Re: [PATCH] ext2: preserve completed DIO bytes when buffered fallback fails

[Jan Kara]

On Mon 02-11-26 06:15:55, Hungyu Lin wrote:
> ext2_dio_write_iter() can complete part of a direct write before
> falling back to buffered I/O for a hole inside i_size. If
> generic_perform_write() then fails, its error overwrites the completed
> direct-I/O byte count.
> 
> For example, on a full filesystem, an 8 KiB write to a file with an
> allocated 4 KiB prefix and a 4 KiB hole overwrites the prefix but returns
> ENOSPC and leaves the file position unchanged. GNU dd with oflag=direct
> consequently reports zero bytes written.
> 
> Preserve a positive direct-I/O result and return the buffered error
> when no bytes were direct-written. This restores the fallback policy of
> generic_file_write_iter(), which ext2 used before its iomap conversion.
> 
> Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hungyu Lin <dennylin0707@xxxxxxxxx>

Thanks. Applied to my tree.

								Honza

> ---
>  fs/ext2/file.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 67fe423c3828..8ddc149d4884 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -145,7 +145,8 @@ static ssize_t ext2_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  		pos = iocb->ki_pos;
>  		status = generic_perform_write(iocb, from);
>  		if (unlikely(status < 0)) {
> -			ret = status;
> +			if (!ret)
> +				ret = status;
>  			goto out_unlock;
>  		}
>  
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR