Re: [Libguestfs] [libnbd PATCH v4 11/11] rust: Add some examples

This patch adds a few examples in rust/examples/. The examples are compiled and run as part of the test suite. --- rust/Makefile.am | 3 + rust/examples/concurrent-read-write.rs | 135 +++++++++++++++++++++++++ rust/examples/connect-command.rs | 39 +++++++ rust/examples/fetch-first-sector.rs | 38 +++++++ rust/examples/get-size.rs | 29 ++++++ rust/run-tests.sh | 7 ++ 6 files changed, 251 insertions(+) create mode 100644 rust/examples/concurrent-read-write.rs create mode 100644 rust/examples/connect-command.rs create mode 100644 rust/examples/fetch-first-sector.rs create mode 100644 rust/examples/get-size.rs diff --git a/rust/Makefile.am b/rust/Makefile.am index b954b22..d75163d 100644 --- a/rust/Makefile.am +++ b/rust/Makefile.am @@ -32,6 +32,9 @@ source_files = \ src/types.rs \ src/utils.rs \ src/async_handle.rs \ + examples/connect-command.rs \ + examples/get-size.rs \ + examples/fetch-first-sector.rs \

libnbd-sys/Cargo.toml \ libnbd-sys/build.rs \ $(NULL) diff --git a/rust/examples/concurrent-read-write.rs b/rust/examples/concurrent-read-write.rs new file mode 100644 index 0000000..a1c3e8a --- /dev/null +++ b/rust/examples/concurrent-read-write.rs @@ -0,0 +1,135 @@ +//! Example usage with nbdkit: +//! +//! nbdkit -U - memory 100M \ +//! --run 'cargo run --example concurrent-read-write -- $unixsocket' +//! +//! This will read and write randomly over the first megabyte of the +//! plugin using multi-conn, multiple threads and multiple requests in +//! flight on each thread. + +#![deny(warnings)] +use rand::prelude::*; +use std::env; +use std::path::PathBuf; +use std::sync::Arc; +use tokio::task::JoinSet; + +/// Number of simultaneous connections to the NBD server. +/// +/// Note that some servers only support a limited number of +/// simultaneous connections, and/or have a configurable thread pool +/// internally, and if you exceed those limits then something will break. +const NR_MULTI_CONN: usize = 8; + +/// Number of commands that can be "in flight" at the same time on each +/// connection. (Therefore the total number of requests in flight may +/// be up to NR_MULTI_CONN * MAX_IN_FLIGHT). +const MAX_IN_FLIGHT: usize = 16; + +/// The size of large reads and writes, must be > 512. +const BUFFER_SIZE: usize = 1024; + +/// Number of commands we issue (per [task][tokio::task]). +const NR_CYCLES: usize = 32; + +/// Statistics gathered during the run. +#[derive(Debug, Default)] +struct Stats { + /// The total number of requests made. + requests: usize, +} + +#[tokio::main] +async fn main() -> anyhow::Result<()> { + let args = env::args_os().collect::<Vec<_>>(); + if args.len() != 2 { + anyhow::bail!("Usage: {:?} socket", args[0]); + } + let socket = &args[1]; + + // We begin by making a connection to the server to get the export size + // and ensure that it supports multiple connections and is writable. + let nbd = libnbd::Handle::new()?; + nbd.connect_unix(&socket)?; + let export_size = nbd.get_size()?; + anyhow::ensure!( + (BUFFER_SIZE as u64) < export_size, + "export is {export_size}B, must be larger than {BUFFER_SIZE}B" + ); + anyhow::ensure!( + !nbd.is_read_only()?, + "error: this NBD export is read-only" + ); + anyhow::ensure!( + nbd.can_multi_conn()?, + "error: this NBD export does not support multi-conn" + ); + drop(nbd); // Close the connection. + + // Start the worker tasks, one per connection. + let mut tasks = JoinSet::new(); + for i in 0..NR_MULTI_CONN { + tasks.spawn(run_thread(i, socket.clone().into(), export_size)); + } + + // Wait for the tasks to complete. + let mut stats = Stats::default(); + while !tasks.is_empty() { + let this_stats = tasks.join_next().await.unwrap().unwrap()?; + stats.requests += this_stats.requests; + } + + // Make sure the number of requests that were required matches what + // we expect. + assert_eq!(stats.requests, NR_MULTI_CONN * NR_CYCLES); + + Ok(()) +} + +async fn run_thread( + task_idx: usize, + socket: PathBuf, + export_size: u64, +) -> anyhow::Result<Stats> { + // Start a new connection to the server. + // We shall spawn many commands concurrently on different tasks and those + // futures must be `'static`, hence we wrap the handle in an [Arc]. + let nbd = Arc::new(libnbd::AsyncHandle::new()?); + nbd.connect_unix(socket).await?; + + let mut rng = SmallRng::seed_from_u64(44 as u64); + + // Issue commands. + let mut stats = Stats::default(); + let mut join_set = JoinSet::new(); + //tokio::time::sleep(std::time::Duration::from_secs(1)).await; + while stats.requests < NR_CYCLES || !join_set.is_empty() { + while stats.requests < NR_CYCLES && join_set.len() < MAX_IN_FLIGHT { + // If we want to issue another request, do so. Note that we reuse + // the