linux-kernel - Re: [take21 1/4] kevent: Core files.

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Date:	Sat, 28 Oct 2006 14:53:40 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...l.org>, netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Chase Venters <chase.venters@...entec.com>,
	Johann Borck <johann.borck@...sedata.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [take21 1/4] kevent: Core files.

On Sat, Oct 28, 2006 at 12:28:12PM +0200, Eric Dumazet (dada1@...mosbay.com) wrote:
> +/*
> + * Called under kevent_user->ready_lock, so updates are always protected.
> + */
> +int kevent_user_ring_add_event(struct kevent *k)
> +{
> +	unsigned int pidx, off;
> +	struct kevent_mring *ring, *copy_ring;
> +	
> +	ring = k->user->pring[0];
> +
> +	if ((ring->kidx + 1 == ring->uidx) ||
> +			((ring->kidx + 1 == KEVENT_MAX_EVENTS) && ring->uidx 
> == 0)) {
> +		if (k->user->overflow_kevent == NULL)
> +			k->user->overflow_kevent = k;
> +		return -EAGAIN;
> +	}
> +
> 
> 
> I really dont understand how you manage to queue multiple kevents in the 
> 'overflow list'. You just queue one kevent at most. What am I missing ?

There is no overflow list - it is a pointer to the first kevent in the
ready queue, which was not put into ring buffer. It is an optimisation, 
which allows to not search for that position each time new event should 
be placed into the buffer, when it starts to have an empty slot.
 
> 
> >+
> >+	for (i=0; i<KEVENT_MAX_PAGES; ++i) {
> >+		u->pring[i] = (struct kevent_mring 
> >*)__get_free_page(GFP_KERNEL);
> >+		if (!u->pring[i])
> >+			break;
> >+	}
> >+
> >+	if (i != KEVENT_MAX_PAGES)
> >+		goto err_out_free;
> 
> Why dont you use goto directly ?
> 
> 	if (!u->pring[i])
> 		goto err_out_free;
> 
 
I used a fallback mode here which allowed to use smaller number of pages
for kevent ring buffer, but then decided to drop it.
So it is possible to use goto directly.
 
> >+
> >+	u->pring[0]->uidx = u->pring[0]->kidx = 0;
> >+
> >+	return 0;
> >+
> >+err_out_free:
> >+	for (i=0; i<KEVENT_MAX_PAGES; ++i) {
> >+		if (!u->pring[i])
> >+			break;
> >+
> >+		free_page((unsigned long)u->pring[i]);
> >+	}
> >+	return k;
> >+}
> >+
> 
> 
> 
> 
> >+static int kevent_user_ctl_add(struct kevent_user *u, unsigned int num, 
> >void __user *arg)
> >+{
> >+	int err, cerr = 0, knum = 0, rnum = 0, i;
> >+	void __user *orig = arg;
> >+	struct ukevent uk;
> >+
> >+	mutex_lock(&u->ctl_mutex);
> >+
> >+	err = -EINVAL;
> >+	if (num > KEVENT_MIN_BUFFS_ALLOC) {
> >+		struct ukevent *ukev;
> >+
> >+		ukev = kevent_get_user(num, arg);
> >+		if (ukev) {
> >+			for (i = 0; i < num; ++i) {
> >+				err = kevent_user_add_ukevent(&ukev[i], u);
> >+				if (err) {
> >+					kevent_stat_im(u);
> >+					if (i != rnum)
> >+						memcpy(&ukev[rnum], 
> >&ukev[i], sizeof(struct ukevent));
> >+					rnum++;
> >+				} else
> >+					knum++;
> 
> 
> Why are you using/counting knum ?
 
It should go avay. 
 
> >+			}
> >+			if (copy_to_user(orig, ukev, rnum*sizeof(struct 
> >ukevent)))
> >+				cerr = -EFAULT;
> >+			kfree(ukev);
> >+			goto out_setup;
> >+		}
> >+	}
> >+
> >+	for (i = 0; i < num; ++i) {
> >+		if (copy_from_user(&uk, arg, sizeof(struct ukevent))) {
> >+			cerr = -EFAULT;
> >+			break;
> >+		}
> >+		arg += sizeof(struct ukevent);
> >+
> >+		err = kevent_user_add_ukevent(&uk, u);
> >+		if (err) {
> >+			kevent_stat_im(u);
> >+			if (copy_to_user(orig, &uk, sizeof(struct ukevent))) 
> >{
> >+				cerr = -EFAULT;
> >+				break;
> >+			}
> >+			orig += sizeof(struct ukevent);
> >+			rnum++;
> >+		} else
> >+			knum++;
> >+	}
> >+
> >+out_setup:
> >+	if (cerr < 0) {
> >+		err = cerr;
> >+		goto out_remove;
> >+	}
> >+
> >+	err = rnum;
> >+out_remove:
> >+	mutex_unlock(&u->ctl_mutex);
> >+
> >+	return err;
> >+}
> -
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-- 
	Evgeniy Polyakov
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