Anatol Belski 5504ad753a block: qcow: Move compressed read decompression out of lock ...

Move decompression of compressed QCOW2 clusters out of the metadata
lock. Previously, reading a compressed cluster acquired a write lock
on metadata to perform in place decompression. Now, try_map_read
extracts the compressed layout (host offset, size) under a read lock
and returns it in the ClusterReadMapping::Compressed variant. Each
consumer (QcowSync, QcowAsync, Qcow2Backing, QcowFile) performs the
pread and decompression at the call site without holding any lock,
using the pread_alloc and decompress_cluster helpers.

Create the decoder once in QcowMetadata as Arc<dyn Decoder> and
share it via Arc::clone to QcowAsync, QcowSync, and Qcow2Backing
at construction time. This avoids per read RwLock acquisitions and
heap allocations. Add Send + Sync bounds to the Decoder trait.

This eliminates write lock contention on compressed reads, allowing
them to proceed concurrently with other read operations.

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

2026-04-20 18:09:12 +00:00

..

src

block: qcow: Move compressed read decompression out of lock

2026-04-20 18:09:12 +00:00

Cargo.toml

misc: make MSRV workspace-wide for cloud-hypervisor dependencies

2026-03-13 01:30:25 +00:00