Re: GETHOSTBYNAME()

[Jan Hudec <bulb@ucw.cz>]

On Mon, Mar 24, 2003 at 10:25:11AM +0530, Prasad wrote:
> 
> hi,
> 	i dont think there is one similar to gethostbyname in the 
> kernel-space.  I do think so because most of the work done by 
> gethostbyname is based on the nameservices and is generally not required 
> in the kernel-space.  Implementing it should not be that big a problem.
> once you have the IP of the name server (/etc/resolve.conf???) you can 
> always connect to it and get the IP of the given host.

Implementing it is a big problem, since gethostbyname usualy means a DNS
lookup. Best way to do it in kernel is
call_usermode_helper('/sbin/khost') and call gethostbyname in there.

> On Mon, 24 Mar 2003, shesha bhushan wrote:
> 
> > Hi All
> > I am trying to find the gethostbyname() equivalent function in kernel space. 
> > Does any one know that.
> > The reason is...
> > I am using UDP to transfer data from one machine to another. It is not one 
> > time transfer. Once I get a message from machine A; I need to send some 
> > message back to Machine A from Machine B. For that I was using the following 
> > lines in user space program. I need to do the same in kernel space. Could 
> > any one help me out in this.
> > 
> > struct hostent *data;
> > struct sockaddr_in server;
> > int sock;
> > 
> >   sock = socket(AF_INET, SOCK_DGRAM , 0)
> > 
> > /* binding and all are done here */
> > 
> >   data = gethostbyname("158.168.1.1");

However as long as you are resolving IP address, you should not ask for
gethostbyname. You should ask for inet_aton, which does exist (the name
was mentioned in some list (linux-kernel or this one) not long ago, but
I do not remember it).

> >   memcpy (&server.sin_addrs, data->h_addr, data->h_length);
> >   retval = sendto(sock,msg,sizeof(msg), 0, (struct sockaddr *) &server, 
> > sizeof server);
> > 
> > 
> > Thanking You
> > Shesha
> > 
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-------------------------------------------------------------------------------
						 Jan 'Bulb' Hudec <bulb@ucw.cz>