Re: [PATCH] net/tap: fix build issue with ARM32

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

-----Original Message-----
> Date: Wed, 31 Jan 2018 11:57:10 +0000
> From: Ophir Munk <ophirmu@mellanox.com>
> To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> CC: "dev@dpdk.org" <dev@dpdk.org>, Thomas Monjalon <thomas@monjalon.net>,
>  Pascal Mazon <pascal.mazon@6wind.com>, Jan Viktorin
>  <viktorin@rehivetech.com>, Jianbo Liu <jianbo.liu@arm.com>
> Subject: RE: [dpdk-dev]  [PATCH] net/tap: fix build issue with ARM32
> 
> 
> 
> > -----Original Message-----
> > From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> > Sent: Wednesday, January 31, 2018 1:31 PM
> > To: Ophir Munk <ophirmu@mellanox.com>
> > Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; Pascal
> > Mazon <pascal.mazon@6wind.com>; Jan Viktorin
> > <viktorin@rehivetech.com>; Jianbo Liu <jianbo.liu@arm.com>
> > Subject: Re: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> > 
> > -----Original Message-----
> > > Date: Wed, 31 Jan 2018 10:38:32 +0000
> > > From: Ophir Munk <ophirmu@mellanox.com>
> > > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > > CC: "dev@dpdk.org" <dev@dpdk.org>, Thomas Monjalon
> > > <thomas@monjalon.net>,  Pascal Mazon <pascal.mazon@6wind.com>,
> > Jan
> > > Viktorin  <viktorin@rehivetech.com>, Jianbo Liu <jianbo.liu@arm.com>
> > > Subject: RE: [dpdk-dev]  [PATCH] net/tap: fix build issue with ARM32
> > >
> > > Hi,
> > > Please see inline
> > >
> > > > -----Original Message-----
> > > > From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> > > > Sent: Wednesday, January 31, 2018 12:24 PM
> > > > To: Ophir Munk <ophirmu@mellanox.com>
> > > > Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; Pascal
> > > > Mazon <pascal.mazon@6wind.com>; Jan Viktorin
> > > > <viktorin@rehivetech.com>; Jianbo Liu <jianbo.liu@arm.com>
> > > > Subject: Re: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> > > >
> > > > -----Original Message-----
> > > > > Date: Wed, 31 Jan 2018 09:59:45 +0000
> > > > > From: Ophir Munk <ophirmu@mellanox.com>
> > > > > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>, "dev@dpdk.org"
> > > > >  <dev@dpdk.org>
> > > > > CC: Thomas Monjalon <thomas@monjalon.net>, Pascal Mazon
> > > > > <pascal.mazon@6wind.com>, Jan Viktorin <viktorin@rehivetech.com>,
> > > > > Jianbo  Liu <jianbo.liu@arm.com>
> > > > > Subject: RE: [dpdk-dev]  [PATCH] net/tap: fix build issue with
> > > > > ARM32
> > > > >
> > > > > Hi,
> > > > > Please see comments inline
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jerin Jacob
> > > > > > Sent: Wednesday, January 31, 2018 7:14 AM
> > > > > > To: dev@dpdk.org
> > > > > > Cc: Thomas Monjalon <thomas@monjalon.net>; Jerin Jacob
> > > > > > <jerin.jacob@caviumnetworks.com>; Pascal Mazon
> > > > > > <pascal.mazon@6wind.com>; Jan Viktorin
> > > > > > <viktorin@rehivetech.com>; Jianbo Liu <jianbo.liu@arm.com>
> > > > > > Subject: [dpdk-dev] [PATCH] net/tap: fix build issue with ARM32
> > > > > >
> > > > > > arm32 Linux does not support eBPF interface.
> > > > > > Since tap PMD driver has a dependency on eBPF(the symbol
> > > > > > __NR_bpf), disabling it armv7 config.
> > > > > >
> > > > > > compilation error log:
> > > > > > In file included from /tmp/dpdk/drivers/net/tap/tap_bpf_api.c:15:0:
> > > > > > /tmp/dpdk/drivers/net/tap/tap_bpf.h:103:4: error: #error
> > > > > > __NR_bpf not defined  #  error __NR_bpf not defined
> > > > > >     ^
> > > > >
> > > > > arm architecture is missing is file drivers/tap/tap_bpf.h I
> > > > > suggest adding it, for example
> > > > >
> > > > > # elif defined(__arm__)
> > > > > #  define __NR_bpf 386
> > > >
> > > > By looking at Linux source code
> > > >
> > https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fel
> > > > ixi
> > > > r.free-
> > > >
> > electrons.com%2Flinux%2Fv4.15%2Fsource%2Ftools%2Fbuild%2Ffeature%2
> > > > Ftest-
> > > >
> > bpf.c%23L6&data=02%7C01%7Cophirmu%40mellanox.com%7C19f50ad7f27
> > > >
> > 34d00173808d56894c997%7Ca652971c7d2e4d9ba6a4d149256f461b%7C0%
> > > >
> > 7C0%7C636529910613736017&sdata=ynsxHG9fvao4LyfWLo4GVJjlKNmcF0q
> > > > 0BkFocJyarAE%3D&reserved=0
> > > > I am not sure, Is eBPF support available for arm32 support?
> > >
> > > TAP eBPF has a graceful approach: it must successfully compile on all
> > > Linux distributions. If a specific kernel cannot support eBPF it will
> > > gracefully refuse the eBPF netlink message sent to it.
> > > Thus, there is no harm even if there is no eBPF support available for arm32.
> > 
> > OK. But, To enable grace full refuse, we should not any random system call
> > number like #define __NR_bpf 386.
> > It should at least unused for arm32.
> > 
> 
> For arm - system call 386 seems to be used only for eBPF
> http://elixir.free-electrons.com/linux/v4.15/source/arch/arm64/include/asm/unistd32.h#L796
> 
> 
> > >
> > > You should enable TAP compilation for cases where you only need TAP
> > without eBPF.
> > 
> > Yes. It would have been better if new eBPF depended features would have
> > under conditional compilation flag so it it can be turned off selectively.
> > 
> 
> I am in favor of keeping configuration as simple as possible if possible.
> I will issue a PR which includes arm BPF definition

OK.

Looks like systemd is using the similar method.
https://github.com/systemd/systemd/blob/master/src/basic/missing_syscall.h#L334