performance-metrics: Add QCOW2 tempfile helpers

Add qcow_tempfile() which creates a QCOW2 v3 image with all clusters
allocated via QcowFile::new plus sequential writes, then reopens it
as QcowDiskSync. Add QCOW_CLUSTER_SIZE constant for the default
64 KiB cluster size.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

performance-metrics/src/util.rs

@@ -4,14 +4,18 @@
 
 //! Shared benchmark helpers.
 
-use std::io::ErrorKind;
+use std::io::{ErrorKind, Seek, SeekFrom, Write};
 use std::thread;
 use std::time::Duration;
 
+use block::qcow::{QcowFile, RawFile};
+use block::qcow_async::QcowDiskAsync;
+use block::qcow_sync::QcowDiskSync;
 use vmm_sys_util::eventfd::EventFd;
 use vmm_sys_util::tempfile::TempFile;
 
 pub const BLOCK_SIZE: u64 = 4096;
+pub const QCOW_CLUSTER_SIZE: u64 = 65536;
 
 /// Create a temporary file pre sized to hold `num_blocks` blocks.
 pub fn sized_tempfile(num_blocks: usize) -> TempFile {
@@ -22,6 +26,45 @@ pub fn sized_tempfile(num_blocks: usize) -> TempFile {
     tmp
 }
 
+/// Create a QCOW2 image with `num_clusters` allocated clusters and return
+/// the tempfile handle.
+///
+/// Each cluster is default QCOW2 cluster size of 64 KiB. The image is
+/// created via `QcowFile::new` then populated with writes so that the
+/// clusters are actually allocated in the L2 / refcount tables.
+fn create_qcow_tempfile(num_clusters: usize) -> TempFile {
+    let tmp = TempFile::new().expect("failed to create tempfile");
+    let virtual_size = QCOW_CLUSTER_SIZE * num_clusters as u64;
+    let raw = RawFile::new(tmp.as_file().try_clone().unwrap(), false);
+    let mut qcow = QcowFile::new(raw, 3, virtual_size, true).expect("failed to create QCOW2 file");
+    let buf = vec![0xA5u8; QCOW_CLUSTER_SIZE as usize];
+    for i in 0..num_clusters {
+        qcow.seek(SeekFrom::Start(i as u64 * QCOW_CLUSTER_SIZE))
+            .expect("seek failed");
+        qcow.write_all(&buf).expect("write failed");
+    }
+    qcow.flush().expect("flush failed");
+    tmp
+}
+
+/// Create a QCOW2 image with `num_clusters` allocated clusters opened
+/// via `QcowDiskSync` (blocking I/O backend).
+pub fn qcow_tempfile(num_clusters: usize) -> (TempFile, QcowDiskSync) {
+    let tmp = create_qcow_tempfile(num_clusters);
+    let disk = QcowDiskSync::new(tmp.as_file().try_clone().unwrap(), false, false, true)
+        .expect("failed to open QCOW2 via QcowDiskSync");
+    (tmp, disk)
+}
+
+/// Create a QCOW2 image with `num_clusters` allocated clusters opened
+/// via `QcowDiskAsync` (io_uring backend).
+pub fn qcow_async_tempfile(num_clusters: usize) -> (TempFile, QcowDiskAsync) {
+    let tmp = create_qcow_tempfile(num_clusters);
+    let disk = QcowDiskAsync::new(tmp.as_file().try_clone().unwrap(), false, false, true)
+        .expect("failed to open QCOW2 via QcowDiskAsync");
+    (tmp, disk)
+}
+
 /// Spin and wait until the given eventfd becomes readable.
 pub fn wait_for_eventfd(notifier: &EventFd) {
     loop {