably look at other plugins and follow the same conventions. fn config(key: &str, value: &str) -> Result<()> where Self: Sized { unimplemented!() } /// This optional callback is called after all the configuration has been /// passed to the plugin. /// /// It is a good place to do checks, for example that the user has passed /// the required parameters to the plugin. fn config_complete() -> Result<()> where Self: Sized { unimplemented!() } /// This optional callback is called when the `nbdkit plugin --dump-plugin` /// command is used. It should print any additional informative key=value /// fields to stdout as needed. Prefixing the keys with the name of the /// plugin will avoid conflicts. fn dump_plugin() where Self: Sized { unimplemented!() } /// This optional multi-line help message should summarize any key=value /// parameters that it takes. It does not need to repeat what already /// appears in [`Server::description`]. fn config_help() -> Option<&'static str> where Self: Sized { None } /// An optional multi-line description of the plugin. fn description() -> Option<&'static str> where Self: Sized { None } /// During the data serving phase, this callback is used to detect /// allocated, sparse and zeroed regions of the disk. /// /// This function will not be called if [`Server::can_extents`] returned `false`. /// nbdkit's default behaviour in this case is to treat the whole virtual /// disk as if it were allocated. Also, this function will not be called by /// a client that does not request structured replies (the `--no-sr` option /// of nbdkit can be used to test behavior when `extents` is unavailable to /// the client). /// /// The callback should detect and return the list of extents overlapping /// the range `[offset...offset+count)`. Each extent should be reported /// by calling [`ExtentHandle::add`]. /// /// The flags parameter of the `extents` callback may contain /// [`Flags::REQ_ONE`]. This means that the client is only requesting /// information about the extent overlapping `offset`. The plugin may ignore /// this flag, or as an optimization it may return just a single extent for /// offset. // Alternatively, the method could be defined as returning a Vec of extent // objects, rather than using the ExtentHandle. I'm not sure which would be // more ergonomic, but this way requires fewer memory allocations. fn extents(&self, count: u32, offset: u64, flags: Flags, extent_handle: &mut ExtentHandle) -> Result<()> { unimplemented!() } /// During the data serving phase, this callback is used to sync the /// backing store, ie. to ensure it has been completely written to a /// permanent medium. If that is not possible then you can omit this /// callback. /// /// This function will not be called directly by the client if /// [`Server::can_flush`] returned `false`; however, it may still be called /// by nbdkit if [`Server::can_fua`] returned [`FuaFlags::Emulate`]. fn flush(&self) -> Result<()> { unimplemented!() } /// This optional callback is called before the server starts serving. /// /// It is called before the server forks or changes directory. It is the /// last chance to do any global preparation that is needed to serve /// connections. fn get_ready() -> Result<()> where Self: Sized { unimplemented!() } /// Return the size in bytes of the exported block device fn get_size(&self) -> Result<i64>; /// Return `true` if the backing store is a rotational medium (like a /// traditional hard disk) as opposed to a non-rotating one like an SSD. /// /// This may cause the client to reorder requests to make them more /// efficient for a slow rotating disk. fn is_rotational(&self) -> Result<bool> { unimplemented!() } /// This is called once just after the plugin is loaded into memory. You can /// use this to perform any global initialization needed by the plugin. fn load() where Self: Sized { unimplemented!