Subject: Re: [Xen-devel] [PATCH net-next v3] xen-netback: Adding debugfs "io_ring_qX" files

From: Konrad Rzeszutek Wilk <[email-masked]>
Date: Tue, 8 Jul 2014 13:39:34 -0400

. snip..
>  typedef unsigned int pending_ring_idx_t;
>  #define INVALID_PENDING_RING_IDX (~0U)
> @@ -224,6 +225,10 @@ struct xenvif {
>  	struct xenvif_queue *queues;
>  	unsigned int num_queues; /* active queues, resource allocated */
>  
> +#ifdef CONFIG_DEBUG_FS
> +	struct dentry *xenvif_dbg_root;
> +#endif /* CONFIG_DEBUG_FS */

Usually those sort of comments are good when the code inside the #ifdef
spans more than one page. I think you are on the safe side if you
remove it :-)

> +
>  	/* Miscellaneous private stuff. */
>  	struct net_device *dev;
>  };
> @@ -297,10 +302,16 @@ static inline pending_ring_idx_t nr_pending_reqs(struct xenvif_queue *queue)
>  /* Callback from stack when TX packet can be released */
>  void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success);
>  
> +irqreturn_t xenvif_interrupt(int irq, void *dev_id);
> +
>  extern bool separate_tx_rx_irq;
>  
>  extern unsigned int rx_drain_timeout_msecs;
>  extern unsigned int rx_drain_timeout_jiffies;
>  extern unsigned int xenvif_max_queues;
>  
> +#ifdef CONFIG_DEBUG_FS
> +extern struct dentry *xen_netback_dbg_root;
> +#endif /* CONFIG_DEBUG_FS */

