Hi!
While I was making some tests with the socket functions, I intentionally
called socket() this way:
socket(9999, SOCK_STREAM, 0)
(with a protocol family not supported). I was expecting to get a
EPFNOSUPPORT, but I got a EINVAL error code, instead.
After posting a message to comp.protocol.tcp-ip, someone noted that the
socket.h header of his Solaris system had a PF_MAX constant, and that it'd
be possible that a EINVAL was returned for any protocol family number
greater than PF_MAX. I checked my Linux header files, and found in
bits/socket.h the following constants definitions:
#define PF_UNSPEC 0 /* Unspecified. */
#define PF_LOCAL 1 /* Local to host (pipes and file-domain). */
#define PF_UNIX PF_LOCAL /* Old BSD name for PF_LOCAL. */
[....]
#define PF_SNA 22 /* Linux SNA Project */
#define PF_IRDA 23 /* IRDA sockets. */
#define PF_MAX 32 /* For now.. */
and I got surprised that the PF_MAX constant was *not* defined to be 23
(ie., the highest defined protocol number). Why is PF_MAX defined like this?
I changed my socket() call to:
socket(25, SOCK_STREAM, 0)
(with a protocol familiy lower than PF_MAX) suspecting that perhaps now I'd
get a EPFNOSUPPORT. But I still got a EINVAL error code.
So that I had a look at the socket.c source code, and found the following:
int sock_create(int family, int type, int protocol, struct socket **res)
{
int i;
struct socket *sock;
/*
* Check protocol is in range
*/
if(family<0||family>=NPROTO)
return -EINVAL;
#if defined(CONFIG_KMOD) && defined(CONFIG_NET)
/* Attempt to load a protocol module if the find failed.
*
* 12/09/1996 Marcin: But! this makes REALLY only sense, if the user
* requested real, full-featured networking support upon configuration.
* Otherwise module support will break!
*/
if (net_families[family]==NULL)
{
char module_name[30];
sprintf(module_name,"net-pf-%d",family);
request_module(module_name);
}
#endif
if (net_families[family]==NULL)
return -EINVAL;
I don't understand why the code says:
if(family<0||family>=NPROTO)
return -EINVAL;
instead of:
if(family<0||family>=PF_MAX)
return -EPFNOSUPPORT;
(Note that I check "family" against PF_MAX (instead of NPROTO), and that
the return value is EPFNOSUPPORT (instead of EINVAL))
I mean:
Why does the code use NPROTO instead of PF_MAX?
What's the point of having PF_MAX (or NPROTO) defined to be a value greater
than the highest defined protocol number?
If the TCP/IP stack does not return a EPFNOSUPPORT errror code in this case
(the call to socket I pointed out at the beginning of this message), when
would it do it?
Greetings, Fernando (fernando@gont.com.ar)
"I believe it is a Human impossibility to obtain complete peace of mind
in this dimension. There's too much suffering and pain -- particularly
for children." -Dolores O'Riordan
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