linux-kernel - Re: [PATCH 3/6] block: open code __generic_file_write

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Date:   Mon, 24 Jul 2023 13:05:57 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Christian Brauner <christian@...uner.io>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] block: open code __generic_file_write_iter for
 blkdev writes

On Thu, Jul 20, 2023 at 04:04:49PM +0200, Christoph Hellwig wrote:
> Open code __generic_file_write_iter to remove the indirect call into
> ->direct_IO and to prepare using the iomap based write code.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  block/fops.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 42 insertions(+), 2 deletions(-)
> 
> diff --git a/block/fops.c b/block/fops.c
> index a286bf3325c5d8..eb599a173ef02d 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -533,6 +533,29 @@ static int blkdev_release(struct inode *inode, struct file *filp)
>  	return 0;
>  }
>  
> +static ssize_t
> +blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	size_t count = iov_iter_count(from);
> +	ssize_t written;
> +
> +	written = kiocb_invalidate_pages(iocb, count);
> +	if (written) {
> +		if (written == -EBUSY)
> +			return 0;
> +		return written;
> +	}
> +
> +	written = blkdev_direct_IO(iocb, from);
> +	if (written > 0) {
> +		kiocb_invalidate_post_direct_write(iocb, count);
> +		iocb->ki_pos += written;
> +	}

I noted in the last series how this could be negative and then crash:

https://lkml.kernel.org/r/ZG6OTWckNlz+P+mo@bombadil.infradead.org

This can be fixed as follows:

diff --git a/block/fops.c b/block/fops.c
index eb599a173ef0..936ed207b5dc 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -536,9 +536,13 @@ static int blkdev_release(struct inode *inode, struct file *filp)
 static ssize_t
 blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
 {
+	struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
 	size_t count = iov_iter_count(from);
 	ssize_t written;
 
+	if (blkdev_dio_unaligned(bdev, iocb->ki_pos, from))
+                return -EINVAL;
+
 	written = kiocb_invalidate_pages(iocb, count);
 	if (written) {
 		if (written == -EBUSY)

With that:

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

  Luis