We already have seen some variables in Device parameters. But there is more to variables.
global device is a special purpose device. It only exists as a
storage for global variables. Some global variables are created internally
in barebox (see Magic variables). Additional variables can be created with
the global - create or set global variables command:
This creates the
global.myvar variable which now can be used like any
other variable. You can also directly assign a value during creation:
NOTE: creating a variable with
global myvar1=foobar looks very similar
to assigning a value with
global.myvar1=foobar, but the latter fails when
a variable has not been created before.
1.7.2. Non volatile variables¶
Additionally to global variables barebox also has non volatile (nv) variables. Unlike the global variables the config variables are persistent over reboots.
Each nv variable is linked with the global variable of the same name. Whenever the nv variable changes its value the corresponding global variable also changes its value. The other way round though is not true: Changing a global variable does not change the corresponding nv variable. This means that changing a global variable changes the behaviour for the currently running barebox, while changing a nv variable changes the behaviour persistently over reboots.
nv variables can be created or removed with the nv - create, set or remove non volatile (NV) variables command.
The nv variables are made persistent using the environment facilities of barebox. They are saved automatically to the storage medium whenever barebox shuts down (that is, a reset - perform RESET of the CPU is issued or a kernel is started).
barebox@Phytec phyCARD-i.MX27:/ devinfo nv barebox@Phytec phyCARD-i.MX27:/ nv model=myboard barebox@myboard:/ devinfo nv Parameters: model: myboard barebox@myboard:/ devinfo global Parameters: [...] model: myboard [...] barebox@myboard:/ global.model=yourboard barebox@yourboard:/ devinfo nv Parameters: model: myboard barebox@yourboard:/
1.7.3. Non volatile device variables¶
Non volatile device variables are used to make device parameters persistent. They are regular nv variables but are linked with other devices instead of the global device. Every nv variable in the form nv.dev.<devname>.<paramname> will be mirrored to the corresponding <devname>.<paramname> variable.
This example changes the partitioning of the nand0 device:
barebox@Phytec phyCARD-i.MX27:/ nv dev.nand0.partitions: 4M(barebox),1M(barebox-environment),-(root) barebox@Phytec phyCARD-i.MX27:/ devinfo nand0 Parameters: [...] partitions: 4M(barebox),1M(barebox-environment),8M(kernel),1011M(root) [...]
1.7.4. Magic variables¶
Some variables have special meanings and influence the behaviour of barebox. Most but not all of them are consolidated in the The global device. Since it’s hard to remember which variables these are and if the current barebox has support for them the magicvar - list information about magic variables command can print a list of all variables with special meaning along with a short description:
barebox:/ magicvar OPTARG optarg for hush builtin getopt PATH colon separated list of paths to search for executables PS1 hush prompt armlinux_architecture ARM machine ID armlinux_system_rev ARM system revision armlinux_system_serial ARM system serial automount_path mountpath passed to automount scripts bootargs Linux Kernel parameters bootsource The source barebox has been booted from bootsource_instance The instance of the source barebox has been booted from global.boot.default default boot order ...