Hi Ophir, Shall I investigate and implement the suggestion from Ferruh to use variable logic?
Thanks Vipin Varghese > -----Original Message----- > From: Yigit, Ferruh > Sent: Monday, April 23, 2018 9:12 PM > To: Varghese, Vipin <vipin.vargh...@intel.com>; Ophir Munk > <ophi...@mellanox.com>; dev@dpdk.org; pascal.ma...@6wind.com; > Thomas Monjalon <tho...@monjalon.net>; Olga Shern > <ol...@mellanox.com>; Shahaf Shuler <shah...@mellanox.com> > Subject: Re: [dpdk-dev] [PATCH 1/2] net/tap: add tun support > > On 4/23/2018 1:58 PM, Varghese, Vipin wrote: > > Hi Ophir, > > > > Can you help me with the investigation with the following information? > > 1) The kernel or distro in which the TAP proto flag set breaks the logic? > > Hi Vipin, > > I guess Ophir's point is not this is broken with some kernels but a valid > field > set wrong for tap, perhaps someone can be using a custom kernel module to > use those fields, we can't know it. > > Instead of duplicating [rt]x_burst() functions, I suggest creating a variable > to > set if this is tun or tap and set pi.proto only for tun, this will lead less > comparison for tap and correct proto value. > > > 2) Is the above still valid even after applying the patch ' > https://dpdk.org/dev/patchwork/patch/37986/'? > > I guess his concern is for tap, that some MAC addresses cause wrong > pi.proto, not for tun which your patch fixes. > > > > > Note: I am testing with 3.13.0, 4.4.0 and 4.13.0. > > > > Thanks > > Vipin Varghese > > > >> -----Original Message----- > >> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Varghese, Vipin > >> Sent: Saturday, April 21, 2018 8:40 PM > >> To: Ophir Munk <ophi...@mellanox.com>; dev@dpdk.org; > >> pascal.ma...@6wind.com; Yigit, Ferruh <ferruh.yi...@intel.com>; > >> Thomas Monjalon <tho...@monjalon.net>; Olga Shern > >> <ol...@mellanox.com>; Shahaf Shuler <shah...@mellanox.com> > >> Subject: Re: [dpdk-dev] [PATCH 1/2] net/tap: add tun support > >> > >> Hi Ophir, > >> > >> <Snip> > >> > >>> Hi Vipin, > >>> I missed your point: > >>> You claim that TAP should work regardless of any pi.proto values. > >>> Can you confirm that for ALL kernels versions (past and future)? > >> > >> I have tested with 3.13.0 , 4.4.0 with patch fix. > >> > >>> > >>>> -----Original Message----- > >>>> From: Ophir Munk > >>>> Sent: Saturday, April 21, 2018 12:49 AM > >>>> To: Varghese, Vipin <vipin.vargh...@intel.com>; dev@dpdk.org; > >>>> pascal.ma...@6wind.com; Yigit, Ferruh <ferruh.yi...@intel.com>; > >>>> Thomas Monjalon <tho...@monjalon.net>; Olga Shern > >>>> <ol...@mellanox.com>; Shahaf Shuler <shah...@mellanox.com> > >>>> Subject: RE: [dpdk-dev] [PATCH 1/2] net/tap: add tun support > >>>> > >>>> Hi Vipin, > >>>> > >>>> Please find comments inline. > >>>> > >>>>> -----Original Message----- > >>>>> From: Varghese, Vipin [mailto:vipin.vargh...@intel.com] > >>>>> Sent: Friday, April 13, 2018 6:18 AM > >>>>> To: Ophir Munk <ophi...@mellanox.com>; dev@dpdk.org; > >>>>> pascal.ma...@6wind.com; Yigit, Ferruh <ferruh.yi...@intel.com>; > >>>>> Thomas Monjalon <tho...@monjalon.net>; Olga Shern > >>>>> <ol...@mellanox.com>; Shahaf Shuler <shah...@mellanox.com> > >>>>> Subject: RE: [dpdk-dev] [PATCH 1/2] net/tap: add tun support > >>>>> > >> > >> <Snip> > >> > >>>>>> 1. Accessing the first byte here assumes it is the first IP > >>>>>> header byte (layer 3) which is correct for TUN. > >>>>>> For TAP however the first byte belongs to Ethernet destination > >>>>>> address (layer 2). > >>>>>> Please explain how this logic will work for TAP. > >>>>> > >>>>> Based on linux code base '/driver/net/tap.c' and '/driver/net/tun.c' > >>>>> from 3.13. to 4.16, > >>>>> > >>>>> Please find my observation below > >>>>> 1. File: tun.c, function: tun_get_user, check for 'tun->flags & > >>>>> TUN_TYPE_MASK' is done and if non ip is taken counter 'rx_dropped' > >>>>> is updated. > >>>>> 2. File: tap.c, there are no checks for 'tap->flags' for IFF_NO_PI > >>>>> in rx data path. Counter 'rx_dropped' is updated in > 'tap_handle_frame'. > >>>>> > >>>> > >>>> I understand that in kernel