multiple definiton of function-error in kernel-file

Hey guys. What I'm currently trying to do is to port the tool DigSig to a Cen开发者_如何转开发tOS-Kernel which seems to lack a few important crypto-functions for DigSig. So the port this I just a newer /linux/crypto.h which has the functionality I need plus I added this little code:

void kzfree(const void *p) {
    size_t ks;
    void *mem = (void *)p;

    if (unlikely(ZONP(mem)))
             return;
    ks = ksize(mem);
    memset(mem, 0, ks);
    kfree(mem);

}

because my kernel I'm working on does not have kzfree yet. Now, when I try to compile DigSig, this is the output:

/home/Chris/dsTest/dsi_sysfs.o: In function `kzfree':
/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: multiple definition of `kzfree'
/home/Chris/dsTest/digsig.o:/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: first defined here
/home/Chris/dsTest/digsig_cache.o: In function `kzfree':
/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: multiple definition of `kzfree'
/home/Chris/dsTest/digsig.o:/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: first defined here
/home/Chris/dsTest/digsig_revocation.o: In function `kzfree':
/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: multiple definition of `kzfree'
/home/Chris/dsTest/digsig.o:/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: first defined here
/home/Chris/dsTest/dsi_sig_verify.o: In function `kzfree':
/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: multiple definition of `kzfree'
/home/Chris/dsTest/digsig.o:/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h:114: first defined here

Of course, all is covered by #ifndef-Guards, so I just cannot understand why he is defining this function multiple times... Any ideas?

Your include file gets included in multiple places. This is not compile time error. But rather a linked time error. Each of your file got compiled and produced following .o files

/home/Chris/dsTest/dsi_sysfs.o
/home/Chris/dsTest/digsig_cache.o
/home/Chris/dsTest/digsig_revocation.o
/home/Chris/dsTest/dsi_sig_verify.o

Now while linking them together it finds multiple definition of kzfreez, one each in above .o files because their corresponding c files included

/usr/src/kernels/2.6.18-194.32.1.el5-i686/include/linux/crypto.h

You have ifdef guarded the file, but that only prevents inclusion of .h file in same c file (translation units) not across different c files.

You should write the function in c file and add in in make files, so that it gets compiled separately and linked. And only add declaration in crypto.h . (For testing you can add definition in crypto.c and declaration in crypto.h).