Re: [PATCH] fix __swap_writepage() compile failure on old gcc versions

[Chris Mason <clm@fb.com>]

On 06/14/2014 02:12 AM, Al Viro wrote:
> On Fri, Jun 13, 2014 at 03:48:43PM +0100, Al Viro wrote:
>> On Fri, Jun 13, 2014 at 09:03:36PM +0900, Tetsuo Handa wrote:
>>> >From 75b9f78ddc8ab30555a520f5a2477a9340341dd1 Mon Sep 17 00:00:00 2001
>>> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Date: Fri, 13 Jun 2014 12:35:35 +0900
>>> Subject: [PATCH pre 3.16-rc1] bio: Fix build failure.
>>>
>>> Commit 62a8067a7f "bio_vec-backed iov_iter" introduced an unnamed union
>>> inside a struct which gcc-4.4.7 cannot handle. Name the unnamed union as
>>> u in order to fix build failure.
>>
>> Sigh...  Oh, well - it will be a while until we can use them (anon union
>> and struct members are valid C11; it's not just gccism).  Applied, will
>> push to Linus today if he hasn't picked that one up himself.
> 
> Let's do this instead: there is only one place in the entire tree that
> steps into this breakage.  Anon structs and unions work in older gcc
> versions; as the matter of fact, we have those in the tree - see e.g.
> struct ieee80211_tx_info in include/net/mac80211.h
> 
> What doesn't work is handling their initializers:

[ ... ]

> ---
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 33bb38c..fe24f78 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -269,8 +269,8 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>  			.count = PAGE_SIZE,
>  			.iov_offset = 0,
>  			.nr_segs = 1,
> -			.bvec = &bv
>  		};
> +		from.bvec = &bv;	/* older gcc versions are broken */

This was how I tested before my last pull request, it was enough to
compile on gcc 4.4.6.

-chris