Linux Kernel Module - Producing two modules with shared local header

Question

I have the following files: buffer.c , buffer.h , chardevin.c , chardevout.c and Makefile . Both chardevin.c and chardevout.c are kernel modules. Both kernel modules include buffer.h , which is implemented by buffer.c . Ideally, I'd like the makefile to make both kernel modules while linking the buffer implementation (ie produce chardevin.ko and chardevout.ko). I can't seem to figure this part out...

Here's the contents of my Makefile :

obj-m += chardevin.o chardevout.o
obj-y += buffer.c

all:
    make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules

I get the following as output, however:

kylemart@ubuntu:/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex$ make
make -C /lib/modules/4.4.0-31-generic/build/ M=/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex modules
make[1]: Entering directory `/usr/src/linux-headers-4.4.0-31-generic'
  CC [M]  /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.o
  CC [M]  /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.o
  Building modules, stage 2.
  MODPOST 2 modules
WARNING: "buffer_read" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.ko] undefined!
WARNING: "buffer_length" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.ko] undefined!
WARNING: "buffer_write" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.ko] undefined!
WARNING: "buffer_length" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.ko] undefined!
  CC      /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.mod.o
  LD [M]  /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.ko
  CC      /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.mod.o
  LD [M]  /mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.ko
make[1]: Leaving directory `/usr/src/linux-headers-4.4.0-31-generic' 

Here's the contents of buffer.h :

#ifndef BUFFER_H
#define BUFFER_H

ssize_t buffer_write(const char *src, size_t n);
ssize_t buffer_read(char *dest, size_t n);
size_t buffer_length(void);

#endif 

What am I doing wrong?

EDIT:

Changed "buffer.c" to "buffer.o" in the Makefile. Here's the output:

kylemart@ubuntu:/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex$ make
make -C /lib/modules/4.4.0-31-generic/build/ M=/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex modules
make[1]: Entering directory `/usr/src/linux-headers-4.4.0-31-generic'
  Building modules, stage 2.
  MODPOST 2 modules
WARNING: "buffer_read" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.ko] undefined!
WARNING: "buffer_length" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevout.ko] undefined!
WARNING: "buffer_write" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.ko] undefined!
WARNING: "buffer_length" [/mnt/hgfs/ucf-os-linux/SplitDriverWithMutex/chardevin.ko] undefined!
make[1]: Leaving directory `/usr/src/linux-headers-4.4.0-31-generic' 

Answer 1

替换为以下内容：

obj-y += buffer.c -- > obj-y += buffer.o