feature pipeline

Feature: pipeline

The feature calls the pipe elements one by one and passes them the results of the previous elements.

This feature is intended for boot scenarios not related to simple disk initialization. Normal disk loading can also be done using pipeline (see examples).

To activate a pipeline, you must specify it as root=pipeline in the boot cmdline. The sequence of steps is specified in the pipeline=... parameter.

Pipe elements

• getimage receives and mounts the remote image.
• mountfs mounts file from the previous pipe element.
• overlayfs combines one or more pipe elements using overlayfs.
• waitdev waits for the local device to appear.
• rootfs uses the result of the previous element as a root.
• wait-resume is waiting for the resume attempt to complete. This step is necessary to avoid race conditions between disk initialization for resume and pipeline.

Boot parameters

• pipeline=name[,name1][,name2] - the main parameter that determines the order in which pipe elements are called.
• getimage specifies an URL to fetch and mount.
• mountfs specifies a file to mount.
• overlayfs defines a list of elements to be combined.
• waitdev describes the local device to wait. The format of this parameter is the same as root=.

The separator between the elements is a comma (,).

The parameters can be specified more than once depending on how many times a corresponding element is mentioned in the pipeline.

Example

Simple boot.

Cmdline: root=pipeline pipeline=waitdev,mountfs,rootfs waitdev=LABEL=MYROOT mountfs=dev

Using these parameters, the pipeline will wait for a device with the "MYROOT" label, mount it, and boot from it.

Network boot

Cmdline: root=pipeline pipeline=getimage,mountfs,overlayfs,rootfs getimage=http://ftp.altlinux.org/pub/people/mike/iso/misc/vi-20140918-i586.iso mountfs=rescue

Following these parameters, the pipeline downloads the vi-20140918-i586.iso image, mount it as a loop, make it writable using overlayfs and will try to boot from it.