implementation there is no check for > >>>> tap->flags in file tap.c, however I think there is a bug in dpdk > >>>> tap->rte_eth_tap.c > >>> file. > >>>> Please find below an example which demonstrates this claim. > >>>> > >>>>> Please find my reasoning below > >>>>> 1. First approach was to have separate function for tap and tun TX > >>>>> and > >> RX. > >>>>> But this will introduce code duplication, hence reworked the code > >>>>> as > >>>> above. > >>>> > >>>> I agree. Avoiding code duplication is a good approach. > >>>> > >>>>> 2. During my internal testing assigning dummy value for protocol > >>>>> field in TAP packets, did not show a difference in behaviour. May > >>>>> be there are some specific cases this failing. > >>>>> > >>>>> If there difference in behaviour, can please share the same? > >>>>> > >>>> > >>>> Please consider the following example: > >>>> I am running testpmd with a TAP device, --forward-mode=csum. > >>>> I am injecting a TCP packet, which is forwarded back (mac addresses > >>>> swapped) to the sender. > >>>> Using gdb I set a breakpoint at pmd_tx_burst() in file > >>>> rte_eth_tap.c > >>>> > >>>> Looking at the following code inside pmd_tx_burst(): > >>>> > >>>> 527 char *buff_data = rte_pktmbuf_mtod(seg, void *); > >>>> 528 j = (*buff_data & 0xf0); > >>>> 529 pi.proto = (j == 0x40) ? 0x0008 : > >>>> 530 (j == 0x60) ? 0xdd86 : 0x00; > >>>> > >>>> I am printing the first 20 bytes of buff_data in line 527: > >>>> > >>>> (gdb) p/x *(unsigned char *)buff_data@20 > >>>> $3 = {0x0, 0x25, 0x88, 0x10, 0x66, 0x2, 0xf4, 0x52, 0x14, 0x7a, > >>>> 0x59, 0x81, 0x8, 0x0, 0x45, 0x0, 0x4, 0xdf, 0x0, 0x1} > >>>> > >>>> The gdb printout refers to: > >>>> 6 bytes of destination MAC address: 0x0, 0x25, 0x88, 0x10, 0x66, > >>>> 0x2 > >>>> 6 bytes of source MAC address: 0xf4, 0x52, 0x14, 0x7a, 0x59, 0x81 > >>>> 2 bytes of Ethernet type: 0x8, 0x0 - (IPv4) IP header starting with 0x45, > ... > >>>> which is the byte (0x45) that "j" should have looked at > >>>> > >>>> In the case of TAP - buff_data starts with the destination MAC > >>>> address of the sender (0x0, ...). > >>>> The code in line 528 expects that buff_data would start with an IP > >>>> header protocol (e.g. 0x45), but it is not the case for TAP. > >>>> In my case j=0x0 (line 528) which is harmless (as it ends up with > >>>> setting pi.proto=0x00, which is correct for TAP). > >>>> However, if the sender had an Intel NIC - the destination MAC > >>>> address could have started with: > >>>> $3 = {0x40, 0x25, 0xC2, ... > >>>> Or- > >>>> $3 = {0x64, 0xD4, 0xDA, ... > >>>> > >>>> as 4025C2 and 64D4DA are reserved prefixes for Intel Ethernet MAC > >>>> addresses, see: http://www.coffer.com/mac_find/?string=intel > >>>> > >>>> In this case pi.proto could end up with 0x0008 or 0xdd86 instead of > >>>> 0x0 as expected for TAP. > >>>> > >>>> I hope that this example clarifies the bug I am referring to. > >>>> > >> > >> Thanks for sharing detailed example overview. But as you mentioned > >> this will break ' 4025C2' and ' 64D4DA', This will not solve for the > >> correction > patch ' > >> https://dpdk.org/dev/patchwork/patch/37986/'. > >> > >> Only choice left is separate tx_burst for TAP and TUN PMD, as we do > >> not want to check PMD type on each call. > >> > >> Questions: > >> 1) Is this ok to split tx_burst and have redundant code? > >> 2) Does applications transparently send packets coming from Physical > >> NIC to TAP interface? Does not the application Modifies the DEST MAC > >> addr to TAP interface? > >> > >>>>>> > >>>>>> 2. If the first TUN byte contains 0x2X (which is neither IPv4 nor > >>>>>> IPv6) it will end up by setting ip.proto as 0xdd86. > >>>>>> Please explain how this logic will work for non-IP packets in TUN > >>>>> > >>>>> I see your point. You are correct about this. Thanks for pointing > >>>>> out, may I send correction for this as > >>>>> > >>>>> """ > >>>>> - if (j & (0x40 | 0x60)) > >>>>> - pi.proto = (j == 0x40) ? 0x0008 : 0xdd86; > >>>>> + pi.proto = (j == 0x40) ? 0x0008 : > >>>>> + (j == 0x60) ? 0xdd86 : > >>>>> + 0x00; > >>>>> """
