Re: [PATCH 07/18] io_uring: support for IO polling

On 1/29/19 10:24 AM, Christoph Hellwig wrote:

quoted

@@ -118,12 +120,16 @@ struct io_kiocb {
 	struct list_head	list;
 	unsigned int		flags;
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+#define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
+#define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
 	u64			user_data;
+	u64			res;

Should this be ret or error instead?  res is kinda off.  A little
comment describing it won't hurt either.  Last but not least with
the actual errno value stored here we probably don't need the
REQ_F_IOPOLL_EAGAIN flag, do we?

Yes good point, that flag pre-dates us having the error in there. I'll
rename the field, too.

quoted

+	/*
+	 * Only spin for completions if we don't have multiple devices hanging
+	 * off our complete list, and we're under the requested amount.
+	 */
+	spin = !ctx->poll_multi_file && (*nr_events < min);

no need for the braces here.

Killed

quoted

+static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
+				long min)
+{
+	int ret;
+
+	do {
+		if (list_empty(&ctx->poll_list))
+			return 0;
+
+		ret = io_do_iopoll(ctx, nr_events, min);
+		if (ret < 0)
+			break;
+	} while (min && *nr_events < min);
+
+	if (ret < 0)
+		return ret;
+
+	return *nr_events < min;

The code looks a little clumsy to me.  Why not:

	while (!list_empty(&ctx->poll_list)) {
		int ret = io_do_iopoll(ctx, nr_events, min);
		if (ret)
			return ret;

		if (!min || *nr_events >= min)
			return 0;
	}

	return 1;

I think you messed up the 0/1 here, how about this:

	while (!list_empty(&ctx->poll_list)) {
		int ret;

		ret = io_do_iopoll(ctx, nr_events, min);
		if (ret < 0)
			return ret;
		if (!min || *nr_events >= min)
			return 1;
	}

	return 0;

-- 
Jens Axboe

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