[PATCH 2/2] ubifs: Allow O_DIRECT

[Dongsheng Yang]

On 08/20/2015 04:35 AM, Richard Weinberger wrote:
> Currently UBIFS does not support direct IO, but some applications
> blindly use the O_DIRECT flag.
> Instead of failing upon open() we can do better and fall back
> to buffered IO.

Hmmmm, to be honest, I am not sure we have to do it as Dave
suggested. I think that's just a work-around for current fstests.

IMHO, perform a buffered IO when user request direct IO without
any warning sounds not a good idea. Maybe adding a warning would
make it better.

I think we need more discussion about AIO&DIO in ubifs, and actually
I have a plan for it. But I have not listed the all cons and pros of
it so far.

Artem, what's your opinion?

Yang
>
> Cc: Dongsheng Yang <yangds.fnst at cn.fujitsu.com>
> Cc: dedekind1 at gmail.com
> Suggested-by: Dave Chinner <david at fromorbit.com>
> Signed-off-by: Richard Weinberger <richard at nod.at>
> ---
>   fs/ubifs/file.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> index a3dfe2a..a61fe86 100644
> --- a/fs/ubifs/file.c
> +++ b/fs/ubifs/file.c
> @@ -1540,6 +1540,15 @@ static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
>   	return 0;
>   }
>
> +/*
> + * For now fall back to buffered IO.
> + */
> +static ssize_t ubifs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
> +				   loff_t offset)
> +{
> +	return 0;
> +}
> +
>   const struct address_space_operations ubifs_file_address_operations = {
>   	.readpage       = ubifs_readpage,
>   	.writepage      = ubifs_writepage,
> @@ -1548,6 +1557,7 @@ const struct address_space_operations ubifs_file_address_operations = {
>   	.invalidatepage = ubifs_invalidatepage,
>   	.set_page_dirty = ubifs_set_page_dirty,
>   	.releasepage    = ubifs_releasepage,
> +	.direct_IO	= ubifs_direct_IO,
>   };
>
>   const struct inode_operations ubifs_file_inode_operations = {
>