Re: [Nbd] [RFC]Some questions about NBD

[Goswin von Brederlow <goswin-v-b@...186...>]

harryxiyou <harryxiyou@...17...> writes:

> Hi Wouter,
>
> I have some questions to ask you, which are like following.
>
> 1, Pavel said "Unlike NFS, it is possible to put any file system on it. But
>    (also unlike NFS), if someone has mounted NBD read/write, you must
>    assure that no one else will have it mounted. " on his own page. The
>    URL is http://atrey.karlin.mff.cuni.cz/~pavel/nbd/nbd.html . But i can not
>    understand '' if someone has mounted NBD read/write, you must
>    assure that no one else will have it mounted.". What is exact meaning of
>    this sentence.
>            One of my thoughts looks like this. We have two users, a1
> and a2 , who
>    have logined into a Linux OS. If a1 mounted NBD read/write, a2 must not
>    mount it currently, right?

More like Host1 and Host2. Although there are several filesystems out
there that specifically are designed for multiple hosts to mount it
(gfs, ocfs, ...).

> 2, I have seen the main function of nbd-server.c, which version is nbd-2.9.15.
>    Some stuffs confuse me like following.
>        1> 1882 line: memset(pidftemplate, '\0', 256);
>             I just see pidftemplate is used in the daemon function.
> But i am not
>        sure what the pid file is used for. And also i don't know the meaning of
>        this daemon function in nbd-server.c.
>
>        2> 1873: SERVER *server;
>             If we have (server != NULL && (0 == server->port)) we will
> execute inetd
>        mode. I have searched the characters of inetd but i am not sure what the
>        meanings of inetd in our nbd-server.c do. And in what
> situations, we will do
>        the inetd mode, which should do what jobs?

You can have nbd-server running as standalone server or have inetd start
it on demand.

>        3> 1928: dousers();
>             I just tracked this function. It looks like it will set
> the running group and
>        user informations. Why should we do this? Is it related to what
> pavel said
>        "if someone has mounted NBD read/write, you must assure that no one else
>         will have it mounted". Right ?
>
> This time, i just ask these questions. If i have other ones, i will
> send to you ;D
> Thanks very much, Wouter.
>
> -- 
> Thanks
> Harry Wei

MfG
        Goswin