() } /// An optional free text name of the plugin. This field is used in error /// messages. fn longname() -> Option<&'static str> where Self: Sized { None } /// This optional string can be used to set a "magic" key used when parsing /// plugin parameters. It affects how "bare parameters" (those which do not /// contain an = character) are parsed on the command line. /// /// If `magic_config_key().is_some()` then any bare parameters are passed to /// the [`Server::config`] method as: `config (magic_config_key, argv[i]);`. /// /// If `magic_config_key().is_none()` then we behave as in nbdkit < 1.7: If /// the first parameter on the command line is bare then it is passed to the /// `Server::config` method as: `config("script", value);`. Any other bare /// parameters give errors. fn magic_config_key() -> Option<&'static str> where Self: Sized { None } /// The name of the plugin. /// /// It must contain only ASCII alphanumeric characters and be unique amongst /// all plugins. fn name() -> &'static str where Self: Sized; /// Allocate and return a new `Server` handle to the client. /// /// Called whenever a new client connects to the server. The `readonly` /// flag informs the plugin that the server was started with the -r flag on /// the command line which forces connections to be read-only. Note that the /// plugin may *additionally* force the connection to be readonly (even if /// this flag is false) by returning false from the [`Server::can_write`] /// callback. So if your plugin can only serve read-only, you can ignore /// this parameter. fn open(readonly: bool) -> Box<dyn Server> where Self: Sized; /// This optional callback is called when a TCP connection has been made to /// the server. This happens early, before NBD or TLS negotiation. If TLS /// authentication is required to access the server, then it has not been /// negotiated at this point. /// /// For security reasons (to avoid denial of service attacks) this callback /// should be written to be as fast and take as few resources as possible. /// If you use this callback, only use it to do basic access control, such /// as checking [`peername`] against a whitelist. It may be better to do /// access control outside the server, for example using TCP wrappers or a /// firewall. /// /// The `readonly` flag informs the plugin that the server was started with /// the `-r` flag on the command line. /// /// Returning `Ok(())` will allow the connection to continue. If there is an /// error or you want to deny the connection, return an error. fn preconnect(readonly: bool) -> Result<()> where Self: Sized { unimplemented!() } /// Read data from the backing store, starting at `offset`. /// /// The callback must read the entire range if it can. If it, it should /// return an error. fn read_at(&self, buf: &mut [u8], offset: u64) -> Result<()>; /// This optional callback is called after all the configuration has been /// passed to the plugin. /// /// It can be used to force a stricter thread model than the default /// ([`ThreadModel::Parallel`]). fn thread_model() -> Result<ThreadModel> where Self: Sized { unimplemented!() } /// Punch a hole in the backing store. /// /// This function will not be called if [`Server::can_trim`] returned /// `false`. The parameter flags may include `Flags::FUA` on input based on /// the result of [`Server::can_fua`]. fn trim(&self, count: u32, offset: u64, flags: Flags) -> Result<()> { unimplemented!() } /// This may be called once just before the plugin is unloaded from memory. fn unload() where Self: Sized { unimplemented!() } /// An optional version string which is displayed in help and debugging /// output. fn version() -> Option<&'static str> where Self: Sized { None } /// Write data to the backing store. /// /// The `flags` argument may include [`Flags::FUA`] based on the result of /// [`Server::can_fua`]. /// /// The callback must write the entire range if it can. If it, it should /// return an error. fn write_at(&self, buf: &[u8], offset: u64, flags: Flags) -> Result<()> { unimplemented!() } /// Write consecutive zeros to the backing store. /// /// The callback must write the whole region if it can. The NBD protocol /// doesn't allow partial writes (instead, these are errors). /// /// If this callback is omitted, or if it fails with `ENOTSUP` or /// `EOPNOTSUPP` , then [`Server::write_at`] will be used as an /// automatic fallback except when the client requested a fast zero. /// /// # Arguments /// /// * `count`: Length of the region to write in bytes /// * `offset`: Offset of the region to write in the backing store. /// * `flags`: May include [`Flags::MAY_TRIM`], [`Flags::FAST_ZERO`], /// and/or [`Flags::FUA`]. fn zero(&self, count: u32, offset: u64, flags: Flags) -> Result<()> { unimplemented!