Re: [PATCH v3 2/9] ext4: skip tail block zeroing for inline data files

[Jan Kara]

On Wed 08-07-26 14:20:42, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> ext4_block_zero_eof() is called from ext4_write_checks() on every
> append write beyond EOF. For inline data files, ext4_get_block()
> returns -ERANGE when ext4_load_tail_bh() looks up the tail block.
> However, this error is currently ignored because the return value
> of ext4_get_block() in ext4_load_tail_bh() is discarded.
> 
> Before we fix ext4_load_tail_bh() to properly propagate the error,
> skip the zeroing for inline data inodes to avoid unnecessary
> failures or confusion.
> 
> Fixes: 3f60efd65412d ("ext4: zero post-EOF partial block before appending write")
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

Hum, but this check is racy (inline data can be removed from
ext4_page_mkwrite() after this check) so we could in theory miss some
zeroing we should do. I didn't put too deep thought to whether it really
can do some harm or not but it would at least deserve a comment.

								Honza

> ---
>  fs/ext4/inode.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 7b2face041ef..a3f7c71b701d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4218,6 +4218,9 @@ int ext4_block_zero_eof(struct inode *inode, loff_t from, loff_t end)
>  	offset = from & (blocksize - 1);
>  	if (!offset || from >= end)
>  		return 0;
> +	/* Inline data has no tail block to zero. */
> +	if (ext4_has_inline_data(inode))
> +		return 0;
>  	/* If we are processing an encrypted inode during orphan list handling */
>  	if (IS_ENCRYPTED(inode) && !fscrypt_has_encryption_key(inode))
>  		return 0;
> -- 
> 2.52.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR