From mboxrd@z Thu Jan  1 00:00:00 1970
From: bjorn@mork.no (=?utf-8?Q?Bj=C3=B8rn_Mork?=)
Date: Tue, 27 May 2014 14:59:56 +0200
Subject: Simple Misc Driver - Problem with string copy to user
In-Reply-To: <CAJyon0uo=TH_rS-zx_nr2G-nJDLAiWGuc=MDc1aVo7y96grwng@mail.gmail.com>
	(Lucas Tanure's message of "Tue, 27 May 2014 09:48:43 -0300")
References: <CAJyon0uo=TH_rS-zx_nr2G-nJDLAiWGuc=MDc1aVo7y96grwng@mail.gmail.com>
Message-ID: <87ppizgywj.fsf@nemi.mork.no>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

Lucas Tanure <tanure@linux.com> writes:

>> What is worg with my read operation?
>
> static ssize_t
> misc_drv_read(struct file *filp, char __user * buf, size_t count, loff_t *
> offp){
>     int nbytes;
> char * string = "hello World";
> nbytes = copy_to_user(buf, string, 12);
>  return nbytes;
> }

copy_to_user returns the number of bytes which could *not* be copied.
So it will return 0 on success, making your read return 0.


Bj?rn