extern in C
Deepak Saxena
deepak@csociety.purdue.edu
Wed, 7 Mar 2001 01:56:05 -0500
FYI, do a 'man 7 arp' to get docs on the existing ioclt interface.
~Deepak
On Mar 07 2001, at 01:48, Deepak Saxena was caught saying:
>
> I'm assuming that demo.c is a user space prog? If so, there is _no_ possible
> way for it to call add_to_cache directly. add_to_cache is in the kernel
> symbol table, it can only be called by kernel functions. To call it from
> user space, you need to either:
>
> - Add a system call
> This is HIGHLY NOT recomended unless the function is extremely speed
> sensitive. From the function name, I'm assuming no.
> - Provide a device/driver specific ioctl that is accessed through a /dev
> entry
> - Provide an entry in /proc that can be write()n to for changing parameters.
> - Provide a sysctl() interface
>
> In all of the above cases, you can, and I highly reccomend you do, create
> a user space library wrapper add_to_cache function that performs the actual
> kernel call to abstract your users from the low level details.
>
> If demo.c is meant to be run by the kernel, you have to build it, but
> not attempt to link it and than insmod the resulting .o into the kernel
> and have the init_module() function do the magic.
>
> BTW, it looks like you're writing code to add something to the kernel
> ARP cache from user space. If that's what you want to do, this already
> exists. I ran the following
>
> /sbin/arp -s 192.168.0.40 00:10:20:30:40:51
>
> And did an strace (output attached). If you create a socket and do
> a SIOCSARP on it, you can alter the arp table from user space. Again,
> a add_to_cache() library call that wraps this is probably the best
> way to go.
>
> ~Deepak
>
> On Mar 06 2001, at 16:19, Brad Bonkoski was caught saying:
> > Hello,
> >
> > I have a large project in which I have multiple .c files that I am
> > making a Linux Module out of. I am trying to create an API for it, and
> > thought that an easy way would be to extern some of the functions that I
> > would allow "users" to include in their programs. I thought I good
> > place to start is to make a demo package of the functionality, or make a
> > program myself using the *API*
> > So, the grunt of it:
> >
> > I have three basic files that need to be used:
> > demo.c --> which calls the function add_to_cache( )
> > api.h --> which has the function prototype: extern int add_to_cache(
> > MAC_Value, IP_ADDR)
> > arp.c --> which has the function definition of add_to_cache( )
> >
> > so, arp.c is part of the actual module, which builds and registers with
> > Linux.
> >
> > Then I try to build demo.c seperately, linking only with the header file
> > (api.h) which is also included in arp.c
> > When compiling demo.c I get a linking error from 'ld' which says that
> > add_to_cache is an unresolved symbol.
> > What am I doing wrong? when running "ksyms" the function appears to be
> > registered, so should it link, or is there somethine else I should do?
> >
> > Any help would be appreciated.
> > Thanks,
> > Brad
> >
> >
> > _______________________________________________
> > Plug-devel mailing list - Plug-devel@lists.PLUG.phoenix.az.us
> > http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-devel
>
> --
> Deepak Saxena - deepak@csociety.purdue.edu - phone://602.790.0500
>
> call me 'evil' call me 'tide is on your side' anything that you want
> anybody knows you can conjure anything by the dark of the moon
> - Tori Amos, "Suede"
> execve("/sbin/arp", ["/sbin/arp", "-s", "192.168.0.40", "00:10:20:30:40:51"], [/* 25 vars */]) = 0
> brk(0) = 0x805230c
> old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40014000
> open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory)
> open("/etc/ld.so.cache", O_RDONLY) = 3
> fstat(3, {st_mode=S_IFREG|0644, st_size=26453, ...}) = 0
> old_mmap(NULL, 26453, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40015000
> close(3) = 0
> open("/lib/libc.so.6", O_RDONLY) = 3
> fstat(3, {st_mode=S_IFREG|0755, st_size=4101324, ...}) = 0
> read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\210\212"..., 4096) = 4096
> old_mmap(NULL, 1001564, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x4001c000
> mprotect(0x40109000, 30812, PROT_NONE) = 0
> old_mmap(0x40109000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0xec000) = 0x40109000
> old_mmap(0x4010d000, 14428, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x4010d000
> close(3) = 0
> mprotect(0x4001c000, 970752, PROT_READ|PROT_WRITE) = 0
> mprotect(0x4001c000, 970752, PROT_READ|PROT_EXEC) = 0
> munmap(0x40015000, 26453) = 0
> personality(PER_LINUX) = 0
> getpid() = 24971
> brk(0) = 0x805230c
> brk(0x805232c) = 0x805232c
> brk(0x8053000) = 0x8053000
> open("/usr/share/locale/locale.alias", O_RDONLY) = 3
> fstat64(0x3, 0xbfffb680) = -1 ENOSYS (Function not implemented)
> fstat(3, {st_mode=S_IFREG|0644, st_size=2265, ...}) = 0
> old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40015000
> read(3, "# Locale name alias data base.\n#"..., 4096) = 2265
> read(3, "", 4096) = 0
> close(3) = 0
> munmap(0x40015000, 4096) = 0
> open("/usr/share/i18n/locale.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
> open("/usr/share/locale/en_US/LC_MESSAGES/net-tools.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
> open("/usr/share/locale/en/LC_MESSAGES/net-tools.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
> ioctl(3, SIOCSARP, 0xbffff874) = 0
> _exit(0) = ?
--
Deepak Saxena - deepak@csociety.purdue.edu - phone://602.790.0500
call me 'evil' call me 'tide is on your side' anything that you want
anybody knows you can conjure anything by the dark of the moon
- Tori Amos, "Suede"