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doc:devel:dependencies

Using Dependencies

Topic

A typical package Makefile will contain a section like:

define Package/tcpdump/default
  SECTION:=net
  CATEGORY:=Network
  DEPENDS:=+libpcap
  TITLE:=Network monitoring and data acquisition tool
  URL:=http://www.tcpdump.org/
endef

This page talks about what the DEPENDS:= line should look like.

Dependency types

  • If you specify a package name without any ornaments then that means that the current package cannot be selected unless the package named in enabled. e.g., in tcpdump above,

DEPENDS:=libpcap

would mean that tcpdump would not be shown as possible to be selected unless libpcap were already selected

  • If you say +package that means if the current package is selected, it will cause package to be selected. This is the case with tcpdump above. It says that if tcpdump is selected, then select libpcap. e.g.

DEPENDS:=+libpcap

  • If you say +PACKAGE_packageb:packagec, it means that packagec will only get selected by the current package (e.g. tcpdump) if packageb is enabled. e.g.

DEPENDS:=+PACKAGE_arpd:libpcap
would mean that if tcpdump was selected, then if arpd was also selected, select libpcap.

Useful is the negation ! to only select a Package if it's not build into busybox

DEPENDS:=+!BUSYBOX_CONFIG_HOSTNAME:net-tools-hostname
This means select net-tools-hostname only if hostname is not build into busybox. But don't try it the other way around, see the last case.

  • If you say @SYMBOL that means that CONFIG_SYMBOL must be defined by OpenWRT in order for the package to be available for selection. e.g

DEPENDS:=@USB_SUPPORT
would mean that the package wouldn't even appear unless config symbol CONFIG_USB_SUPPORT was defined, for example by the package usb-core

  • If you say +@SYMBOL that means if the current package is selected, it will cause CONFIG_SYMBOL to be selected.

DEPENDS:=+@KERNEL_DEBUG_FS
would mean that the if you select the package, it would automatically set the config symbol CONFIG_KERNEL_DEBUG_FS. Beware: This works while compiling your own image. If you install this package on a running box with opkg, this dependency is not checked!

  • Don't be so clever and combine everything:

DEPENDS:=+@!PACKAGE_net-tools-hostname:BUSYBOX_CONFIG_HOSTNAME
Here we select the Symbol BUSYBOX_CONFIG_HOSTNAME if the package net-tools-hostname is not selected. The @ belongs to BUSYBOX_CONFIG_HOSTNAME. This works while compiling your own image, but the resulting ipkg depends on the unresolvable BUSYBOX_CONFIG_HOSTNAME, so your package cannot be installed later on a box with opkg.

As busybox can never be extended on a working box, always select an installable package when a busybox applet is not selected.

DEPENDS:=+!BUSYBOX_CONFIG_HOSTNAME:net-tools-hostname

Special Notes

It is possible to do select and depend on packages outside the usual DEPENDS definition. If, in the package Makefile, you have a definition:

define Package/package-name/config
    ...config stuff
endef
then you can include the following directives.

Directive Meaning
select package Selects a package if this package is selected
select package if packageb Selects a package if packageb is selected as well as this package
select package if SYMBOL Selects a package if CONFIG_SYMBOL is defined
depends packageb This package depends on packageb (i.e. won't even show up, unless packageb is selected)
depends packageb if packagec This package depends on packageb if packagec is selected
select SYMBOL Sets a symbol to y if this package is selected (.e.g. select BUSYBOX_FEATURE_MKSWAP_UUID)
select SYMBOL if packageb Like select SYMBOL but only if packageb is selected
select SYMBOL if SYMBOL2 Like select SYMBOL but only if SYMBOL2 is defined

The author is not aware of the ability to do depends SYMBOL.

Note that the if directives may also include &&, ||, !, and uses parentheses () to use logical expression for AND (&&), OR (||) and NOT (!), and for order of operations ('()').

There is also a default 'y' SYMBOL directive but the author is hazy on the details.

Caveats

Dependencies MAY NOT be circular (i.e. Package A may not depend on Package B, which in turn depends on Package A). If a circular dependency is created (whether directly or through another package), strange make menuconfig behaviour will be the result.

Bugs

There may be bugs in the OpenWRT build system wrt to dependencies. If you can confirm that you have a dependency problem, please report a bug. The developers would appreciate the following information:

  • the relevant portions of $ROOTDIR/tmp/.config-package.in (where $ROOTDIR is your OpenWRT source root dir)

NB Many apparent bugs are caused by circular dependencies. The openwrt build system doesn't like circular dependencies.

doc/devel/dependencies.txt · Last modified: 2013/01/05 03:03 by the2masters