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Date:   Wed, 26 Feb 2020 08:11:50 -0800
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     Ritesh Harjani <riteshh@linux.ibm.com>
Cc:     jack@suse.cz, tytso@mit.edu, linux-ext4@vger.kernel.org,
        adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org,
        hch@infradead.org, cmaiolino@redhat.com
Subject: Re: [PATCHv3 4/6] ext4: Make ext4_ind_map_blocks work with fiemap
Message-ID: <20200226161150.GA8036@magnolia>
References: <cover.1582702693.git.riteshh@linux.ibm.com>
 <56fc8d3802c578d27d49270600946a0737cef119.1582702694.git.riteshh@linux.ibm.com>
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On Wed, Feb 26, 2020 at 03:27:06PM +0530, Ritesh Harjani wrote:
> For indirect block mapping if the i_block > max supported block in inode
> then ext4_ind_map_blocks may return a -EIO error. But in case of fiemap
> this could be a valid query to ext4_map_blocks.
> So in case if !create then return 0. This also makes ext4_warning to
> ext4_debug in ext4_block_to_path() for the same reason.
> 
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
> ---
>  fs/ext4/indirect.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index 3a4ab70fe9e0..e1ab495dd900 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -102,7 +102,11 @@ static int ext4_block_to_path(struct inode *inode,
>  		offsets[n++] = i_block & (ptrs - 1);
>  		final = ptrs;
>  	} else {
> -		ext4_warning(inode->i_sb, "block %lu > max in inode %lu",
> +		/*
> +		 * It's not yet an error to just query beyond max
> +		 * block in inode. Fiemap callers may do so.
> +		 */
> +		ext4_debug("block %lu > max in inode %lu",
>  			     i_block + direct_blocks +
>  			     indirect_blocks + double_blocks, inode->i_ino);

Does that mean fiemap callers can spamflood dmesg with this message just
by setting the query start range to a huge value?

--D

>  	}
> @@ -537,8 +541,11 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
>  	depth = ext4_block_to_path(inode, map->m_lblk, offsets,
>  				   &blocks_to_boundary);
>  
> -	if (depth == 0)
> +	if (depth == 0) {
> +		if (!(flags & EXT4_GET_BLOCKS_CREATE))
> +			err = 0;
>  		goto out;
> +	}
>  
>  	partial = ext4_get_branch(inode, depth, offsets, chain, &err);
>  
> -- 
> 2.21.0
>