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Date:   Sun, 7 Apr 2019 09:58:00 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <tom.leiming@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>,
        Jens Axboe <axboe@kernel.dk>,
        linux-block <linux-block@vger.kernel.org>,
        Qu Wenruo <quwenruo.btrfs@gmx.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Omar Sandoval <osandov@fb.com>
Subject: Re: [PATCH] block: don't use for-inside-for in
 bio_for_each_segment_all
Message-ID: <20190407075800.GA9925@lst.de>
References: <20190406215428.3131-1-ming.lei@redhat.com> <20190407065205.GA8799@lst.de> <CACVXFVOZxK7jGUmMH1Q_djE7O=cK1v40O4XQJs4i7TGErJe8Qw@mail.gmail.com> <CACVXFVO9EAFtnspU0H4BNr4UCTry3q6icuHcXDB=c6Ura6BtMw@mail.gmail.com>
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On Sun, Apr 07, 2019 at 03:54:16PM +0800, Ming Lei wrote:
> > OK, will move index check into mp_bvec_advance.
> 
> oops, I recall the above line, because:
> 
> 1) the index check expression is quite straight-forward
> 
> 2) it has been in my todo list to re-use bvec_advance() to re-write
> iterate_bvec()
> given bvec_advance() is much light-weight than for_each_bvec(). If we
> move the index check into bvec_advance(), the helper has to be moved
> to bio.h, then we can't use that for iterate_bvec().

You can always create a tiny wrapper around bvec_advance() that sits
in bio.h.  Which in general is much better style than complex
expressions inside of loops inside of macros..