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

From: Zoltan Kiss
Date: Tue Jul 08 2014 - 14:43:45 EST

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) {
+ 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:

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