Date: Fri, 23 Apr 2010 08:10:44 +0200 (CEST) From: "=?ISO-8859-15?Q?Luk=E1=A8_Czerner?=" <czerner.lukas@gmail.com> To: Gleb Kurtsou <gleb.kurtsou@gmail.com> Cc: freebsd-hackers@freebsd.org, =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= <czerner.lukas@gmail.com> Subject: Re: How to change vnode operations ? Message-ID: <alpine.DEB.1.10.1004230756190.7101@a04-0215a.kn.vutbr.cz> In-Reply-To: <20100422191849.GA9895@tops> References: <alpine.DEB.1.10.1004221559270.7101@a04-0215a.kn.vutbr.cz> <20100422191849.GA9895@tops>
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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-123159715-1272003045=:7101 Content-Type: TEXT/PLAIN; charset=utf-8 Content-Transfer-Encoding: 8BIT On Thu, 22 Apr 2010, Gleb Kurtsou wrote: > Date: Thu, 22 Apr 2010 22:18:49 +0300 > From: Gleb Kurtsou <gleb.kurtsou@gmail.com> > To: Lukáš Czerner <czerner.lukas@gmail.com> > Cc: freebsd-hackers@freebsd.org > Subject: Re: How to change vnode operations ? > > On (22/04/2010 16:02), Lukáš Czerner wrote: > > Hi all, > > > > this may sound a little odd, since I have noticed that there is much > > work done to not allow such a thing ($SUBJ). But may be you can help > > me and point me to the right direction. > > > > I am writing a kernel module with somewhat similar functionality > > like nullfs has, BUT it has to have some features which nullfs > > itself does not provide : > > > > 1. I need the new layer to completely hide underlaying layer so no > > one can bypass it. > Is hypothetic 'mount -t mynullfs /a /a' good enough for you? I'm not sure > what your goals are but completely finding underlaying filesystem won't > be easy because of VFS_GET, getfh and other stuff operating with inode > numbers. Well, it may be good enough, or not. Thats what I am trying to find out. Obviously there are problems, as you mentioned, which will not exist when I change the vop_vector of the vnode, but as I thought and you mentioned it as well, this is not very clean way. > > > 2. Nullfs allows me to to overlay just one directory, but i want to > > include another directories and/or exclude subdirectories/files. > > 3. Nullfs just redirects vnode operations to lower layer, I need to > > catch that operation, do something (for example alter the arguments > > somehow etc..), pass the operation (with possibly altered arguments) > > to the lower layer, get the result and then return the result. > I'd suggest to take a look at pefs: http://github.com/glk/pefs > It's cryptographic stacked filesystem for FreeBSD. It changes file > names, hides directory entries, modifies data from lower layer > (encrypts or decrypts), supports mounting on same directory, etc. Thats great, thanks! I will look at it. > > > The best way to do that (I think) is to change vnode operations of > > particular vnodes to point to functions defined in that module. At > > this point, I can catch any operations with the vnode and this is > > the base of what i want. > > > > So my question is. I there any "clean" way to chande vnode > > operations ? If not, is there any "not so clean" way ? Anyway I will > > appreciate any good idea how to do what I have described. > Imho, stacked filesystem is the only right way to do it (see null, > unionfs, pefs). OK. Thanks for pointing me to the pefs, it is interesting and looks like a good start. But I would appreciate more comment on the side of the whole idea about changing vnode operations from the kernel module. It is a little hacky, but aside this I do not see any bigger problems, do you ? Thanks. -Lukas --8323329-123159715-1272003045=:7101--
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