Re: Module : Pipefs : doubts

[Randy.Dunlap]

selvakumar nagendran wrote:
> Hello Randy,
>      Thanks for ur help. See I do know that pipe.o is
> compiled into the main kernel image. But the following
> code block in pipe.c, made me to think as if pipefs
> has been implemented as a module in the kernel. Bcoz
> it used module_init and module_exit macros. That's why
> I got confused. Can u explain the reason for this?

Here's what I suggest.  Look at the kernel header files,
in particular: include/linux/init.h .

Find /module_init/ in that header file.
It has different #defines depending on whether the
including file (e.g., pipe.c) is being
built as a module or not (#ifdef MODULE).

Once you have found that module_init() means __initcall(),
then you can find that __initcall() means device_initcall(),
which in turns means define_initcall("6",fn);
which is a (normal, common) method of setting up a
"module" (functional module, not only for separate
loadable modules) initialization entry point.
There, darn, I've said too much and my rubout key
doesn't work.



> ------------------
> static DECLARE_FSTYPE(pipe_fs_type, "pipefs",
> pipefs_read_super, FS_NOMOUNT);
>
> static int __init init_pipe_fs(void)
> {
> 	int err = register_filesystem(&pipe_fs_type);
> 	if (!err) {
> 		pipe_mnt = kern_mount(&pipe_fs_type);
> 		err = PTR_ERR(pipe_mnt);
> 		if (IS_ERR(pipe_mnt))
> 			unregister_filesystem(&pipe_fs_type);
> 		else
> 			err = 0;
> 	}
> 	return err;
> }
>
> static void __exit exit_pipe_fs(void)
> {
> 	unregister_filesystem(&pipe_fs_type);
> 	mntput(pipe_mnt);
> }
>
> module_init(init_pipe_fs)
> module_exit(exit_pipe_fs)
>
>
> --- "Randy.Dunlap" <rddunlap@xxxxxxxx> wrote:
>
> > selvakumar nagendran wrote:
> >
> > > Hello linux-experts,
> > >    I went through the kernel source code file
> > > /fs/pipe.c and I found that the pipe file system
> > > configured as a module. But in lsmod I am unable
> >
> > to
> >
> > > see it. This is my first doubt.
>
>  
>  Where do you see that?
>  fs/pipe.o is always built into the kernel image.


--
~Randy
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