() } } macro_rules! opt_method { ( $self:ident, $method:ident ) => { if $self.$method {Some(ffi::$method)} else {None} }; ( $self:ident, $method:ident, $ffi_method:ident ) => { if $self.$method {Some(ffi::$ffi_method)} else {None} } } /// Used by (`plugin!`)[macro.plugin.html], but should never be accessed /// directly by the user. #[doc(hidden)] #[derive(Default)] pub struct Builder { pub cache: bool, pub can_cache: bool, pub can_extents: bool, pub can_flush: bool, pub can_fast_zero: bool, pub can_fua: bool, pub can_multi_conn: bool, pub can_trim: bool, pub can_write: bool, pub can_zero: bool, pub config: bool, pub config_complete: bool, pub config_help: bool, pub dump_plugin: bool, pub extents: bool, pub flush: bool, pub get_ready: bool, pub is_rotational: bool, pub load: bool, pub preconnect: bool, pub thread_model: bool, pub trim: bool, pub unload: bool, pub write_at: bool, pub zero: bool, } impl Builder { #[doc(hidden)] pub fn into_ptr<S: Server>(self) -> *const Plugin { INIT.call_once(|| { unsafe { assert!(!INITIALIZED); INITIALIZED = true; CONFIG = S::config; CONFIG_COMPLETE = S::config_complete; DUMP_PLUGIN = S::dump_plugin; GET_READY = S::get_ready; LOAD = S::load; OPEN = S::open; PRECONNECT = S::preconnect; THREAD_MODEL = S::thread_model; UNLOAD = S::unload; NAME = CString::new(S::name()).unwrap().into_bytes_with_nul(); if let Some(s) = S::config_help() { CONFIG_HELP = CString::new(s).unwrap().into_bytes_with_nul(); } if let Some(s) = S::description() { DESCRIPTION = CString::new(s).unwrap().into_bytes_with_nul(); } if let Some(s) = S::longname() { LONGNAME = CString::new(s).unwrap().into_bytes_with_nul(); } if let Some(s) = S::magic_config_key() { MAGIC_CONFIG_KEY = CString::new(s).unwrap() .into_bytes_with_nul(); } if let Some(s) = S::version() { VERSION = CString::new(s).unwrap().into_bytes_with_nul(); } }; }); let config_help = S::config_help() .map(|_| unsafe {CONFIG_HELP.as_ptr()} as *const i8) .unwrap_or(ptr::null()); let description = S::description() .map(|_| unsafe {DESCRIPTION.as_ptr()} as *const i8) .unwrap_or(ptr::null()); let longname = S::longname() .map(|_| unsafe {LONGNAME.as_ptr()} as *const i8) .unwrap_or(ptr::null()); let magic_config_key = S::magic_config_key() .map(|_| unsafe {MAGIC_CONFIG_KEY.as_ptr()} as *const i8) .unwrap_or(ptr::null()); let version = S::version() .map(|_| unsafe {VERSION.as_ptr()} as *const i8) .unwrap_or(ptr::null()); let plugin = Plugin { _struct_size: mem::size_of::<Plugin>() as u64, _api_version: 2, _thread_model: ThreadModel::Parallel as c_int, name: unsafe{ NAME.as_ptr() } as *const i8, longname, version, description, load: opt_method!(self, load), unload: opt_method!(self, unload), config: opt_method!(self, config), config_complete: opt_method!(self, config_complete), config_help, open: ffi::open, close: ffi::close, get_size: ffi::get_size, can_write: opt_method!(self, can_write), can_flush: opt_method!(self, can_flush), is_rotational: opt_method!(self, is_rotational), can_trim: opt_method!(self, can_trim), _pread_v1: None, _pwrite_v1: None, _flush_v1: None, _trim_v1: None, _zero_v1: None, errno_is_preserved: 0, dump_plugin: opt_method!(self, dump_plugin), can_zero: opt_method!(self, can_zero), can_fua: opt_method!(self, can_fua), pread: ffi::pread, pwrite: opt_method!(self, write_at, pwrite), flush: opt_method!(self, flush), trim: opt_method!(self, trim), zero: opt_method!(self, zero), magic_config_key, can_multi_conn: opt_method!(self, can_multi_conn), can_extents: opt_method!(self, can_extents), extents: opt_method!(self, extents), can_cache: opt_method!(self, can_cache), cache: opt_method!(self, cache), thread_model: opt_method!(self, thread_model), can_fast_zero: opt_method!(self, can_fast_zero), preconnect: opt_method!(self, preconnect), get_ready: opt_method!