linux-kernel - Re: [Xen-devel] [PATCH net-next v3] xen-netback: Adding debugfs "io_ring

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Date:	Tue, 8 Jul 2014 19:43:16 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>
Subject: Re: [Xen-devel] [PATCH net-next v3] xen-netback: Adding debugfs "io_ring_qX"
 files

On 08/07/14 18:39, Konrad Rzeszutek Wilk wrote:

>
>
>> +	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?
Indeed, I've just copy-pasted that snippet you wrote in your prev mail 
and I haven't tried it out, as it was a very small change. I'll fix it.

>> +
>>   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
It wouldn't change the end result, but from the code reader's point of 
view the current way is a little bit better, as (s)he doesn't need to 
check the declaration to realize it has effect only if that config 
option is enabled.

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