From mboxrd@z Thu Jan  1 00:00:00 1970
From: Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 1/2] fs: optimize mpage_readpage()
Date: Sat, 29 May 2010 14:10:19 +0200
Message-ID: <20100529121019.GA25092@liondog.tnic>
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Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
To: Changli Gao <xiaosuo@gmail.com>
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=46rom: Changli Gao <xiaosuo@gmail.com>
Date: Sat, May 29, 2010 at 09:18:46AM +0800

> optimize mpage_readpage()
>=20
> we don't need to initialize bio, and pass it to do_mpage_readpage() a=
s
> parameter, as it is returned by do_mpage_readpage().
>=20
> Signed-off-by: Changli Gao <xiaosuo@gmail.com>
> ----
>  fs/mpage.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> diff --git a/fs/mpage.c b/fs/mpage.c
> index fd56ca2..94ff0d1 100644
> --- a/fs/mpage.c
> +++ b/fs/mpage.c
> @@ -409,14 +409,14 @@ EXPORT_SYMBOL(mpage_readpages);
>   */
>  int mpage_readpage(struct page *page, get_block_t get_block)
>  {
> -	struct bio *bio =3D NULL;
> +	struct bio *bio;
>  	sector_t last_block_in_bio =3D 0;
>  	struct buffer_head map_bh;
>  	unsigned long first_logical_block =3D 0;
> =20
>  	map_bh.b_state =3D 0;
>  	map_bh.b_size =3D 0;
> -	bio =3D do_mpage_readpage(bio, page, 1, &last_block_in_bio,
> +	bio =3D do_mpage_readpage(NULL, page, 1, &last_block_in_bio,
>  			&map_bh, &first_logical_block, get_block);
>  	if (bio)
>  		mpage_bio_submit(READ, bio);

Nope, I don't think that's a good idea.

On the one hand, this is a trick to shut up gcc:

fs/mpage.c: In function =E2=80=98mpage_readpage=E2=80=99:
fs/mpage.c:419: warning: =E2=80=98bio=E2=80=99 is used uninitialized in=
 this function

and, on the other hand, make sure bio is NULL and not some random stack
value since bio is explicitly checked for NULL in do_mpage_readpage().

--=20
Regards/Gruss,
    Boris.