Re: [PATCH, RFC] ext4: add EXT4_IOC_ALLOC_DA_BLKS ioctl

[Eric Sandeen <sandeen@redhat.com>]

Aneesh Kumar K.V wrote:
> On Wed, Mar 11, 2009 at 05:41:05PM -0500, Eric Sandeen wrote:
>> Theodore Ts'o wrote:
>>> Add an ioctl which forces all of the delay allocated blocks to be
>>> allocated.  This also provides a function ext4_alloc_da_blocks() which
>>> will be used by the following commits to force files to be fully
>>> allocated to preserve application-expected ext3 behaviour.
>>>
>> Is it worth checking whether a) the file has delalloc blocks, and/or b)
>> whether the mapping is dirty before we spin off a filemap_flush?
>>
> +int ext4_alloc_da_blocks(struct inode *inode)
> +{
> +       if (!EXT4_I(inode)->i_reserved_data_blocks &&
> +           !EXT4_I(inode)->i_reserved_meta_blocks)
> +               return 0;
> 
> This check test does (a). Since the ioctl is to force allocation of
> delayed allocated blocks i guess (a) is enough because we don't want to
> cause a filemap_flush when we don't have any delayed allocated blocks
> but have dirty pages around.

and b) is as simple as

if (!mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY))
	return 0;

I think?

-Eric