Re: [PATCH v2 1/2] igb_uio: compatible with upstream longterm kernel and RHEL6

[Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>]

2014-11-28 16:13, Jincheng Miao:
> 
> On 11/28/2014 01:01 AM, Thomas Monjalon wrote:
> > 2014-10-31 15:37, Jincheng Miao:
> >> Function pci_num_vf() is introduced from upstream linux-2.6.34. So
> >> this patch make compatible with longterm kernel linux-2.6.32.63.
> >>
> >> For RHEL6's kernel, although it is based on linux-2.6.32, it has
> >> pci_num_vf() implementation. As the same with commit 11ba0426,
> >> pci_num_vf() is defined from RHEL6. So we should check the macro
> >> RHEL_RELEASE_CODE to consider this situation.
> > 
> > Please, could you explain in which case CONFIG_PCI_IOV is defined?
> > The logic is a bit difficult to understand.
> 
> Yep, there is a little confusion for pci_num_vf():
> 1. it is available when CONFIG_PCI_IOV is defined.
> 2. it is introduced from upstream kernel v2.6.34 (fb8a0d9)
> 3. it is implemented from RHEL6.0, although the kernel version is 2.6.32.

Sorry, you didn't described when CONFIG_PCI_IOV is defined.
Is it defined since 2.6.34 upstream? In lower stable versions?
Is it defined since RHEL 6.0?
Why checking CONFIG_PCI_IOV is not sufficient?

When pci_num_vf will be backported in other distributions, we will have to
tune this check and clearly understand what was the situation.

> The logic of this patch is:
> #if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 34) && \
> (!(defined(RHEL_RELEASE_CODE) && RHEL_RELEASE_CODE >= 
> RHEL_RELEASE_VERSION(6, 0) && defined(CONFIG_PCI_IOV)))
> 
> Firstly it detects kernel version, if it is less than 2.6.34, and it is 
> not RHEL-specified, then define pci_num_vf().
> 
> Secondly, it deals with RHEL-specified. If it is RHEL6.0 or later, and 
> CONFIG_PCI_IOV is defined. we should not define pci_num_vf(). If any of 
> these conditions is not reached, pci_num_vf() should be defined.

I can read the check but I don't know why CONFIG_PCI_IOV is checked in the
RHEL case.

> Some days ago, I setup dpdk for longterm kernel 2.6.32.63, and got error:
> ```
> CC [M] 
> /root/dpdk-source/build/build/lib/librte_eal/linuxapp/igb_uio/igb_uio.o
> /root/dpdk-source/build/build/lib/librte_eal/linuxapp/igb_uio/igb_uio.c: 
> In function ‘show_max_vfs’:
> /root/dpdk-source/build/build/lib/librte_eal/linuxapp/igb_uio/igb_uio.c:75: 
> error: implicit declaration of function ‘pci_num_vf’
> ```

Thank you. Describing the problem is helpful for the commit log.
 
> This problem is introduced by commit 11ba04265
> 
> commit 11ba04265cfd2a53c12c030fcaa5dfe7eed39a42
> Author: Guillaume Gaudonville <guillaume.gaudonville-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
> Date: Wed Sep 3 10:18:23 2014 +0200
> 
> igb_uio: fix build on RHEL 6.3
> 
> - pci_num_vf() is already defined in RHEL 6
> - pci_intx_mask_supported is already defined in RHEL 6.3
> - pci_check_and_mask_intx is already defined in RHEL 6.3
> 
> Signed-off-by: Guillaume Gaudonville <guillaume.gaudonville-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
> Signed-off-by: David Marchand <david.marchand-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
> 
> +#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 34) && \
> + !defined(CONFIG_PCI_IOV)
> 
> That is because longterm kernel 2.6.32.63 defined CONFIG_PCI_IOV, but it 
> lacks pci_num_vf(),
> after above processing, pci_num_vf() is still not existed, then build fail.
> 
> My patch could work around it, and can deal with RHEL-specified kernel.

Thanks, we just need to understand the matrix of combinations to be sure
it will be well maintained.

-- 
Thomas