> > The vlan Tag contain three bit for priority. The value 0 indicate no > > priority (on this case the VLAN tag contain only VID). The vlan_tci > > field is set to zero if the frame do not contain the vlan tag. So if > > we have not a vlan tag or no priority in VLAN tag the priority value > > is always 0. > Yes but don't we know that the vlan_tci field is valid? > I don't think you're correct in that 0 means "no priority present", it actually means "best effort" as far as I can tell. Ignoring the VLAN tag when the field is 0 would mean we could use a higher priority from the contents of the frame, which would not be desired? I can add a test with the macro vlan_tx_tag_present() to verify if the vlan_tci field is valid. I test the value 0 to skip the VLAN priority and use the dscp priority in this case. The priority 0 in VLAN tag is often use to turn off the QOS, because not bit is allowed for it. For me is it correct. Nevertheless, if you prefer, I can test only the vlan_tci validity and in this case always use the VLAN priority. > > Sorry but I don't understand. The vlan_tci field it is a __u16 value > > (defined in include/linux/skbuff.h), the VLAN_PRIO_MASK is set to > > 0xE000 and VLAN_PRIO_SHIFT is set to 13 (defined in > > include/linux/if_vlan.h), the vlan_priority is an unsigned char. For > > me the vlan_priority contain a 3-bit value (0xE000 >>13 = 0x0003), why > > 2 ? > Umm? No? Think again about what hweight(0x0003) is. Sorry I made a mistake 0xE000 >>13 = 0x0007 and not 0x0003, and 7 is a 3 bits value. Cedric -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
