util

Documentation

Index

• type AtomicWriter
  • func NewAtomicWriter(targetDir string, logContext string) (*AtomicWriter, error)
  • func (w *AtomicWriter) Write(payload map[string]FileProjection, setPerms func(subPath string) error) error
• type FileProjection

Types

type AtomicWriter

type AtomicWriter struct {
	// contains filtered or unexported fields
}

AtomicWriter handles atomically projecting content for a set of files into a target directory.

Note:

1. AtomicWriter reserves the set of pathnames starting with `..`.
2. AtomicWriter offers no concurrency guarantees and must be synchronized by the caller.

The visible files in this volume are symlinks to files in the writer's data directory. Actual files are stored in a hidden timestamped directory which is symlinked to by the data directory. The timestamped directory and data directory symlink are created in the writer's target dir. This scheme allows the files to be atomically updated by changing the target of the data directory symlink.

Consumers of the target directory can monitor the ..data symlink using inotify or fanotify to receive events when the content in the volume is updated.

func NewAtomicWriter

func NewAtomicWriter(targetDir string, logContext string) (*AtomicWriter, error)

NewAtomicWriter creates a new AtomicWriter configured to write to the given target directory, or returns an error if the target directory does not exist.

func (*AtomicWriter) Write

func (w *AtomicWriter) Write(payload map[string]FileProjection, setPerms func(subPath string) error) error

Write does an atomic projection of the given payload into the writer's target directory. Input paths must not begin with '..'. setPerms is an optional pointer to a function that caller can provide to set the permissions of the newly created files before they are published. The function is passed subPath which is the name of the timestamped directory that was created under target directory.

The Write algorithm is:

1. The payload is validated; if the payload is invalid, the function returns

2. The current timestamped directory is detected by reading the data directory symlink

3. The old version of the volume is walked to determine whether any portion of the payload was deleted and is still present on disk.

4. The data in the current timestamped directory is compared to the projected data to determine if an update to data directory is required.

5. A new timestamped dir is created if an update is required.

6. The payload is written to the new timestamped directory.

7. Permissions are set (if setPerms is not nil) on the new timestamped directory and files.

8. A symlink to the new timestamped directory ..data_tmp is created that will become the new data directory.

9. The new data directory symlink is renamed to the data directory; rename is atomic.

10. Symlinks and directory for new user-visible files are created (if needed).

    For example, consider the files: <target-dir>/podName <target-dir>/user/labels <target-dir>/k8s/annotations

    The user visible files are symbolic links into the internal data directory: <target-dir>/podName -> ..data/podName <target-dir>/usr -> ..data/usr <target-dir>/k8s -> ..data/k8s

    The data directory itself is a link to a timestamped directory with the real data: <target-dir>/..data -> ..2016_02_01_15_04_05.12345678/ NOTE(claudiub): We need to create these symlinks AFTER we've finished creating and linking everything else. On Windows, if a target does not exist, the created symlink will not work properly if the target ends up being a directory.

11. Old paths are removed from the user-visible portion of the target directory.

12. The previous timestamped directory is removed, if it exists.

type FileProjection

type FileProjection struct {
	Data   []byte
	Mode   int32
	FsUser *int64
}

FileProjection contains file Data and access Mode