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Date: Mon, 2 Sep 2019 05:20:16 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Gao Xiang <hsiangkao@aol.com>
Subject: Re: [PATCH 13/21] erofs: simplify erofs_grab_bio() since bio_alloc()
 never fail
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Cc: devel@driverdev.osuosl.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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On Sun, Sep 01, 2019 at 01:51:22PM +0800, Gao Xiang wrote:
> From: Gao Xiang <gaoxiang25@huawei.com>
> 
> As Christoph pointed out [1], "erofs_grab_bio tries to
> handle a bio_alloc failure, except that the function will
> not actually fail due the mempool backing it."
> 
> Sorry about useless code, fix it now.

A lot of file systems used to have this, it is a classic that gets
copy and pasted everywhere.  If you feel like doing a little project
it might make sense to check for other places that do the same.

> +		bio = erofs_grab_bio(sb, blkaddr, 1, sb, read_endio);
>  
>  		if (bio_add_page(bio, page, PAGE_SIZE, 0) != PAGE_SIZE) {
>  			err = -EFAULT;
> @@ -275,13 +270,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
>  		if (nblocks > BIO_MAX_PAGES)
>  			nblocks = BIO_MAX_PAGES;
>  
> -		bio = erofs_grab_bio(sb, blknr, nblocks, sb,
> -				     read_endio, false);
> -		if (IS_ERR(bio)) {
> -			err = PTR_ERR(bio);
> -			bio = NULL;
> -			goto err_out;
> -		}
> +		bio = erofs_grab_bio(sb, blknr, nblocks, sb, read_endio);

Btw, I think you should remove erofs_grab_bio in its current form.
The full code in data.c is indeed used in two places, so a local
erofs_raw_page_alloc_bio (or whatever name you prefer) helper here
that hardcodes the sb amd read_endio argument to simplify it a bit
makes sense.

> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index f06a2fad7af2..abe28565d6c0 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1265,7 +1265,7 @@ static bool z_erofs_vle_submit_all(struct super_block *sb,
>  		if (!bio) {
>  			bio = erofs_grab_bio(sb, first_index + i,
>  					     BIO_MAX_PAGES, bi_private,
> -					     z_erofs_vle_read_endio, true);
> +					     z_erofs_vle_read_endio);

But I think here you might as well open code it entirely, or at least
us a separate (and local to zdata.c) helper.