Function shared_backing_from

block/src/qcow/backing.rs:150–184

Construct a thread safe backing file reader.

(bf: BackingFile)

/// Construct a thread safe backing file reader.
pub fn shared_backing_from(bf: BackingFile) -> BlockResult<Arc<dyn BackingRead>> {
    let (kind, virtual_size) = bf.into_kind();

    let dup_fd = |fd: BorrowedFd<'_>| -> BlockResult<OwnedFd> {
        fd.try_clone_to_owned().map_err(|e| {
            BlockError::new(
                BlockErrorKind::Io,
                QcowError::BackingFileIo(String::new(), e),
            )
            .with_op(ErrorOp::DupBackingFd)
        })
    };

    match kind {
        BackingKind::Raw(raw_file) => {
            let fd = dup_fd(raw_file.as_fd())?;
            Ok(Arc::new(RawBacking { fd, virtual_size }))
        }
        BackingKind::Qcow { inner, backing } => {
            let data_fd = dup_fd(inner.raw_file.as_fd())?;
            let metadata = Arc::new(QcowMetadata::new(*inner));
            Ok(Arc::new(Qcow2Backing {
                cluster_size: metadata.cluster_size(),
                decoder: metadata.decoder(),
                metadata,
                data_fd,
                backing_file: backing.map(|bf| shared_backing_from(*bf)).transpose()?,
            }))
        }
        #[cfg(test)]
        BackingKind::QcowFile(_) => {
            unreachable!("QcowFile variant is only used by set_backing_file() in tests")
        }
    }
}