[PATCH] net: add ability to clear per-interface network statistics via procfs

["Cammarata, James" <James.Cammarata@savvis.net>]

From: James Cammarata <jimi@sngx.net>

Added the ability to write to /proc/net/dev in order to clear the
interface counters for a given interface.  The ability to zero out
counters (especially the error counters) is extremely useful when
troubleshooting interface issues.

Syntax:
  echo 'net clear-stats ifdev' > /proc/net/dev
Where "ifdev" is the device name you wish to clear.

This code is based mainly on the code found in drivers/scsi/scsi_proc.c

Signed-off-by: James Cammarata <jimi@sngx.net>
---

--- net/core/dev.original       2008-05-13 12:48:46.000000000 -0400
+++ net/core/dev.c      2008-05-13 13:17:15.000000000 -0400
@@ -2453,6 +2453,87 @@ static struct netif_rx_stats *softnet_ge
        return rc;
 }

+/**
+ * proc_net_dev_write - handle writes to /proc/net/dev
+ * @file: not used
+ * @buf: buffer to write
+ * @length: length of buf, at most PAGE_SIZE
+ * @ppos: not used
+ *
+ * Description: this provides a mechanism to clear statistics on a
+ * per-interface basis
+ * "echo 'net clear-stats ifdev' >/proc/net/dev"
+ * with  "ifdev" replaced by the device name you wish to clear.
+ *
+ */
+static ssize_t proc_net_dev_write(struct file *file, const char __user
*buf,
+                                  size_t length, loff_t *ppos)
+{
+        char *buffer, *p;
+        char devname[IFNAMSIZ];
+        struct net *net;
+        struct net_device *dev;
+        int err;
+
+        if (!buf || length > PAGE_SIZE)
+                return -EINVAL;
+
+        buffer = (char *)__get_free_page(GFP_KERNEL);
+        if (!buffer)
+                return -ENOMEM;
+
+        err = -EFAULT;
+        if (copy_from_user(buffer, buf, length))
+                goto out;
+
+        err = -EINVAL;
+        if (length < PAGE_SIZE)
+                buffer[length] = '\0';
+        else if (buffer[PAGE_SIZE-1])
+                goto out;
+
+        err = -ENXIO;
+        net = get_proc_net(file->f_dentry->d_inode);
+        if (!net)
+                goto out;
+
+        /*
+         * Usage: echo "net clear-stats ifdev" >/proc/net/dev
+         * with  "ifdev" replaced by the device name you wish to clear.
+         */
+        if (!strncmp("net clear-stats",buffer,15)) {
+                p = buffer + 16;
+                sscanf(p,"%s",devname);
+                printk(KERN_INFO "net clearing stats - device is:
%s\n", devname);
+                dev = dev_get_by_name(net,devname);
+                if (!dev) {
+                   printk(KERN_INFO "no interface named '%s'\n",
devname);
+                } else {
+                        if (dev->get_stats) {
+                                struct net_device_stats *stats =
dev->get_stats(dev);
+                                memset(stats,0,sizeof(struct
net_device_stats));
+                                printk(KERN_INFO "stats cleared for
interface %s\n", devname);
+                        } else {
+                                printk(KERN_INFO "%s has no stats to
clear\n", devname);
+                        }
+                        dev_put(dev);
+                }
+        }
+
+        /*
+         * convert success returns so that we return the
+         * number of bytes consumed.
+         */
+        if (!err)
+                err = length;
+
+ out:
+        free_page((unsigned long)buffer);
+        return err;
+}
+
 static void *softnet_seq_start(struct seq_file *seq, loff_t *pos)
 {
        return softnet_get_online(pos);
@@ -2496,6 +2577,7 @@ static const struct file_operations dev_
        .owner   = THIS_MODULE,
        .open    = dev_seq_open,
        .read    = seq_read,
+        .write   = proc_net_dev_write,
        .llseek  = seq_lseek,
        .release = seq_release_net,
 };

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