Volume and Mount

Definitions

• Volume — a named, daemon-managed entity backed by a driver. Default driver is local; plugins add others.
• Mount — a per-container request: bind, volume, or tmpfs. --mount and the legacy -v syntaxes both produce the same internal struct.

Wire types

In api/types/volume/:

Type	Purpose
Volume	docker volume inspect payload.
CreateOptions	POST /volumes/create body.
ListResponse	GET /volumes.
ClusterVolume*	CSI volumes managed by swarm.

In api/types/mount/:

Type	Purpose
Mount	--mount spec; covers bind, volume, tmpfs, npipe, image, cluster.
BindOptions, VolumeOptions, TmpfsOptions, ImageOptions	Per-type extras.

Internal types

Object	File
Volume	daemon/volume/volume.go
MountPoint	daemon/volume/mounts/mounts.go
Driver	daemon/volume/volume.go
VolumesService	daemon/volume/service/service.go

Mount resolution

Parsing happens in daemon/volume/mounts/parser.go (Linux) and friends. The result is a MountPoint per request, with type, source path, destination, mode, and driver options. At container start, the daemon walks MountPoints:

• Bind mounts → check the host path exists, optionally chowning for userns.
• Named volumes → call Driver.Get(name) to obtain a host path.
• Tmpfs → just record the size/mode for the OCI spec.

The list is then translated into OCI mount spec entries by daemon/oci_linux.go.

Refcounting

The volumes service tracks how many containers reference a given volume; docker volume rm fails on a volume in use. Implementation in daemon/volume/service/.

See also

• Volumes for the full subsystem.
• Container for how mounts attach to a container.