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From: Arnd Bergmann <arnd@arndb.de>
To: linuxppc-dev@ozlabs.org
Subject: Re: [patch 5/7] ps3: Disk Storage Driver
Date: Fri, 25 May 2007 18:26:25 +0200
References: <20070525083607.784351000@sonycom.com>
	<20070525083632.575306000@sonycom.com>
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Message-Id: <200705251826.25572.arnd@arndb.de>
Cc: Geert.Uytterhoeven@sonycom.com, linux-kernel@vger.kernel.org
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On Friday 25 May 2007, Geert.Uytterhoeven@sonycom.com wrote:
> +static void ps3disk_scatter_gather(struct ps3_storage_device *dev,
> +				   struct request *req, int gather)
> +{
> +	unsigned int sectors = 0, offset = 0;
> +	struct bio *bio;
> +	sector_t sector;
> +	struct bio_vec *bvec;
> +	unsigned int i = 0, j;
> +	size_t size;
> +	void *buf;
> +
> +	rq_for_each_bio(bio, req) {
> +		sector = bio->bi_sector;
> +		dev_dbg(&dev->sbd.core,
> +			"%s:%u: bio %u: %u segs %u sectors from %lu\n",
> +			__func__, __LINE__, i, bio_segments(bio),
> +			bio_sectors(bio), sector);
> +		bio_for_each_segment(bvec, bio, j) {
> +			size = bio_cur_sectors(bio)*KERNEL_SECTOR_SIZE;
> +			buf = __bio_kmap_atomic(bio, j, KM_USER0);
> +			if (gather)
> +				memcpy(dev->bounce_buf+offset, buf, size);
> +			else
> +				memcpy(buf, dev->bounce_buf+offset, size);
> +			offset += size;
> +			__bio_kunmap_atomic(bio, KM_USER0);
> +		}
> +		sectors += bio_sectors(bio);
> +		i++;
> +	}
> +}

So the hypervison uses guest-real addresses here? I would have expected
it to use the kernel page tables, which lets you use vmap() to do
scatter-gather.

> +static int ps3disk_thread(void *data)
> +{
> +	struct ps3_storage_device *dev = data;
> +	struct ps3disk_private *priv = ps3disk_priv(dev);
> +	request_queue_t *q = priv->queue;
> +	struct request *req;
> +
> +	dev_dbg(&dev->sbd.core, "%s thread init\n", __func__);
> +
> +	current->flags |= PF_NOFREEZE;
> +
> +	while (!kthread_should_stop()) {
> +		spin_lock_irq(&priv->lock);
> +		set_current_state(TASK_INTERRUPTIBLE);
> +		req = elv_next_request(q);
> +		if (!req) {
> +			spin_unlock_irq(&priv->lock);
> +			schedule();
> +			continue;
> +		}
> +		if (!blk_fs_request(req)) {
> +			blk_dump_rq_flags(req, DEVICE_NAME " bad request");
> +			end_request(req, 0);
> +			spin_unlock_irq(&priv->lock);
> +			continue;
> +		}
> +		spin_unlock_irq(&priv->lock);
> +		ps3disk_handle_request_sg(dev, req);
> +	}
> +
> +	dev_dbg(&dev->sbd.core, "%s thread exit\n", __func__);
> +	return 0;
> +}

I don't really understand what the kthread is needed for. You probably
thought about multiple options and ended up with this, but having
a comment in front of it might be helpful.

	Arnd <><