[PATCH v1] net: cdc_ncm: update datagram size after changing mtu

[PATCH v1] net: cdc_ncm: update datagram size after changing mtu

[Robert Dobrowolski]

From: Rafal Redzimski <rafal.f.redzimski@intel.com>

Current implementation updates the mtu size and notify cdc_ncm
device using USB_CDC_SET_MAX_DATAGRAM_SIZE request about datagram
size change instead of changing rx_urb_size.

Whenever mtu is being changed, datagram size should also be
updated.

Cc: <stable@vger.kernel.org>
Signed-off-by: Rafal Redzimski <rafal.f.redzimski@intel.com>
Signed-off-by: Robert Dobrowolski <robert.dobrowolski@linux.intel.com>
---
 drivers/net/usb/cdc_ncm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 2fb31ed..4a47656 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -746,6 +746,8 @@ int cdc_ncm_change_mtu(struct net_device *net, int new_mtu)
 	if (new_mtu <= 0 || new_mtu > maxmtu)
 		return -EINVAL;
 	net->mtu = new_mtu;
+	cdc_ncm_set_dgram_size(dev, new_mtu);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(cdc_ncm_change_mtu);
-- 
1.9.1

Re: [PATCH v1] net: cdc_ncm: update datagram size after changing mtu

[Bjørn Mork]

Robert Dobrowolski <robert.dobrowolski@linux.intel.com> writes:

> From: Rafal Redzimski <rafal.f.redzimski@intel.com>
>
> Current implementation updates the mtu size and notify cdc_ncm
> device using USB_CDC_SET_MAX_DATAGRAM_SIZE request about datagram
> size change instead of changing rx_urb_size.
>
> Whenever mtu is being changed, datagram size should also be
> updated.

Definitely!  Thanks for this.  But looking at the code I believe you
need to fix the calculation of maxmtu too.  It is currently:

  int maxmtu = ctx->max_datagram_size - cdc_ncm_eth_hlen(dev);

And cdc_ncm_set_dgram_size() updates ctx->max_datagram_size with the new
mtu, meaning that you can only reduce the mtu.  We should probably use
cdc_ncm_max_dgram_size() instead here.

And cdc_ncm_set_dgram_size() takes the datagram size with header as
input (ref the above maxmtu calucalution), so it probably needs to
called as

  cdc_ncm_set_dgram_size(dev, new_mtu + cdc_ncm_eth_hlen(dev));

to get it right.  I think.  None of this is tested on an actual device
yet...  Care to test if I'm right, and do a v2 if necessry?

> Cc: <stable@vger.kernel.org>

This should be dropped for net.  Ask David to queue it for stable
instead.  I usually do that by using a subject prefix like

 [PATCH net,stable v1] ...




Bjørn

Re: [PATCH v1] net: cdc_ncm: update datagram size after changing mtu

[Robert Dobrowolski]

> Robert Dobrowolski <robert.dobrowolski@linux.intel.com> writes:
>
>> From: Rafal Redzimski <rafal.f.redzimski@intel.com>
>>
>> Current implementation updates the mtu size and notify cdc_ncm
>> device using USB_CDC_SET_MAX_DATAGRAM_SIZE request about datagram
>> size change instead of changing rx_urb_size.
>>
>> Whenever mtu is being changed, datagram size should also be
>> updated.
>
> Definitely!  Thanks for this.  But looking at the code I believe you
> need to fix the calculation of maxmtu too.  It is currently:
>
>   int maxmtu = ctx->max_datagram_size - cdc_ncm_eth_hlen(dev);
>
> And cdc_ncm_set_dgram_size() updates ctx->max_datagram_size with the new
> mtu, meaning that you can only reduce the mtu.  We should probably use
> cdc_ncm_max_dgram_size() instead here.
>
> And cdc_ncm_set_dgram_size() takes the datagram size with header as
> input (ref the above maxmtu calucalution), so it probably needs to
> called as
>
>   cdc_ncm_set_dgram_size(dev, new_mtu + cdc_ncm_eth_hlen(dev));
>
> to get it right.  I think.  None of this is tested on an actual device
> yet...  Care to test if I'm right, and do a v2 if necessry?
>
>> Cc: <stable@vger.kernel.org>
>
> This should be dropped for net.  Ask David to queue it for stable
> instead.  I usually do that by using a subject prefix like
>
>  [PATCH net,stable v1] ...
>
>
>
>
> Bjørn
>

ok, thanks for feedback I will send v2 patch