(self, get_ready) }; // Leak the memory to C. NBDKit will never give it back. Box::into_raw(Box::new(plugin)) } #[doc(hidden)] pub fn new() -> Builder { Builder::default() } } // C functions provided by the nbdkit binary // TODO: nbdkit_peer_name extern "C" { fn nbdkit_add_extent(extents: *mut c_void, offset: u64, length: u64, ty: u32) -> c_int; fn nbdkit_error(fmt: *const c_char, ...); fn nbdkit_export_name() -> *const c_char; fn nbdkit_set_error(errno: c_int); #[cfg(feature = "nix")] fn nbdkit_peer_name( addr: *mut libc::sockaddr, addrlen: *mut libc::socklen_t) -> c_int; fn nbdkit_shutdown(); fn nbdkit_stdio_safe() -> c_int; } /// Return the optional NBD export name if one was negotiated with the current /// client /// /// Note that this function must be called from one of nbdkit's own threads. /// That is, it can only be called in the same thread as one of the `Server` /// callbacks. pub fn export_name() -> std::result::Result<String, Box<dyn error::Error>> { unsafe { let p = nbdkit_export_name(); if p.is_null() { return Err("No export name available".into()); } CStr::from_ptr(p) }.to_str() .map(|s| s.to_owned()) .map_err(|e| Box::new(e) as Box<dyn error::Error>) } /// Is it safe to interact with stdin and stdout during the configuration phase? /// /// This function is only relevant up through `config_complete`. After the /// configuration phase, the client should assume that stdin and stdout have /// been closed. pub fn is_stdio_safe() -> bool { unsafe { nbdkit_stdio_safe() == 1 } } /// Return the peer (client) address, if available. /// /// Note that this function must be called from one of nbdkit's own threads. /// That is, it can only be called in the same thread as one of the `Server` /// callbacks. #[cfg(any(feature = "nix", all(feature = "nightly-docs", rustdoc)))] #[cfg_attr(feature = "nightly-docs", doc(cfg(feature = "nix")))] pub fn peername() -> std::result::Result<SockAddr, Box<dyn error::Error>> { let mut ss = mem::MaybeUninit::<libc::sockaddr_storage>::uninit(); let mut len = mem::size_of_val(&ss) as libc::socklen_t; unsafe { let sa = ss.as_mut_ptr() as *mut libc::sockaddr; let r = nbdkit_peer_name(sa, &mut len as *mut _); if r == -1 { // Note that nbdkit_peer_name does _not_ set errno return Err("No peer name available".into()); } sockaddr_storage_to_addr(&ss.assume_init(), len as usize) .map_err(|e| Box::new(e) as Box<dyn error::Error>) } } /// Request nbdkit to asynchronously and safely shutdown the server. pub fn shutdown() { unsafe { nbdkit_shutdown() }; } #[doc(hidden)] #[repr(C)] pub struct Plugin { // Do not modify these three fields directly. #[doc(hidden)] pub _struct_size: u64, #[doc(hidden)] pub _api_version: c_int, #[doc(hidden)] pub _thread_model: c_int, pub name: *const c_char, pub longname: *const c_char, pub version: *const c_char, pub description: *const c_char, pub load: Option<extern fn ()>, pub unload: Option<extern fn ()>, pub config: Option<extern fn (*const c_char, *const c_char) -> c_int>, pub config_complete: Option<extern fn () -> c_int>, pub config_help: *const c_char, pub open: extern fn (c_int) -> *mut c_void, pub close: extern fn (*mut c_void), pub get_size: extern fn (*mut c_void) -> i64, pub can_write: Option<extern fn (*mut c_void) -> c_int>, pub can_flush: Option<extern fn (*mut c_void) -> c_int>, pub is_rotational: Option<extern fn (*mut c_void) -> c_int>, pub can_trim: Option<extern fn (*mut c_void) -> c_int>, // Slots for old v1 API functions. #[doc(hidden)] pub _pread_v1: Option<extern fn ()>, #[doc(hidden)] pub _pwrite_v1: Option<extern fn ()>, #[doc(hidden)] pub _flush_v1: Option<extern fn ()>, #[doc(hidden)] pub _trim_v1: Option<extern fn ()>, #[doc(hidden)] pub _zero_v1: Option<extern fn ()>, #[doc(hidden)] pub errno_is_preserved: c_int, pub dump_plugin: Option<extern fn ()>, pub can_zero: Option<extern fn (*mut c_void) -> c_int>, pub can_fua: Option<extern fn (*mut c_void) -> c_int>, pub pread: extern fn (h: *mut c_void, buf: *mut c_char, count: u32, offset: u64, flags: u32) -> c_int, pub pwrite: Option<extern fn (h: *mut c_void, buf: *const c_char, count: u32, offset: u64, flags: u32) -> c_int>, pub flush: Option<extern fn (h: *mut c_void, flags: u32) -> c_int>, pub trim: Option<extern fn (h: *mut c_void, count: u32, offset: u64, flags: u32) -> c_int>, pub zero: Option<extern fn (h: *mut c_void, count: u32, offset: u64, flags: u32) -> c_int>, pub magic_config_key: *const c_char, pub can_multi_conn: Option<extern fn (h: *mut c_void) -> c_int>, pub can_extents: Option<extern fn (h: *mut c_void) -> c_int>, pub extents: Option<extern fn (h: *mut c_void, count: u32, offset: u64, rawflags: u32, extent_handle: *mut c_void) -> c_int>, pub can_cache: