linux-kernel - Re: [PATCH v2] net/9p/trans_virtio.c: add null terminal for mount tag

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Date:   Thu, 2 Aug 2018 09:59:38 +0800
From:   piaojun <piaojun@...wei.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "Eric Van Hensbergen" <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        "Latchesar Ionkov" <lucho@...kov.net>, Greg Kurz <groug@...d.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        <v9fs-developer@...ts.sourceforge.net>
Subject: Re: [PATCH v2] net/9p/trans_virtio.c: add null terminal for mount tag

Hi Dominique,

On 2018/8/2 9:54, Dominique Martinet wrote:
> piaojun wrote on Thu, Aug 02, 2018:
>> chan->tag is Non-null terminated which will result in printing messy code
>> when debugging code. So we should add '\0' for tag to make the code more
>> convenient and robust. In addition, I drop char->tag_len to simplify the
>> code.
> 
> Some new lines in commit message would be appreciated.
> 
> That aside, I have a couple of nitpicks, but it looks good to me - thanks
> 
>>
>> Signed-off-by: Jun Piao <piaojun@...wei.com>
>> ---
>>  net/9p/trans_virtio.c | 15 +++++----------
>>  1 file changed, 5 insertions(+), 10 deletions(-)
>>
>> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
>> index d422bfc..0fe9c37 100644
>> --- a/net/9p/trans_virtio.c
>> +++ b/net/9p/trans_virtio.c
>> @@ -89,10 +89,8 @@ struct virtio_chan {
>>  	unsigned long p9_max_pages;
>>  	/* Scatterlist: can be too big for stack. */
>>  	struct scatterlist sg[VIRTQUEUE_NUM];
>> -
>> -	int tag_len;
>>  	/*
>> -	 * tag name to identify a mount Non-null terminated
>> +	 * tag name to identify a mount null terminated
>>  	 */
>>  	char *tag;
>>
>> @@ -529,10 +527,9 @@ static ssize_t p9_mount_tag_show(struct device *dev,
>>  	vdev = dev_to_virtio(dev);
>>  	chan = vdev->priv;
>>
>> -	memcpy(buf, chan->tag, chan->tag_len);
>> -	buf[chan->tag_len] = 0;
>> +	memcpy(buf, chan->tag, strlen(chan->tag) + 1);
>>
>> -	return chan->tag_len + 1;
>> +	return strlen(chan->tag) + 1;
> 
> Use a local variable for strlen(chan->tag)?
> 
Yes, local variable looks better.

>>  }
>>
>>  static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);
>> @@ -585,7 +582,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>  		err = -EINVAL;
>>  		goto out_free_vq;
>>  	}
>> -	tag = kmalloc(tag_len, GFP_KERNEL);
>> +	tag = kzalloc(tag_len + 1, GFP_KERNEL);
>>  	if (!tag) {
>>  		err = -ENOMEM;
>>  		goto out_free_vq;
>> @@ -594,7 +591,6 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>  	virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
>>  			   tag, tag_len);
>>  	chan->tag = tag;
>> -	chan->tag_len = tag_len;
>>  	err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
>>  	if (err) {
>>  		goto out_free_tag;
>> @@ -654,8 +650,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>>
>>  	mutex_lock(&virtio_9p_lock);
>>  	list_for_each_entry(chan, &virtio_chan_list, chan_list) {
>> -		if (!strncmp(devname, chan->tag, chan->tag_len) &&
>> -		    strlen(devname) == chan->tag_len) {
>> +		if (!strncmp(devname, chan->tag, strlen(chan->tag) + 1)) {
> 
> strncmp(x, y, strlen(y)+1) is precisely what strcmp does so let's use
> the simpler version
> 
strcmp looks simpler, and I will wait for a while to hear more
suggestions, and then post another patch for these fixes.

Thanks,
Jun