block: qcow: Test compressed cluster read via QcowDiskSync

Write a known data pattern to a QCOW2 image, convert all allocated
clusters to compressed format using compress_allocated_clusters,
reopen the image through QcowDiskSync, and verify that reading back
the full cluster returns the original data.

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

block/src/qcow_sync.rs

@@ -448,6 +448,7 @@ mod unit_tests {
     use super::*;
     use crate::disk_file::{AsyncDiskFile, DiskSize, Resizable};
     use crate::qcow::{BackingFileConfig, ImageType, QcowFile, RawFile};
+    use crate::qcow_common::unit_tests::compress_allocated_clusters;
 
     fn create_disk_with_data(
         file_size: u64,
@@ -1933,4 +1934,20 @@ mod unit_tests {
         let abuf = AlignedBuf::new(513, 512).unwrap();
         assert_eq!(abuf.layout().size(), 1024);
     }
+
+    #[test]
+    fn test_compressed_read() {
+        let cluster_size = 65536usize;
+        let data: Vec<u8> = (0..=255).cycle().take(cluster_size).collect();
+        let (temp, disk) = create_disk_with_data(100 * 1024 * 1024, &data, 0, false, false);
+        drop(disk);
+
+        compress_allocated_clusters(&mut temp.as_file().try_clone().unwrap());
+
+        let disk =
+            QcowDiskSync::new(temp.as_file().try_clone().unwrap(), false, false, false).unwrap();
+
+        let buf = async_read(&disk, 0, cluster_size);
+        assert_eq!(buf, data);
+    }
 }