453552c838
This backend uses the overlayfs union filesystem for containers plus hard link file sharing for images. Each container/image can have a "root" subdirectory which is a plain filesystem hierarchy, or they can use overlayfs. If they use overlayfs there is a "upper" directory and a "lower-id" file, as well as "merged" and "work" directories. The "upper" directory has the upper layer of the overlay, and "lower-id" contains the id of the parent whose "root" directory shall be used as the lower layer in the overlay. The overlay itself is mounted in the "merged" directory, and the "work" dir is needed for overlayfs to work. When a overlay layer is created there are two cases, either the parent has a "root" dir, then we start out with a empty "upper" directory overlaid on the parents root. This is typically the case with the init layer of a container which is based on an image. If there is no "root" in the parent, we inherit the lower-id from the parent and start by making a copy if the parents "upper" dir. This is typically the case for a container layer which copies its parent -init upper layer. Additionally we also have a custom implementation of ApplyLayer which makes a recursive copy of the parent "root" layer using hardlinks to share file data, and then applies the layer on top of that. This means all chile images share file (but not directory) data with the parent. Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson) |
||
|---|---|---|
| .. | ||
| copy.go | ||
| overlayfs.go | ||
| overlayfs_test.go | ||