On Tue, Apr 30, 2019 at 12:45:08PM +0100, rdq@xxxxxxxxxxx wrote:
> Greetings,
>
> My I2C sensor driver has a debugfs entry for development purposes.
> Everything works fine with the exception of the read operation. When 'cat'
> is used, the read operation is called repeatedly and indefinitely. If the
> read() is changed to return 0 then, as expected, nothing is displayed.
>
> The pattern for the implementation is (AFAICT) right out of the book (shown
> below).
>
> What am I missing? Any thoughts much appreciated.
>
> TAIA.
>
> RDQ
>
> static ssize_t sc031gs_reg_read_file(struct file *file, char __user
> *user_buf,
> size_t count, loff_t *ppos)
> {
> char *buf = 0;
> ssize_t total = 0;
> struct sc031gs_dev *sensor = file->private_data;
> if (!sensor)
> return -EINVAL;
> if (*ppos < 0 || !count)
> return -EINVAL;
> buf = kmalloc(count, GFP_KERNEL);
> if (!buf)
> return -ENOMEM;
> total = snprintf(buf,count,"Hello world\n");
> if (total >= 0) {
> if (copy_to_user(user_buf, buf, total)) {
> kfree(buf);
> return -EFAULT;
> }
> *ppos += total;
> }
> kfree(buf);
> return total;
> }
You are returning a "short" read, and then disallowing ppos to be set to
a non-zero value? That's a recipie for disaster :(
Also, you allow userspace to allocate as much memory as it asks for?
Not good :(
Why not just use the simple_read_from_buffer() call? That handles all
of the "housekeeping" for you, and your function can be _much_ simpler.
good luck!
greg k-h
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