Re: [Xen-devel] [PATCH net-next v4] xen-netback: Adding debugfs "io_ring_qX" files

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Aug 11, 2014 at 11:50:56AM +0100, David Vrabel wrote:
> On 11/08/14 11:38, Wei Liu wrote:
> > On Sun, Aug 10, 2014 at 10:57:51PM +0800, SeeChen Ng wrote:
> >> Hi, I'm a noob to linux kernel, I tried to figure out the usage of the 
> >> function
> >> "simple_write_to_buffer", and I got confused about the code here.
> >>
> >>> +static ssize_t
> >>> +xenvif_write_io_ring(struct file *filp, const char __user *buf, size_t 
> >>> count,
> >>> +                    loff_t *ppos)
> >>> +{
> >>> +       struct xenvif_queue *queue =
> >>> +               ((struct seq_file *)filp->private_data)->private;
> >>> +       int len;
> >>> +       char write[sizeof(XENVIF_KICK_STR)];
> >>> +
> >>> +       /* don't allow partial writes and check the length */
> >>> +       if (*ppos != 0)
> >>> +               return 0;
> >>> +       if (count < sizeof(XENVIF_KICK_STR) - 1)
> >>> +               return -ENOSPC;
> >> The statement here is trying to verify the value of "count" is smaller
> >> than the size of array "write", make sure that the array got
> >> enough space for the write operation, right?
> >>
> > 
> > Yes I think so.
> 
> Is anyone reading the comment?
> 

I read that.

> /* don't allow partial writes and check the length */
> 

"partial writes" -> ppos check
"check the lenght" -> count check

> The sense of the check is correct.
> 

Using -ENOSPC is incorrect for length check IMO.

The following strncmp does the job, if the string written in is not
"kick" it prints out warning.

Wei.

> David

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