Ditto

> +
>  #endif /* __XEN_NETBACK__COMMON_H__ */
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 9e97c7c..ef75b45 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -102,7 +102,7 @@ static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id)
>  	return IRQ_HANDLED;
>  }
>  
> -static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
> +irqreturn_t xenvif_interrupt(int irq, void *dev_id)
>  {
>  	xenvif_tx_interrupt(irq, dev_id);
>  	xenvif_rx_interrupt(irq, dev_id);
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 1844a47..77127ca 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -1987,6 +1987,13 @@ static int __init netback_init(void)
>  
>  	rx_drain_timeout_jiffies = msecs_to_jiffies(rx_drain_timeout_msecs);
>  
> +#ifdef CONFIG_DEBUG_FS
> +	xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
> +	if (IS_ERR_OR_NULL(xen_netback_dbg_root))
> +		pr_warn("Init of debugfs returned %ld!\n",
> +			PTR_ERR(xen_netback_dbg_root));
> +#endif /* CONFIG_DEBUG_FS */
> +
>  	return 0;
>  
>  failed_init:
> @@ -1997,6 +2004,10 @@ module_init(netback_init);
>  
>  static void __exit netback_fini(void)
>  {
> +#ifdef CONFIG_DEBUG_FS
> +	if (!IS_ERR_OR_NULL(xen_netback_dbg_root))
> +		debugfs_remove_recursive(xen_netback_dbg_root);
> +#endif /* CONFIG_DEBUG_FS */
>  	xenvif_xenbus_fini();
>  }
>  module_exit(netback_fini);
> diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
> index 3d85acd..03f9b08 100644
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -44,6 +44,173 @@ static void unregister_hotplug_status_watch(struct backend_info *be);
>  static void set_backend_state(struct backend_info *be,
>  			      enum xenbus_state state);
>  
> +#ifdef CONFIG_DEBUG_FS
> +struct dentry *xen_netback_dbg_root = NULL;
> +
> +static int xenvif_read_io_ring(struct seq_file *m, void *v)
> +{
> +	struct xenvif_queue *queue = m->private;
> +	struct xen_netif_tx_back_ring *tx_ring = &queue->tx;
> +	struct xen_netif_rx_back_ring *rx_ring = &queue->rx;
> +
> +	if (tx_ring->sring) {
> +		struct xen_netif_tx_sring *sring = tx_ring->sring;
> +
> +		seq_printf(m, "Queue %d\nTX: nr_ents %u\n", queue->id,
> +			   tx_ring->nr_ents);
> +		seq_printf(m, "req prod %u (%d) cons %u (%d) event %u (%d)\n",
> +			   sring->req_prod,
> +			   sring->req_prod - sring->rsp_prod,
> +			   tx_ring->req_cons,
> +			   tx_ring->req_cons - sring->rsp_prod,
> +			   sring->req_event,
> +			   sring->req_event - sring->rsp_prod);
> +		seq_printf(m, "rsp prod %u (base) pvt %u (%d) event %u (%d)\n",
> +			   sring->rsp_prod,
> +			   tx_ring->rsp_prod_pvt,
> +			   tx_ring->rsp_prod_pvt - sring->rsp_prod,
> +			   sring->rsp_event,
> +			   sring->rsp_event - sring->rsp_prod);
> +		seq_printf(m, "pending prod %u pending cons %u nr_pending_reqs %u\n",
> +			   queue->pending_prod,
> +			   queue->pending_cons,
> +			   nr_pending_reqs(queue));
> +		seq_printf(m, "dealloc prod %u dealloc cons %u dealloc_queue %u\n\n",
> +			   queue->dealloc_prod,
> +			   queue->dealloc_cons,
> +			   queue->dealloc_prod - queue->dealloc_cons);
> +	}
> +
> +	if (rx_ring->sring) {
> +		struct xen_netif_rx_sring *sring = rx_ring->sring;
> +
> +		seq_printf(m, "RX: nr_ents %u\n", rx_ring->nr_ents);
> +		seq_printf(m, "req prod %u (%d) cons %u (%d) event %u (%d)\n",
> +			   sring->req_prod,
> +			   sring->req_prod - sring->rsp_prod,
> +			   rx_ring->req_cons,
> +			   rx_ring->req_cons - sring->rsp_prod,
> +			   sring->req_event,
> +			   sring->req_event - sring->rsp_prod);
> +		seq_printf(m, "rsp prod %u (base) pvt %u (%d) event %u (%d)\n\n",
> +			   sring->rsp_prod,
> +			   rx_ring->rsp_prod_pvt,
> +			   rx_ring->rsp_prod_pvt - sring->rsp_prod,
> +			   sring->rsp_event,
> +			   sring->rsp_event - sring->rsp_prod);
> +	}
> +
> +	seq_printf(m, "NAPI state: %lx NAPI weight: %d TX queue len %u\n"
> +		   "Credit timer_pending: %d, credit: %lu, usec: %lu\n"
> +		   "remaining: %lu, expires: %lu, now: %lu\n",
> +		   queue->napi.state, queue->napi.weight,
> +		   skb_queue_len(&queue->tx_queue),
> +		   timer_pending(&queue->credit_timeout),
> +		   queue->credit_bytes,
> +		   queue->credit_usec,
> +		   queue->remaining_credit,
> +		   queue->credit_timeout.expires,
> +		   jiffies);
> +
> +	return 0;
> +}
> +
> +#define XENVIF_KICK_STR "kick"
> +
> +static ssize_t
> +xenvif_write_io_ring(struct file *filp, const char __user *buf, size_t count,
> +		     loff_t *ppos)
> +{
> +	struct xenvif_queue *queue =
> +		((struct seq_file *)filp->private_data)->private;
> +	int len;
> +	char write[sizeof(XENVIF_KICK_STR)];
> +
> +	/* don't allow partial writes and check the length */
> +	if (*ppos != 0)
> +		return 0;
> +	if (count < sizeof(XENVIF_KICK_STR) - 1)
> +		return -ENOSPC;
> +
> +	len = simple_write_to_buffer(write,
> +				     sizeof(write),
> +				     ppos,
> +				     buf,
> +				     count);
> +	if (len < 0)
> +		return len;
> +
> +	if (!strncmp(write, XENVIF_KICK_STR, sizeof(XENVIF_KICK_STR) - 1))
> +		xenvif_interrupt(0, (void *)queue);
> +	else
> +		pr_warn("Unknown command to io_ring_q%d. Available: kick\n",
> +			queue->id);

count = -EINVAL;

