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Message-ID: <482F5113.5090703@cosmosbay.com>
Date: Sat, 17 May 2008 23:41:39 +0200
From: Eric Dumazet <dada1@...mosbay.com>
To: James Cammarata <jimi@...x.net>
Cc: linux-kernel@...r.kernel.org,
Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH updated] net: add ability to clear per-interface network
statistics via procfs
James Cammarata a écrit :
>> 1) Every call to get_proc_net() should be paired with a call to
>> put_net(), or else you leak struct net.
>
> My mistake, I will add this and resubmit.
>
This version has a bug, please check again.
>> 2) I am not sure this is the right way to do this... Did you consider
>> to extend ethtool instead ?
>
> Yes, I did consider that. My reasoning for adding it to procfs is
> that each
> driver defines their own ethtool interface, so it was much simpler to
> add it here, with a lot less code changes and broader support.
>
Maybe much simpler but looks like a hack...
>
> ---
>
> --- linux-2.6.25.4/net/core/dev.c 2008-05-15 10:00:12.000000000
> -0500
> +++ linux-2.6.25.4-jcammara/net/core/dev.c 2008-05-17
> 09:50:22.000000000 -0500
> @@ -2455,2 +2455,80 @@
>
> +/**
> + * 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))
net is not initialized so you will call put_net(garbage) and crash
My suggestion was better, since you dont have to test if (net) ,
just call put_net(net) at the right place (before out: label)
> + 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;
> + if(sscanf(p,"%16s",devname)>0) {
> + dev = dev_get_by_name(net,devname);
> + if (dev) {
> + if (dev->get_stats) {
> + struct net_device_stats *stats =
> + dev->get_stats(dev);
> + memset(stats,0,
> + sizeof(struct
> net_device_stats));
> + }
> + dev_put(dev);
> + }
> + }
> + }
> +
> + /*
> + * convert success returns so that we return the
> + * number of bytes consumed.
> + */
> + if (!err)
> + err = length;
> +
> + out:
> + if(net)
> + put_net(net);
> + free_page((unsigned long)buffer);
> + return err;
> +}
> +
> static void *softnet_seq_start(struct seq_file *seq, loff_t *pos)
> @@ -2498,2 +2576,3 @@
> .read = seq_read,
> + .write = proc_net_dev_write,
> .llseek = seq_lseek,
>
>
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