Re: [PATCH] ax25.h unsigned long type for ax25 timers

[Bernard Pidoux F6BVP <f6bvp@xxxxxxx>]

There have been in the past already some modifications of 
ax25_info_struct and the old one was renamed deprecated.

/* this will go away. Please do not export to user land */
struct ax25_info_struct_deprecated {
        unsigned int    n2, n2count;
        unsigned int    t1, t1timer;
        unsigned int    t2, t2timer;
        unsigned int    t3, t3timer;
        unsigned int    idle, idletimer;
        unsigned int    state;
        unsigned int    rcv_q, snd_q;
};

Three new items were included :

...
        unsigned int    vs, vr, va, vs_max;
        unsigned int    paclen;
        unsigned int    window;
};

At the same time  case SIOCAX25GETINFOOLD:
was added in ax25_ioctl()
and would trigger a warning message.


 /* old structure? */
                if (cmd == SIOCAX25GETINFOOLD) {
                        static int warned = 0;
                        if (!warned) {
                                printk(KERN_INFO "%s uses old 
SIOCAX25GETINFO\n",
                                        current->comm);
                                warned=1;
                        }

                        if (copy_to_user(argp, &ax25_info, 
sizeof(struct ax25_info_struct_deprecated))) {
                                res = -EFAULT;
                                break;
                        }
                } else {
                        if (copy_to_user(argp, &ax25_info, 
sizeof(struct ax25_info_struct))) {
                                res = -EINVAL;
                                break;
                        }
                }
                res = 0;
                break;

Here is my question :

Can't we remove the probably quite old ax25_info_struct_deprecated 
structure, and rename the present ax25_info_struct, 
ax25_info_struct_deprecated, then create the new ax25_info_struct with 
resized timers unsigned long ?

The second solution is to declare a new structure

* new ax25 info struct */
struct ax25_info_long_timers_struct {
        unsigned int    n2, n2count;
        unsigned long   t1, t1timer;
        unsigned long   t2, t2timer;
        unsigned long   t3, t3timer;
        unsigned long   idle, idletimer;
        unsigned int    state;
        unsigned int    rcv_q, snd_q;
        unsigned int    vs, vr, va, vs_max;
        unsigned int    paclen;
        unsigned int    window;
};

adding another case SIOCAX25GETNEWINFO
that would be defined
#define SIOCAX25GETNEWINFO         (SIOCPROTOPRIVATE+14)

and trigger warning message by calls to SIOCAX25GETINFOOLD and
SIOCAX25GETINFO.

It that the right way to do it ?


Bernard, f6bvp



Bernard Pidoux wrote:
> David,
>
> Your explanation is perfectly clear and I understand the problem now.
> Thank you very much for taking the time to explain me that.
>
> Bernard Pidoux
>
>
>
>
> David Miller wrote:
> > From: Bernard Pidoux <bpidoux@xxxxxxx>
> > Date: Thu, 19 Jun 2008 18:28:46 +0200
> >
> > > Unfortunately I don't quite understand exactly why a structure in 
> > > user space cannot be changed.
> >
> > Because there are userland binaries already compiled out there using
> > the current structure layout.  If we change the kernel, those binaries
> > stop using a datastructure that matches what the kernel is using.
> > Such binaries will break.
> >
> > In generic, because of this, you can never change the layout of a
> > data structure exported to userland as a kernel interface.
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