commit 71e7ec145b1a7fb55b7d272c0fc29d5ed81f3bb4
author Milton D. Miller II <miltonm@us.ibm.com> Wed Mar 02 18:28:54 2016 -0600
committer Milton D. Miller II <miltonm@us.ibm.com> Mon Mar 07 15:22:41 2016 -0600
tree 4b4858382d4f43a95c0d2d38d60ac6fc62ba05fd
parent 6d85431579a9d385a63a0f5b2f8cf6c6dd4f26e4

init: Add a hook to download files

Add a hook to download a read-only file system image file from
a URL using TFTP, HTTP, or FTP.  The URL is retrieved from a
u-boot environment variable unless the file is already in the
initramfs image.  Only execute this command if the previously
established options file has a keyword trigger.  Do not even
consider the option if a build option flag is not set to y,
and allow each protocol to be disabled by simiar build options.

This allows one to specify at u-boot commands that would download
a read-only file system into memory for execution this boot instead
of needing to create a custom initramfs to netboot or specifying
debug-init-sh, entering the password, and doing the download from
the shell.

Note: Access to set u-boot environment variables implys the
ability to replace the kernel and initramfs session.  Access to
the variables and the serial console likely gives full root access
to the system at this time.  The existing shutdown and update
scripts have paths that expose a root shell to the serial port
without a prior password challenge.

Signed-off-by: Milton Miller <miltonm@us.ibm.com>