same buffer for multiple in-flight requests. It doesn't + // matter here because we're just trying to write random stuff, + // but that would be Very Bad in a real application. + // Simulate a mix of large and small requests. + let size = if rng.gen() { BUFFER_SIZE } else { 512 }; + let offset = rng.gen_range(0..export_size - size as u64); + + let mut buf = [0u8; BUFFER_SIZE]; + let nbd = nbd.clone(); + if rng.gen() { + join_set.spawn(async move { + nbd.pread(&mut buf, offset, None).await + }); + } else { + // Fill the buf with random data. + rng.fill(&mut buf); + join_set + .spawn(async move { nbd.pwrite(&buf, offset, None).await }); + } + stats.requests += 1; + } + join_set.join_next().await.unwrap().unwrap()?; + } + + if task_idx == 0 {} + Ok(stats) +} diff --git a/rust/examples/connect-command.rs b/rust/examples/connect-command.rs new file mode 100644 index 0000000..db4adbe --- /dev/null +++ b/rust/examples/connect-command.rs @@ -0,0 +1,39 @@ +//! This example shows how to run an NBD server +//! (nbdkit) as a subprocess of libnbd. + + +fn main() -> libnbd::Result<()> { + // Create the libnbd handle. + let handle = libnbd::Handle::new()?; + + // Run nbdkit as a subprocess. + let args = [ + "nbdkit", + // You must use ‘-s’ (which tells nbdkit to serve + // a single connection on stdin/stdout). + "-s", + // It is recommended to use ‘--exit-with-parent’ + // to ensure nbdkit is always cleaned up even + // if the main program crashes. + "--exit-with-parent", + // Use this to enable nbdkit debugging. + "-v", + // The nbdkit plugin name - this is a RAM disk. + "memory", + "size=1M", + ]; + handle.connect_command(&args)?; + + // Write some random data to the first sector. + let wbuf: Vec<u8> = (0..512).into_iter().map(|i| (i % 13) as u8).collect(); + handle.pwrite(&wbuf, 0, None)?; + + // Read the first sector back. + let mut rbuf = [0; 512]; + handle.pread(&mut rbuf, 0, None)?; + + // What was read must be exactly the same as what was written. + assert_eq!(wbuf.as_slice(), rbuf.as_slice()); + + Ok(()) +} diff --git a/rust/examples/fetch-first-sector.rs b/rust/examples/fetch-first-sector.rs new file mode 100644 index 0000000..9efb47a --- /dev/null +++ b/rust/examples/fetch-first-sector.rs @@ -0,0 +1,38 @@ +//! This example shows how to connect to an NBD server +//! and fetch and print the first sector (usually the +//! boot sector or partition table or filesystem +//! superblock). +//! +//! You can test it with nbdkit like this: +//! +//! nbdkit -U - floppy . \ +//! --run 'cargo run --example fetch-first-sector -- $unixsocket' +//! +//! The nbdkit floppy plugin creates an MBR disk so the +//! first sector is the partition table. + +use pretty_hex::pretty_hex; +use std::env; + +fn main() -> anyhow::Result<()> { + let nbd = libnbd::Handle::new()?; + + let args = env::args_os().collect::<Vec<_>>(); + if args.len() != 2 { + anyhow::bail!("Usage: {:?} socket", args[0]); + } + let socket = &args[1]; + + // Connect to the NBD server over a + // Unix domain socket. + nbd.connect_unix(socket)?; + + // Read the first sector synchronously. + let mut buf = [0; 512]; + nbd.pread(&mut buf, 0, None)?; + + // Print the sector in hexdump like format. + print!("{}", pretty_hex(&buf)); + + Ok(()) +} diff --git a/rust/examples/get-size.rs b/rust/examples/get-size.rs new file mode 100644 index 0000000..7f31df5 --- /dev/null +++ b/rust/examples/get-size.rs @@ -0,0 +1,29 @@ +//! This example shows how to connect to an NBD +//! server and read the size of the disk. +//! +//! You can test it with nbdkit like this: +//! +//! nbdkit -U - memory 1M \ +//! --run 'cargo run --example get-size -- $unixsocket' + +use std::env; + +fn main() -> anyhow::Result<()> { + let nbd = libnbd::Handle::new()?; + + let args = env::args_os().collect::<Vec<_>>(); + if args.len() != 2 { + anyhow::bail!("Usage: {:?} socket", args[0]); + } + let socket = &args[1]; + + // Connect to the NBD server over a + // Unix domain socket. + nbd.connect_unix(socket)?; + + // Read the size in bytes and print it. + let size = nbd.get_size()?; + println!("{:?}: size = {size} bytes", socket); + + Ok(()) +} diff --git a/rust/run-tests.sh b/rust/run-tests.sh index da7852a..bdc0f16 100755 --- a/rust/run-tests.sh +++ b/rust/run-tests.sh @@ -25,6 +25,13 @@ requires nbdkit --version

if [ -z "$VG" ]; then $CARGO test -- --nocapture + $CARGO run --example connect-command + nbdkit -U - memory 1M \ + --run "$CARGO"' run --example get-size -- $unixsocket'

+ nbdkit -U - floppy . \ + --run "$CARGO"' run --example fetch-first-sector -- $unixsocket' + nbdkit -U - memory 10M \ + --run "$CARGO"' run --example concurrent-read-write -- $unixsocket' else $CARGO test --config "target.'cfg(all())'.runner = \"$VG\"" -- --nocapture fi -- 2.41.0