[Libguestfs] [libnbd PATCH v4 11/11] rust: Add some examples
Tage Johansson
tage.j.lists at posteo.net
Wed Aug 2 12:40:56 UTC 2023
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
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