> +	return count;
> +}
> +
> +static int xenvif_dump_open(struct inode *inode, struct file *filp)
> +{
> +	int ret;
> +	void *queue = NULL;
> +
> +	if (inode->i_private)
> +		queue = inode->i_private;
> +	ret = single_open(filp, xenvif_read_io_ring, queue);
> +	filp->f_mode |= FMODE_PWRITE;
> +	return ret;
> +}
> +
> +static const struct file_operations xenvif_dbg_io_ring_ops_fops = {
> +	.owner = THIS_MODULE,
> +	.open = xenvif_dump_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +	.write = xenvif_write_io_ring,
> +};
> +
> +static void xenvif_debugfs_addif(struct xenvif_queue *queue)
> +{
> +	struct dentry *pfile;
> +	struct xenvif *vif = queue->vif;
> +	int i;
> +
> +	if (!IS_ERR_OR_NULL(xen_netback_dbg_root))
> +		return;

I am curious to how you tested this patch, as my reading of
the code above would imply that when xen_netback_dbg_root is
initialized - we won't continue within this function?

That '!' should be removed I think.
> +
> +	vif->xenvif_dbg_root = debugfs_create_dir(vif->dev->name,
> +						  xen_netback_dbg_root);
> +	if (!IS_ERR_OR_NULL(vif->xenvif_dbg_root)) {
> +		for (i = 0; i < vif->num_queues; ++i) {
> +			char filename[sizeof("io_ring_q") + 4];
> +
> +			snprintf(filename, sizeof(filename), "io_ring_q%d", i);
> +			pfile = debugfs_create_file(filename,
> +						    S_IRUSR | S_IWUSR,
> +						    vif->xenvif_dbg_root,
> +						    &vif->queues[i],
> +						    &xenvif_dbg_io_ring_ops_fops);
> +			if (IS_ERR_OR_NULL(pfile))
> +				pr_warn("Creation of io_ring file returned %ld!\n",
> +					PTR_ERR(pfile));
> +		}
> +	} else
> +		netdev_warn(vif->dev,
> +			    "Creation of vif debugfs dir returned %ld!\n",
> +			    PTR_ERR(vif->xenvif_dbg_root));
> +}
> +
> +static void xenvif_debugfs_delif(struct xenvif *vif)
> +{
> +	if (!IS_ERR_OR_NULL(xen_netback_dbg_root))

Here that '!'  I think needs to go too.

> +		return;
> +
> +	if (!IS_ERR_OR_NULL(vif->xenvif_dbg_root))
> +		debugfs_remove_recursive(vif->xenvif_dbg_root);
> +	vif->xenvif_dbg_root = NULL;
> +}
> +#endif /* CONFIG_DEBUG_FS */

> +
>  static int netback_remove(struct xenbus_device *dev)
>  {
>  	struct backend_info *be = dev_get_drvdata(&dev->dev);
> @@ -246,8 +413,12 @@ static void backend_create_xenvif(struct backend_info *be)
>  
>  static void backend_disconnect(struct backend_info *be)
>  {
> -	if (be->vif)
> +	if (be->vif) {
> +#ifdef CONFIG_DEBUG_FS
> +		xenvif_debugfs_delif(be->vif);
> +#endif /* CONFIG_DEBUG_FS */

Why don't you just leave it as it (without the #ifdef) and add an
empty function for the #else CONFIG_DEBUG_FS like:

#else
static inline void xenvif_debugfs_addif(struct xenvif_queue *queue) {}
static inline void xenvif_debugfs_delif(struct xenvif *vif) {}
#endif

?
>  		xenvif_disconnect(be->vif);
> +	}
>  }
>  
>  static void backend_connect(struct backend_info *be)
> @@ -560,6 +731,9 @@ static void connect(struct backend_info *be)
>  			be->vif->num_queues = queue_index;
>  			goto err;
>  		}
> +#ifdef CONFIG_DEBUG_FS
> +		xenvif_debugfs_addif(queue);
> +#endif /* CONFIG_DEBUG_FS */

Ditto.
>  	}
>  
>  	/* Initialisation completed, tell core driver the number of
> 
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