Option<extern fn (h: *mut c_void) -> c_int>, pub cache: Option<extern fn (h: *mut c_void, count: u32, offset: u64, flags: u32) -> c_int>, pub thread_model: Option<extern fn () -> c_int>, pub can_fast_zero: Option<extern fn (h: *mut c_void) -> c_int>, pub preconnect: Option<extern fn(readonly: c_int) -> c_int>, pub get_ready: Option<extern fn() -> c_int>, } /// Register your plugin with NBDKit. /// /// Declare which optional methods it supports by supplying each as an argument. /// /// # Examples /// /// ``` /// # use nbdkit::*; /// struct MyPlugin{ /// // ... /// } /// impl Server for MyPlugin { /// fn get_size(&self) -> Result<i64> { /// # unimplemented!(); /// // ... /// } /// /// fn name() -> &'static str { /// "my_plugin" /// } /// /// fn open(_readonly: bool) -> Box<dyn Server> { /// # unimplemented!(); /// // ... /// } /// /// fn read_at(&self, buf: &mut [u8], offs: u64) -> Result<()> { /// # unimplemented!(); /// // ... /// } /// fn write_at(&self, buf: &[u8], offs: u64, flags: Flags) -> Result<()> { /// # unimplemented!(); /// // ... /// } /// } /// /// plugin!(MyPlugin {write_at}); /// ``` #[macro_export] macro_rules! plugin { ( $cls:path { $($feat:ident),* } ) => { #[no_mangle] pub extern fn plugin_init () -> *const ::nbdkit::Plugin { let mut plugin = ::nbdkit::Builder::new(); $(plugin.$feat = true;)* plugin.into_ptr::<$cls>() } } } #[cfg(test)] mod t { #[cfg(feature = "nix")] mod peername { use super::super::*; use lazy_static::lazy_static; use mockall::{mock, predicate::*}; use std::sync::Mutex; lazy_static! { /// Mediates access to MockNbdkit's global expectations /// Any test that sets an expectation on a static method /// grab this mutex static ref MOCK_NBDKIT_MTX: Mutex<()> = Mutex::new(()); } mock! { pub Nbdkit { fn peer_name(addr: *mut libc::sockaddr, addrlen: *mut libc::socklen_t) -> c_int; } } #[no_mangle] extern fn nbdkit_peer_name( addr: *mut libc::sockaddr, addrlen: *mut libc::socklen_t) -> c_int { MockNbdkit::peer_name(addr, addrlen) } #[test] fn error() { let _m = MOCK_NBDKIT_MTX.lock().unwrap(); let ctx = MockNbdkit::peer_name_context(); ctx.expect() // Since nbdkit_peer_name does not set errno, all types of // errors are indistinguishable to a plugin .return_const(-1); let e = peername().unwrap_err(); ctx.checkpoint(); assert_eq!("No peer name available", e.to_string()); } #[test] fn in4() { let _m = MOCK_NBDKIT_MTX.lock().unwrap(); let ctx = MockNbdkit::peer_name_context(); ctx.expect() .withf(|_, len| { let l = unsafe {**len as usize}; l == mem::size_of::<libc::sockaddr_storage>() }).returning(|sa, sl| { let sin = sa as *mut libc::sockaddr_in; unsafe { *sin = libc::sockaddr_in { sin_family: libc::AF_INET as libc::sa_family_t, sin_port: u16::from_le_bytes([4, 0xd2]), sin_addr: libc::in_addr { s_addr: u32::from_le_bytes([127, 0, 0, 1]) }, .. mem::zeroed() }; *sl = mem::size_of::<libc::sockaddr_in>() as libc::socklen_t; } 0 }); assert_eq!("127.0.0.1:1234", peername().unwrap().to_str()); ctx.checkpoint(); } #[test] fn in6() { let _m = MOCK_NBDKIT_MTX.lock().unwrap(); let ctx = MockNbdkit::peer_name_context(); ctx.expect() .withf(|_, len| { let l = unsafe {**len as usize}; l == mem::size_of::<libc::sockaddr_storage>() }).returning(|sa, sl| { let sin6 = sa as *mut libc::sockaddr_in6; unsafe { *sin6 = libc::sockaddr_in6 { sin6_family: libc::AF_INET6 as libc::sa_family_t, sin6_port: u16::from_le_bytes([4, 0xd2]), sin6_addr: libc::in6_addr { s6_addr: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1], }, .. mem::zeroed() }; *sl = mem::size_of::<libc::sockaddr_in6>() as libc::socklen_t; } 0 }); assert_eq!("[::1]:1234", peername().unwrap().to_str()); ctx.checkpoint(); } #[test] fn un() { let _m = MOCK_NBDKIT_MTX.lock().unwrap(); let ctx = MockNbdkit::peer_name_context(); ctx.expect() .withf(|_, len| { let l = unsafe {**len as usize}; l == mem::size_of::<libc::sockaddr_storage>() }).returning(|sa, sl| { let sun = sa as *mut libc::sockaddr_un; unsafe { *sun = mem::zeroed(); (*sun).sun_family = libc::AF_UNIX as libc::sa_family_t; ptr::copy_nonoverlapping( b"/tmp/foo.sock\0".as_ptr() as *const i8, (*sun).sun_path.as_mut_ptr(), 14); *sl = mem::size_of::<libc::sockaddr_un>() as libc::socklen_t; } 0 }); assert_eq!("/tmp/foo.sock", peername().unwrap().to_str()); ctx.checkpoint(); } } }