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    SubjectRe: [PATCH 1/2] fs: optimize mpage_readpage()
    From: Changli Gao <xiaosuo@gmail.com>
    Date: Sat, May 29, 2010 at 09:18:46AM +0800

    > optimize mpage_readpage()
    >
    > we don't need to initialize bio, and pass it to do_mpage_readpage() as
    > parameter, as it is returned by do_mpage_readpage().
    >
    > 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 = NULL;
    > + struct bio *bio;
    > sector_t last_block_in_bio = 0;
    > struct buffer_head map_bh;
    > unsigned long first_logical_block = 0;
    >
    > map_bh.b_state = 0;
    > map_bh.b_size = 0;
    > - bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
    > + bio = 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 ‘mpage_readpage’:
    fs/mpage.c:419: warning: ‘bio’ 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().

    --
    Regards/Gruss,
    Boris.
    --
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