qcow2

README

qcow2

Package qcow2 provides read-only access to qcow2 disk images, including images with deflate or zstd compression.

Documentation

Overview

Package qcow2 provides read-only access to qcow2 disk images, including images with deflate or zstd compression. Writing qcow2 images is not supported.

Index

• type Image
  • func Open(r io.ReaderAt) (*Image, error)
  • func (img *Image) ReadAt(p []byte, off int64) (int, error)
  • func (img *Image) Size() int64
• type Stats

Types

type Image

type Image struct {
	// Stats are incremented by the library during reads. Exporting
	// them to expvar, Prometheus, or other monitoring systems is
	// left to the caller.
	Stats
	// contains filtered or unexported fields
}

Image is a read-only qcow2 disk image. It implements io.ReaderAt over the virtual disk contents.

func Open

func Open(r io.ReaderAt) (*Image, error)

Open opens a qcow2 image for reading. The returned *Image is safe for concurrent use.

func (*Image) ReadAt

func (img *Image) ReadAt(p []byte, off int64) (int, error)

ReadAt reads from the virtual disk image at the given offset. It implements io.ReaderAt.

func (*Image) Size

func (img *Image) Size() int64

Size returns the virtual size of the disk image in bytes.

type Stats

type Stats struct {
	Reads              expvar.Int // number of ReadAt calls
	BytesRead          expvar.Int // total virtual bytes returned
	ClusterReads       expvar.Int // total cluster-level read operations
	ClusterHoles       expvar.Int // reads served from unallocated or zero clusters
	ClusterStandard    expvar.Int // reads served from standard (uncompressed) clusters
	ClusterCompressed  expvar.Int // reads served from compressed clusters
	L2CacheHits        expvar.Int // L2 table found in cache
	L2CacheMisses      expvar.Int // L2 table read from underlying reader
	L2CacheEvictions   expvar.Int // L2 cache full clears
	CompCacheHits      expvar.Int // decompressed cluster found in cache
	CompCacheMisses    expvar.Int // cluster required decompression
	CompCacheEvictions expvar.Int // decompressed cluster cache full clears
}

Stats contains counters for an Image. All fields are safe for concurrent access.