linux-kernel - Re: [PATCH net-next] xen-netback: Adding debugfs "io_ring

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Date:	Wed, 2 Jul 2014 11:56:07 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH net-next] xen-netback: Adding debugfs "io_ring_qX" files

On Mon, 2014-06-30 at 21:33 +0100, Zoltan Kiss wrote:
> This patch adds debugfs capabilities to netback. There used to be a similar
> patch floating around for classic kernel, but it used procfs. It is based on a
> very similar blkback patch.
> It creates xen-netback/[vifname]/io_ring_q[queueno] files, reading them output
> various ring variables etc. Writing "kick" into it imitates an interrupt
> happened, it can be useful to check whether the ring is just stalled due to a
> missed interrupt.

Shouldn't there be some CONFIG_XEN_DEBUG_FS ifdefs sprinkled around
here?

> 	if (tx_ring->sring) {
> +		struct xen_netif_tx_sring *sring = tx_ring->sring;
> +
> +		err = snprintf(buf + rv, XEN_NETBACK_DBG_IORING_BUF_SIZE - rv,
> +			       "TX queue %d: nr_ents %u\n", i,
> +			       tx_ring->nr_ents);
> +		if (err >= XEN_NETBACK_DBG_IORING_BUF_SIZE - rv)
> +			return XEN_NETBACK_DBG_IORING_BUF_SIZE;
> +		else
> +			rv += err;

Does debugfs not provide helpers which let this be done in some more
palatable way?

arch/x86/xen/p2m.c seems to use some useful seq_*/single_* helpers for
something very similar and it looks much cleaner.

> +	if (vif->xenvif_dbg_root)

No IS_ERR check?

And in backend_disconnect/connect too.

Ian.

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