linux-kernel - Re: [Patch v9 07/10] block: Add fops atomic write support

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Date: Fri, 21 Jun 2024 08:13:34 +0200
From: Hannes Reinecke <hare@...e.de>
To: John Garry <john.g.garry@...cle.com>, axboe@...nel.dk, kbusch@...nel.org,
 hch@....de, sagi@...mberg.me, jejb@...ux.ibm.com,
 martin.petersen@...cle.com, viro@...iv.linux.org.uk, brauner@...nel.org,
 dchinner@...hat.com, jack@...e.cz
Cc: djwong@...nel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
 linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
 linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com, linux-aio@...ck.org,
 linux-btrfs@...r.kernel.org, io-uring@...r.kernel.org, nilay@...ux.ibm.com,
 ritesh.list@...il.com, willy@...radead.org, agk@...hat.com,
 snitzer@...nel.org, mpatocka@...hat.com, dm-devel@...ts.linux.dev
Subject: Re: [Patch v9 07/10] block: Add fops atomic write support

On 6/20/24 14:53, John Garry wrote:
> Support atomic writes by submitting a single BIO with the REQ_ATOMIC set.
> 
> It must be ensured that the atomic write adheres to its rules, like
> naturally aligned offset, so call blkdev_dio_invalid() ->
> blkdev_atomic_write_valid() [with renaming blkdev_dio_unaligned() to
> blkdev_dio_invalid()] for this purpose. The BIO submission path currently
> checks for atomic writes which are too large, so no need to check here.
> 
> In blkdev_direct_IO(), if the nr_pages exceeds BIO_MAX_VECS, then we cannot
> produce a single BIO, so error in this case.
> 
> Finally set FMODE_CAN_ATOMIC_WRITE when the bdev can support atomic writes
> and the associated file flag is for O_DIRECT.
> 
> Reviewed-by: Martin K. Petersen <martin.petersen@...cle.com>
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>   block/fops.c | 20 +++++++++++++++++---
>   1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index 376265935714..be36c9fbd500 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -34,9 +34,12 @@ static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
>   	return opf;
>   }
>   
> -static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
> -			      struct iov_iter *iter)
> +static bool blkdev_dio_invalid(struct block_device *bdev, loff_t pos,
> +				struct iov_iter *iter, bool is_atomic)
>   {
> +	if (is_atomic && !generic_atomic_write_valid(iter, pos))
> +		return true;
> +
>   	return pos & (bdev_logical_block_size(bdev) - 1) ||
>   		!bdev_iter_is_aligned(bdev, iter);
>   }
> @@ -72,6 +75,8 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
>   	bio.bi_iter.bi_sector = pos >> SECTOR_SHIFT;
>   	bio.bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
>   	bio.bi_ioprio = iocb->ki_ioprio;
> +	if (iocb->ki_flags & IOCB_ATOMIC)
> +		bio.bi_opf |= REQ_ATOMIC;
>   
>   	ret = bio_iov_iter_get_pages(&bio, iter);
>   	if (unlikely(ret))
> @@ -343,6 +348,9 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
>   		task_io_account_write(bio->bi_iter.bi_size);
>   	}
>   
> +	if (iocb->ki_flags & IOCB_ATOMIC)
> +		bio->bi_opf |= REQ_ATOMIC;
> +
>   	if (iocb->ki_flags & IOCB_NOWAIT)
>   		bio->bi_opf |= REQ_NOWAIT;
>   
> @@ -359,12 +367,13 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
>   static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>   {
>   	struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
> +	bool is_atomic = iocb->ki_flags & IOCB_ATOMIC;
>   	unsigned int nr_pages;
>   
>   	if (!iov_iter_count(iter))
>   		return 0;
>   
> -	if (blkdev_dio_unaligned(bdev, iocb->ki_pos, iter))
> +	if (blkdev_dio_invalid(bdev, iocb->ki_pos, iter, is_atomic))

Why not passing in iocb->ki_flags here?
Or, indeed, the entire iocb?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich