Re: [PATCH] netdevice.7: Update documentation for SIOCGIFADDR SIOCSIFADDR SIOCDIFADDR

["Pali Rohár" <pali@kernel.org>]

Hello!

On Saturday 02 January 2021 19:04:06 Alejandro Colomar (man-pages) wrote:
> Hi Pali,
> 
> Please, see some comments below.
> 
> On 1/2/21 3:02 PM, Pali Rohár wrote:
> > Also add description for struct in6_ifreq which is used for IPv6 addresses.
> > 
> > SIOCSIFADDR and SIOCDIFADDR can be used to add or delete IPv6 address and
> > pppd is using these ioctls for a long time. Surprisingly SIOCDIFADDR cannot
> > be used for deleting IPv4 address but only for IPv6 addresses.
> > 
> > Signed-off-by: Pali Rohár <pali@kernel.org>
> > ---
> >  man7/netdevice.7 | 36 +++++++++++++++++++++++++++++-------
> >  1 file changed, 29 insertions(+), 7 deletions(-)
> > 
> > diff --git a/man7/netdevice.7 b/man7/netdevice.7
> > index 488e83d9a..5b68e4988 100644
> > --- a/man7/netdevice.7
> > +++ b/man7/netdevice.7
> > @@ -55,9 +55,27 @@ struct ifreq {
> >  .EE
> >  .in
> >  .PP
> > +Exception is
> > +.B AF_INET6
> > +socket for which is used
> > +.I in6_ifreq
> > +structure:
> 
> Wording fix:
> 
> [
> AF_INET6 is an exception.
> It passes an
> .I in6_ifreq
> structure:
> ]

Ok, I will fix it.

> Are there more exceptions?
> Or is it the only one?

I really do not know. I played only with the IPv4 and IPv6 sockets.

I come across this incompatibility during reading pppd source code that
it has different structures for IPv4 and IPv6 which are passed to
SIOCSIFADDR ioctl.

> > +.PP
> > +.in +4n
> > +.EX
> > +struct in6_ifreq {
> > +    struct in6_addr     ifr6_addr;
> > +    u32                 ifr6_prefixlen;
> > +    int                 ifr6_ifindex; /* Interface index */
> > +};
> > +.EE
> > +.in
> > +.PP
> >  Normally, the user specifies which device to affect by setting
> >  .I ifr_name
> > -to the name of the interface.
> > +to the name of the interface or
> > +.I ifr6_ifindex
> > +to the index of the interface.
> 
> I've seen there's ifr_ifindex too (see SIOCGIFNAME).
> Can it be used in the same way as ifr6_ifindex?

Sorry, I do not know too. In all applications I saw that they are using
ifr_name for IPv4 stuff.

This needs to be tested if ifr_ifindex instead of ifr_name works for
specifying IPv4 address.

> >  All other members of the structure may
> >  share memory.
> >  .SS Ioctls
> > @@ -142,13 +160,17 @@ IFF_ISATAP:Interface is RFC4214 ISATAP interface.
> >  .PP
> >  Setting the extended (private) interface flags is a privileged operation.
> >  .TP
> > -.BR SIOCGIFADDR ", " SIOCSIFADDR
> > -Get or set the address of the device using
> > -.IR ifr_addr .
> > -Setting the interface address is a privileged operation.
> > -For compatibility, only
> > +.BR SIOCGIFADDR ", " SIOCSIFADDR ", " SIOCDIFADDR
> > +Get, set or delete the address of the device using
> > +.IR ifr_addr " or " ifr6_addr " with " ifr6_prefixlen .
> 
> Generally, we place each name on a single line.
> The line after .TP is an exception, as you can see above.
> So this would be:
> 
> [
> .IR ifr_addr ,
> or
> .I ifr6_addr
> with
> .IR ifr6_prefixlen .
> ]

Ok, I will change it.

> > +Setting or deleting the interface address is a privileged operation.
> > +For compatibility,
> > +.BR SIOCGIFADDR " returns only " AF_INET " addresses, "
> > +.BR SIOCSIFADDR " accepts " AF_INET " and " AF_INET6 " addresses and "
> > +.BR SIOCDIFADDR " deletes only " AF_INET6 " addresses. "
> 
> See above.
> 
> >  .B AF_INET
> > -addresses are accepted or returned.
> > +address can be deleted by setting zero address via
> > +.BR SIOCSIFADDR .
> >  .TP
> >  .BR SIOCGIFDSTADDR ", " SIOCSIFDSTADDR
> >  Get or set the destination address of a point-to-point device using
> > 
> 
> Thanks,
> 
> Alex
> 
> -- 
> Alejandro Colomar
> Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
> http://www.alejandro-colomar.es/