From owner-freebsd-hackers  Tue May 30 13:21:14 2000
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From: "Yevmenkin, Maksim N, CSCIO" <myevmenkin@att.com>
To: "'Zhihui Zhang'" <zzhang@cs.binghamton.edu>
Cc: "'freebsd-hackers@freebsd.org'" <freebsd-hackers@FreeBSD.ORG>,
	"'freebsd-current@freebsd.org'" <freebsd-current@FreeBSD.ORG>
Subject: RE: stupid FS questions
Date: Tue, 30 May 2000 16:20:53 -0400
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i know that :) i guess my questions were

1) why the same piece of code duplicated in all ``mount_xxx'' utilities?

2) if we are loading fs kernel module from ``mount_xxx'' why
we have to do it again in kernel? 
if i'm not missing anything, by the time we reach ``mount''
function, fs module will be in the memory and this code will 
never be executed.

thanks,
emax

> I believe that it is used to dynamic load filesystem modules. 
> Please read
> the following pages to understand what is a kernel module:
> 
> http://thc.inferno.tusculum.edu/files/thc/bsdkern.html
> 
> > i've been looking at ``mount_xxx'' code and have noticed 
> "strange" thing.
> > all ``mount_xxx'' utilities have common part of code, like
> > 
> >  	error = getvfsbyname("xxx", &vfc);
> > 	if (error && vfsisloadable("xxx")) {
> >                    if (vfsload("xxx"))
> >                            err(EX_OSERR, "vfsload(xxx)");
> >                    endvfsent();    /* flush cache */
> >                    error = getvfsbyname("xxx", &vfc);
> > 	}
> > 	if (error)
> >                    errx(1, "xxx filesystem is not available");
> > 
> >            if (mount(vfc.vfc_name, dir, mntflags, &args) < 0)
> >                    err(1, NULL);
> > 
> > 1) what is the reason for this? why can't move this code to 
> ``mount''?
> > 2) what is the purpose of the following code in
> > ``/sys/kern/vfs_syscalls.c''?
> > 
> > ...
> >   for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next)
> >                 if (!strcmp(vfsp->vfc_name, fstypename))
> >                         break;
> >         if (vfsp == NULL) {
> >                 linker_file_t lf;
> > 
> >                 /* Refuse to load modules if securelevel raised */
> >                 if (securelevel > 0) {
> >                         vput(vp);
> >                         return EPERM; 
> >                 }
> >                 /* Only load modules for root (very important!) */
> >                 if ((error = suser(p)) != 0) {
> >                         vput(vp);
> >                         return error;
> >                 }
> >                 error = linker_load_file(fstypename, &lf);
> >                 if (error || lf == NULL) {
> >                         vput(vp);
> >                         if (lf == NULL)
> >                                 error = ENODEV;
> >                         return error;
> >                 }
> > ...
> > 
> > from my understanding this is done to load FS module.
> > or did i miss someting?


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