Re: Fwd: netdevice.7 SIOCGIFFLAGS/SIOCSIFFLAGS

Hi Alejandro,

we added IFF_ECHO these days on suggestion of Dave Miller - and the 
IFF_LOWER_UP/IFF_DORMANT were already there at that time.

I don't know if there ioctls are still used for retrieving these flags 
as I assume this is done via netlink interface today.

At least there is enough space (in the union) in the ioctl structure for 
longer data structures:

https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/if.h#L265

https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/if.h#L247

https://elixir.bootlin.com/linux/latest/source/net/core/dev_ioctl.c#L114

If you continue discussing about this topic, please remove the 
Volkswagen mail addresses from Urs and me.

I'm still maintaining the CAN subsystem in the Linux kernel - but with a 
private mail address.

And you should better add the netdev ML to your recipients 
netdev@vger.kernel.org where all the netdev guys (including Dave Miller) 
hang out.

Best,
Oliver

------------------------------------------------------------------------
*Von:* Alejandro Colomar (man-pages) [off-list ref]
*Gesendet:* Freitag, März 19, 2021 9:00 PM
*An:* Erik Flodin; mtk.manpages@gmail.com
*Cc:* linux-man@vger.kernel.org; Stefan Rompf; David S. Miller; Fredrik 
Arnerup; John Dykstra; David S. Miller; Hartkopp, Oliver, Dr. (EESC/3); 
Thuermann, Urs, Dr. (K-AERD/M)
*Betreff:* Re: netdevice.7 SIOCGIFFLAGS/SIOCSIFFLAGS
[CC += Fredrik, John, David S., Steven, Oliver, Urs]

Hi,

On 3/17/21 3:12 PM, Erik Flodin wrote:

quoted

Hi,

The documentation for SIOCGIFFLAGS/SIOCSIFFLAGS in netdevice.7 lists
IFF_LOWER_UP, IFF_DORMANT and IFF_ECHO, but those can't be set in
ifr_flags as it is only a short and the flags start at 1<<16.

See also https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=746e6ad23cd6fec2edce056e014a0eabeffa838c 

<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=746e6ad23cd6fec2edce056e014a0eabeffa838c>

quoted

I don't know what's the history of that.
I researched a bit, and while the struct member is indeed a 'short' [1],
the flags were added to the kernel for some reason.
I added a few people to the thread that may know better what to do.Let's
see if they can comment.

Links to relevant commits:

<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=746e6ad23cd6fec2edce056e014a0eabeffa838c 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=746e6ad23cd6fec2edce056e014a0eabeffa838c>>
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b00055aacdb172c05067612278ba27265fcd05ce 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b00055aacdb172c05067612278ba27265fcd05ce>>
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cd05acfe65ed2cf2db683fa9a6adb8d35635263b 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cd05acfe65ed2cf2db683fa9a6adb8d35635263b>>
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=6ecda4d14604d250d385346f4fe9de707f281759 
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=6ecda4d14604d250d385346f4fe9de707f281759>>

Thanks,

Alex

[1]:

.../linux$ sed -n '/struct ifreq {/,/};/p' include/uapi/linux/if.h
struct ifreq {
#define IFHWADDRLEN     6
         union
         {
                 char    ifrn_name[IFNAMSIZ];            /* if name, 
e.g. "en0" */
         } ifr_ifrn;

         union {
                 struct  sockaddr ifru_addr;
                 struct  sockaddr ifru_dstaddr;
                 struct  sockaddr ifru_broadaddr;
                 struct  sockaddr ifru_netmask;
                 struct  sockaddr ifru_hwaddr;
                 short   ifru_flags;
                 int     ifru_ivalue;
                 int     ifru_mtu;
                 struct  ifmap ifru_map;
                 char    ifru_slave[IFNAMSIZ];   /* Just fits the size */
                 char    ifru_newname[IFNAMSIZ];
                 void __user *   ifru_data;
                 struct  if_settings ifru_settings;
         } ifr_ifru;
};
.../linux$ grep 'define\sifr_flags' include/uapi/linux/if.h
#define ifr_flags       ifr_ifru.ifru_flags     /* flags                */
.../linux$

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ 
<https://www.kernel.org/doc/man-pages/>
http://www.alejandro-colomar.es/ <http://www.alejandro-colomar.es/>