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Date: Wed, 22 Nov 2023 22:40:32 -0800
From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: cem@kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 3/9] xfs_copy: actually do directio writes to block
 devices
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References: <170069440815.1865809.15572181471511196657.stgit@frogsfrogsfrogs>
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> diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
> index 79f65946709..26de6b2ee1c 100644
> --- a/copy/xfs_copy.c
> +++ b/copy/xfs_copy.c
> @@ -854,6 +854,8 @@ main(int argc, char **argv)
>  					progname, target[i].name, progname);
>  				exit(1);
>  			}
> +			if (!buffered_output)
> +				open_flags |= O_DIRECT;
>  		}

I'd just move this outside of the if/else if chain and do the
assignment once.

> @@ -887,20 +889,22 @@ main(int argc, char **argv)
>  				}
>  			}
>  		} else  {
> -			char	*lb[XFS_MAX_SECTORSIZE] = { NULL };
> +			char	*lb = memalign(wbuf_align, XFS_MAX_SECTORSIZE);
>  			off64_t	off;
>  
>  			/* ensure device files are sufficiently large */
> +			memset(lb, 0, XFS_MAX_SECTORSIZE);
>  
>  			off = mp->m_sb.sb_dblocks * source_blocksize;
> +			off -= XFS_MAX_SECTORSIZE;
> +			if (pwrite(target[i].fd, lb, XFS_MAX_SECTORSIZE, off) < 0)  {

We should probably check for a short write as well?
Also this line is a bit long.