blspec: fix documention of blspec_scan_directory's return code ...

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: Make error message more clear ...

"Nothing found on" is a bit unspecific. Make clear that no
bootspec entry is found.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: make cdev optional ...

the cdev for a given directory can be determined by get_cdev_by_mountpath().
Use this function and remove the cdev argument from blspec_scan_directory().
Also, export the function to make code possible which boots the bootloader
spec entries found in directories.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: Let scan functions return the number of entries found ...

So that callers can detect whether entries are found or not.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: Allow to boot partitions ...

Instead of only allowing complete devices we now also allow single
partitions to look for bootloader spec entries.

Normally the bootloader spec defines a way to find a partition containing /boot
on a device.  On embedded systems it's often useful instead to have only a
single partition image which contains both the kernel and the root filesystems.
This partition image may be written to the device multiple times. With this
patch they can be booted with 'boot emmc0.<partno>'

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: rename _hwdevice functions to _devicename ...

Since it's not necessarily the hardware device this seems to
be a more appropriate name.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: Push device_detect into blspec_scan_device ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

blspec: Fix once/default booting ...

The default/once files contain the full path to the entries, not
only the filename. This fixes booting the once and default entries.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Implement bootloader spec support for barebox ...

The Bootloader Specification describes a way how kernels can
be installed on devices and how they can be started by the bootloader.

The bootloader spec is currently supported by (x86) gummiboot and
by systemd which provides a kernel-install script. With the bootloader
spec it's possible for the Operating system to install a new kernel
without knowing about the bootloader and for the bootloader it's possible
to discover and start Operating Systems on a media without being
configured.

For more details about the spec see:

http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/

This patch adds barebox support for the spec. It enhances the 'boot'
command so that not only boot script names can be given, but also
devices containing bootloader spec entries. With this it's possible
to call the 'boot' command like: 'boot sd emmc net'. It would then
first look for bootloader spec entries on the (removable) sd card,
then, is nothing is found, on the internal emmc and if still
unsuccessful would call the 'net' bootscript.

The bootloader Spec currently doesn't specify which entry should be
default if multiple entries are found on a single device. Therefore
barebox currently has two extensions of the spec. The $BOOT diretory
can contain a file named 'default'. If present, the content of the
file is treated as a filename under $BOOT/loader/entries/ which is
used as default. Similarly if a file named 'once' is present, the
entry is started once and the file is removed afterwards. This is
useful for testing if a newly installed kernel works before making
it the default.

As on ARM and other Architectures a devicetree has to be specified
for the kernel, the 'devicetree' property is used to specify a
devicetree. Like 'kernel' and 'initrd' this also contains a pth
relative to $BOOT.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>