Re: Mirror a file system on the fly

[Dave Schwartz <decebel@gmail.com>]

Ram,

Your code snippet seems to work great as discussed. Thanks. :-)
However, my requirement is slightly different.  What I also want is
that any file created from the mirrored/cloned file-system must not be
available in the parent file system.

Gracias,
decebel


On 8/18/05, Ram Pai <linuxram@us.ibm.com> wrote:
> On Thu, 2005-08-18 at 13:27, Dave Schwartz wrote:
> > Hi Ram,
> > Thanks for the inputs. I was going over the man pages describing the
> > clone system call and its option of CLONE_NEWNS. Could understand the
> > description only in parts.
> >
> > The man page suggests that this flag when set, the cloned child is
> > started in a new name space, initialized with a copy of the parent.
> > Now does that mean, a program like a shell when cloned with
> > CLONE_NEWNS set, will have a copy of file hierarchy of the underlying
> > parent process?
> 
> Yes the child process will see an exact copy of all the mounts of
> various filesystems as that of the parent. However if you mount/unmount
> any filesystems in the child, the same will not be mounted/unmounted in
> the parent and vice-versa.  Each has its individual view of the
> the filesystem heirarchy.
> 
> Try the following program that clones off a child process with a mirror
> namespace and gives you a bash prompt. Try mounting and unmounting
> in this bash prompt and see if the same is visible in a totally
> different window.
> 
> 
> #include  <stdio.h>
> #include  <signal.h>
> #include  <sched.h>
> 
> char somemem[4096];
> 
> int myfunc(){
>         system("bash");
> }
> 
> int
> main(int argc, char *argv[])
> {
>         if(clone(myfunc, somemem, CLONE_NEWNS|SIGCHLD, NULL)) {
>                 wait(NULL);
>         } else {
>                 printf("clone failed\n");
>         }
>         printf("exit\n");
> }
> 
> 
> Hope this helps,
> RP
> 
> 
> 
> 
> >
> > Gracias,
> > decebel
> >
> >
> >
> > On 8/19/05, Ram Pai <linuxram@us.ibm.com> wrote:
> > > On Thu, 2005-08-18 at 12:40, Dave Schwartz wrote:
> > > > Hi list,
> > > >
> > > > Not too sure if this is the right forum to ask this question but since
> > > > my requirement is around linux filesystems, I shall take this liberty
> > > > to post my question.
> > > >
> > > > My requirement is to develop a kernel/user space module to add an
> > > > extension to the shell program environment such that this shell forks
> > > > a mirror look-alike filesystem of the underlying OS to the programs
> > > > run in that particular shell.
> > >
> > > u seem to be talking about namespaces, if I get you right.
> > >
> > > there is a flag CLONE_NEWNS to the system call 'clone' which does what
> > > u r talking about.
> > >
> > > RP
> > >
> > >
> > >
> > >
> > > >
> > > >
> > > > Was trying to look thru the FAQ and a few list archives to look for
> > > > ideas around my requirement. The archives were overwhelming.
> > > >
> > > >
> > > > Any ideas/pointers will be a great help,
> > > > Gracias,
> > > > decebel
> > > > -
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>