Hi everyone I am trying to understand if its possible to add functions dynamically to the kernel source based on the presence of certain modules in the running kernel image. I did try what brian suggested with the function pointer and yeah it does work. But I could not understand what peter was trying to say about modular users since I suppose he mentioned one module (B in this case) using a function pointer defined in (or by) module A. In my case, since it is the kernel that is gonna use the function, I need to make sure that the module doesn't get unloaded while we are using the function. By the way Jan I couldnt find bridge.c although there is an object file called bridge.o within /net/bridge. Nonetheless, I did check nf_nat_ftp.c as an example to see if something similar is being done there too. What I did find out is that nf_nat_ftp_hook is rcu assigned in nf_nat_ftp.c however this function pointer is being used with nf_contrack_ftp.c (im talkin 2.6.27.45 here). In this case, it still is module1 <- module2 and not kernel <- module. Could you please elaborate a little how it affects the latter case. Or perhaps u were commenting on the former case since peter brought that to our notice. thanks again for your replies and keen to hear your input Regards, Aijaz Baig > > > ---------- Forwarded message ---------- > From: Brian Gerst <brgerst@xxxxxxxxx> > Date: Tue, Aug 24, 2010 at 4:46 PM > Subject: Re: help needed with EXPORT_SYMBOL > To: aijazbaig1@xxxxxxxxx > > > > On Tue, Aug 24, 2010 at 12:44 AM, Aijaz Baig <aijazbaig1@xxxxxxxxx> > wrote: > > Hello everyone, > > > > thanks for sending in the replies with so many options. I am still a > > relative newbie so please do bear with me guys if I sound a bit > naive at > > times. > > > > I'll first start with brian's suggestion. He said: > > "Use an exported function pointer in the main kernel as a hook that > the > > module sets when it is loaded. Note, you must use module_get and > > module_put around the call to the module to prevent it from > unloading > > while in use." > > > > I have never used such a technique and do not understand what you > mean. > > Could you please elaborate a little. Do you mean I should NF_HOOK > within > > the kernel code and then make the function that I would like to > execute > > as the hookfn? Well..if this is what u meant then wouldn't it also > cause > > all hooks at that particular position to be executed as well? > > > > And then peter and finally jan came up with, perhaps better > suggestions > > (i really cannot judge the quality of any of these suggestions..m > too > > much of a noob to do that). I got confused in the XY explanation by > jan > > since there both X and Y are modules it seems and I was talking > about a > > module exporting a certain symbol to be used by the kernel. Peter > did > > suggest notification chains. Is there a simple example that I can > look > > at? Will it allow the kernel to see symbols defined within the > module? > > > > Lastly, will I be able to use kallsyms_lookup() to do what I can? I > > notice that it replaced EXPORT_SYMTAB sometime back. So if yes I can > use > > it, does anyone know how to fill in the very first parameter of this > > function which says address (of what exactly and how am I supposed > to > > know this address?) > > > > Keen to hear from you and once again, thank you for your inputs, > > > You still haven't explained why you want to lookup a symbol in a > module from the main kernel. There is probably a better way of doing > it. > > -- > Brian Gerst > > -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
