Commit 4f827280 authored by Matt Mooney's avatar Matt Mooney Committed by Linus Torvalds

Documentation: update kbuild loadable modules goals & examples

Update section 3.3 Loadable module goals - obj-m, from $(<module_name>-objs)
to $(<module_name>-y) for easier addition of conditional objects to the
module. The examples are also updated to reflect the current state of
each Makefile used.
Signed-off-by: default avatarmatt mooney <mfm@muteddisk.com>
Reviewed-by: default avatarWANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c7825cfa
......@@ -187,34 +187,35 @@ more details, with real examples.
Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm'
If a kernel module is built from several source files, you specify
that you want to build a module in the same way as above.
Kbuild needs to know which the parts that you want to build your
module from, so you have to tell it by setting an
$(<module_name>-objs) variable.
that you want to build a module in the same way as above; however,
kbuild needs to know which object files you want to build your
module from, so you have to tell it by setting a $(<module_name>-y)
variable.
Example:
#drivers/isdn/i4l/Makefile
obj-$(CONFIG_ISDN) += isdn.o
isdn-objs := isdn_net_lib.o isdn_v110.o isdn_common.o
obj-$(CONFIG_ISDN_I4L) += isdn.o
isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
In this example, the module name will be isdn.o. Kbuild will
compile the objects listed in $(isdn-objs) and then run
compile the objects listed in $(isdn-y) and then run
"$(LD) -r" on the list of these files to generate isdn.o.
Kbuild recognises objects used for composite objects by the suffix
-objs, and the suffix -y. This allows the Makefiles to use
the value of a CONFIG_ symbol to determine if an object is part
of a composite object.
Due to kbuild recognizing $(<module_name>-y) for composite objects,
you can use the value of a CONFIG_ symbol to optionally include an
object file as part of a composite object.
Example:
#fs/ext2/Makefile
obj-$(CONFIG_EXT2_FS) += ext2.o
ext2-y := balloc.o bitmap.o
ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
In this example, xattr.o is only part of the composite object
ext2.o if $(CONFIG_EXT2_FS_XATTR) evaluates to 'y'.
ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
namei.o super.o symlink.o
ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
xattr_trusted.o
In this example, xattr.o, xattr_user.o and xattr_trusted.o are only
part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR)
evaluates to 'y'.
Note: Of course, when you are building objects into the kernel,
the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
......
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