Hi,
my guess is your are not returning EOF (= 0). User space expects a
return value of 0 (EOF) to terminate reading. But your code will always
return sizeof("Hello world\n"). A fix would be to not only increment
ppos, but also check if it's already behind your data.
Regards,
Martin
Am 30.04.19 um 13:45 schrieb rdq@xxxxxxxxxxx:
> 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;
> }
>
>
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>
--
Dipl.-Inf. Martin Christian
Senior Berater Entwicklung Hardware
secunet Security Networks AG
Tel.: +49 201 5454-3612, Fax +49 201 5454-1323
E-Mail: martin.christian@xxxxxxxxxxx
Ammonstraße 74, 01067 Dresden
www.secunet.com
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