simulating wireless device (if_alloc panic, VirtualBox, VIMAGE)

Tue Feb 1 19:37:44 UTC 2011

ok here's how it works..

any place you access a V_xxx variable you need to have the current 
vnet set.
so somewhere in your code path to get to that point you have to have done
CURVNET_SET() and after you have finised on the way out you should do
CURVNET_RESTORE().

you can get the vnet from several places:

1/ as shown below, you can get it from any thread's cred if teh 
running thread is part of a
process in the jail in question.
2/ if you have an ifp pointer, you can use ifp->vnet  .   I think 
that's right, it's been a while...
3/ I believe though I may be wrong  (I may be thinking of multi FIBS)
that it maybe in the socket structure too but don't trust me on that 
one.. check it.

if, like in a timer thread you have access to NONE of those, you have 
several choices..
1/ the caller of the timer may have given you indirect access to it in 
the arg.
2/ maybe you juaast have to interate through all the vimages.. to do 
whatever it is that you do
(that happens in some protocols)

On 2/1/11 11:04 AM, Monthadar Al Jaberi wrote:
> On Tue, Feb 1, 2011 at 6:25 PM, Julian Elischer<julian at freebsd.org>  wrote:
>> On 2/1/11 8:40 AM, Monthadar Al Jaberi wrote:
>>> Hi,
>>>
>>> I hope I am on the write place, second try...
>>>
>>> I have written a module that loads fake wifi devices (wtap?) and
>>> distributes packets between them. For now I use route command to route
>>> packets between them from upper layers (TCP,...).
>>> I want to take it to next step and create jails with VNET. I started
>>> reading Julian Elischer's "Vimage: what is it?" and he says that if I
>>> am writing hardware drivers I dont need to make any changes when I
>>> enable VIMAGE option on the kernel, because each one will have their
>>> own stack.
>>>
>>> I can give a more detailed explanation on how my module works. But for
>>> now I get a panic when calling if_alloc() when using option VIMAGE.
>>>
>>> Thank you,
>> while this  was true to some extent it i snot 100% true now.
>> during allocation we now try to have separate interface indexes per vimage
>> which means that the setup routines do need to know the current vnet.
> so I cant call if_alloc directly?
>
>> it looks like wtap_ioctl or wtap_attach should have the following:
>> (copied from the tun driver)
>>
>> this should not be needed from real hardware based drivers as far as I can
>> tell.
>>
>>         CURVNET_SET(CRED_TO_VNET(cred));
>>         /* find any existing device, or allocate new unit number */
>>         i = clone_create(&tunclones,&tun_cdevsw,&u, dev, 0);
>>         [blah]
>>         if_clone_create(name, namelen, NULL);
>>         CURVNET_RESTORE();
> My wtap is based on ath driver code (if_ath.c) which should look like
> a real device right?
> if_ath.c is not using VNET, as far as I can tell....
>
> Currently my module creates a couple of wtaps, which I then create a
> corresponding wlan. These wtaps are interconnected together, so no out
> world yet... so I dont have struct cdev *dev....
>
> Basic idea is my module have a main queue (simulating air) and each
> wtap have a rx_task which sends packets up to higher layers, plus
> callout timer for generation beacons...
>
> I will try to use CURVET_SET(...) tomo
>
>
>>> My setup:
>>> FreeBSD Current 201010 guest on VirtualBox on Ubuntu 10.04.
>>>
>>> Kernel page fault with the following non-sleepable locks held:
>>> exclusive rw ifnet_rw (ifnet_rw) r = 0 (0xc0fc8284) locked @
>>> /usr/src/sys/net/if.c:414
>>> KDB: stack backtrace:
>>> db_trace_self_wrapper(c0cf3cdb,1,0,0,0,...) at db_trace_self_wrapper+0x26
>>> kdb_backtrace(19e,1,ffffffff,c0f9b194,c2fc9a1c,...) at kdb_backtrace+0x2a
>>> _witness_debugger(c0cf6408,c2fc9a30,4,1,0,...) at _witness_debugger+0x25
>>> witness_warn(5,0,c0d2c479,3,c4070d48,...) at witness_warn+0x1fe
>>> trap(c2fc9abc) at trap+0x195
>>> calltrap() at calltrap+0x6
>>> --- trap 0xc, eip = 0xc0970999, esp = 0xc2fc9afc, ebp = 0xc2fc9b1c ---
>>> ifindex_alloc_locked(c0d003cf,c2fc9b36,19e,19e,c15ab714,...) at
>>> ifindex_alloc_locked+0x19
>>> if_alloc(47,c4085a16,3,c0de9614,c32aa780,...) at if_alloc+0x85
>>> wtap_attach(c31a7800,c40857c0,0,4,0,...) at wtap_attach+0x29
>>> new_wtap(c32aa780,0,c2fc9bf0,c083ac9b,c3cbb200,...) at new_wtap+0x9b
>>> wtap_ioctl(c3cbb200,80045701,c31edaa0,1,c3f90b40,...) at wtap_ioctl+0x36
>>> devfs_ioctl_f(c3cfe3b8,80045701,c31edaa0,c3185d00,c3f90b40,...) at
>>> devfs_ioctl_f+0x10b
>>> kern_ioctl(c3f90b40,3,80045701,c31edaa0,fc9cec,...) at kern_ioctl+0x20d
>>> ioctl(c3f90b40,c2fc9cec,c2fc9d28,c0cf5783,0,...) at ioctl+0x134
>>> syscallenter(c3f90b40,c2fc9ce4,c2fc9ce4,0,0,...) at syscallenter+0x263
>>> syscall(c2fc9d28) at syscall+0x34
>>> Xint0x80_syscall() at Xint0x80_syscall+0x21
>>> --- syscall (54, FreeBSD ELF32, ioctl), eip = 0x28181203, esp =
>>> 0xbfbfec3c, ebp = 0xbfbfec58 ---
>>>
>>>
>>> Fatal trap 12: page fault while in kernel mode
>>> cpuid = 0; apic id = 00
>>> fault virtual address   = 0x18
>>> fault code              = supervisor read, page not present
>>> instruction pointer     = 0x20:0xc0970999
>>> stack pointer           = 0x28:0xc2fc9afc
>>> frame pointer           = 0x28:0xc2fc9b1c
>>> code segment            = base 0x0, limit 0xfffff, type 0x1b
>>>                         = DPL 0, pres 1, def32 1, gran 1
>>> processor eflags        = interrupt enabled, resume, IOPL = 0
>>> current process         = 1203 (ioctl)
>>> panic: from debugger
>>> cpuid = 0
>>> Uptime: 21s
>>> Physical memory: 495 MB
>>> Dumping 55 MB: 40 24 8
>>>
>>
>
>