[dm-devel] [PATCH V5 08/12] block: use per-task poll context to implement bio based io polling

[Christoph Hellwig]

> +static int blk_bio_poll_io(struct io_context *submit_ioc,
> +		struct io_context *poll_ioc)

Givem that poll_ioc is always current->io_context there is no
need to pass it.

> +	struct blk_bio_poll_ctx *poll_ctx = poll_ioc ?
> +		poll_ioc->data : NULL;

and it really should not be NULL here, should it?

> +static int __blk_bio_poll(blk_qc_t cookie)
> +{
> +	struct io_context *poll_ioc = current->io_context;
> +	pid_t pid;
> +	struct task_struct *submit_task;
> +	int ret;
> +
> +	pid = (pid_t)cookie;
> +
> +	/* io poll often share io submission context */
> +	if (likely(current->pid == pid && blk_bio_ioc_valid(current)))
> +		return blk_bio_poll_io(poll_ioc, poll_ioc);
> +
> +	submit_task = find_get_task_by_vpid(pid);
> +	if (likely(blk_bio_ioc_valid(submit_task)))
> +		ret = blk_bio_poll_io(submit_task->io_context, poll_ioc);
> +	else
> +		ret = 0;
> +	if (likely(submit_task))
> +		put_task_struct(submit_task);

Wouldn't it make more sense to just store the submitting context
in the bio, even if that uses more space?  Having to call
find_get_task_by_vpid in the poll context seems rather problematic.

Note that this requires doing the refacoring to get rid of the separate
blk_qc_t passed up the stack I asked for earlier, but hiding all these
details seems like a really useful change anyway.