linux-kernel - Re: [patch 1/2] staging: speakup: add function to convert dev name to number

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Message-ID: <20170614101326.GA7606@kroah.com>
Date:   Wed, 14 Jun 2017 12:13:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     okash.khawaja@...il.com
Cc:     Jiri Slaby <jslaby@...e.com>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        Kirk Reiser <kirk@...sers.ca>, speakup@...ux-speakup.org,
        Chris Brannon <chris@...-brannons.com>
Subject: Re: [patch 1/2] staging: speakup: add function to convert dev name
 to number

On Tue, Jun 13, 2017 at 11:37:03PM +0100, okash.khawaja@...il.com wrote:
> The function converts strings like ttyS0 and ttyUSB0 to dev_t like
> (4, 64) and (188, 0). Subsequent patch in this set will call it to
> convert user-supplied device into device number. The function does
> some basic sanity checks on the string passed in. It currently supports
> ttyS*, ttyUSB* and, for selected synths, lp*.
> 
> In order to do this, the patch also introduces a string member variable
> named 'dev' to struct spk_synth. 'dev' represents the device name -
> ttyUSB0 etc - which needs conversion to dev_t.
> 
> Signed-off-by: Okash Khawaja <okash.khawaja@...il.com>
> Reviewed-by: Samuel Thibault <samuel.thibault@...-lyon.org>
> 
> ---
>  drivers/staging/speakup/spk_priv.h  |    2 
>  drivers/staging/speakup/spk_ttyio.c |  105 ++++++++++++++++++++++++++++++++++++
>  drivers/staging/speakup/spk_types.h |    1 
>  3 files changed, 108 insertions(+)
> 
> --- a/drivers/staging/speakup/spk_priv.h
> +++ b/drivers/staging/speakup/spk_priv.h
> @@ -40,6 +40,8 @@
>  
>  #define KT_SPKUP 15
>  #define SPK_SYNTH_TIMEOUT 100000 /* in micro-seconds */
> +#define SYNTH_DEFAULT_DEV "ttyS0"
> +#define SYNTH_DEFAULT_SER 0
>  
>  const struct old_serial_port *spk_serial_init(int index);
>  void spk_stop_serial_interrupt(void);
> --- a/drivers/staging/speakup/spk_ttyio.c
> +++ b/drivers/staging/speakup/spk_ttyio.c
> @@ -7,6 +7,13 @@
>  #include "spk_types.h"
>  #include "spk_priv.h"
>  
> +/* Supported device types */
> +#define DEV_PREFIX_TTYS "ttyS"
> +#define DEV_PREFIX_TTYUSB "ttyUSB"
> +#define DEV_PREFIX_LP "lp"
> +
> +const char *lp_supported[] = { "acntsa", "bns", "dummy", "txprt" };
> +
>  struct spk_ldisc_data {
>  	char buf;
>  	struct semaphore sem;
> @@ -16,6 +23,104 @@ struct spk_ldisc_data {
>  static struct spk_synth *spk_ttyio_synth;
>  static struct tty_struct *speakup_tty;
>  
> +static int name_to_dev(const char *name, dev_t *dev_no)
> +{
> +        int maj = -1, min = -1;
> +
> +        if (strncmp(name, DEV_PREFIX_TTYS, strlen(DEV_PREFIX_TTYS)) == 0) {
> +                if (kstrtoint(name + strlen(DEV_PREFIX_TTYS), 10, &min)) {
> +			pr_err("speakup: Invalid ser param. Must be \
> +					between 0 and 191 inclusive.\n");
> +                        return -EINVAL;
> +                }
> +                maj = 4;
> +
> +                if (min < 0 || min > 191) {
> +			pr_err("speakup: Invalid ser param. Must be \
> +					between 0 and 191 inclusive.\n");
> +                        return -EINVAL;
> +                }
> +                min = min + 64;
> +        } else if (strncmp(name, DEV_PREFIX_TTYUSB, strlen(DEV_PREFIX_TTYUSB))
> +			== 0) {
> +                if (kstrtoint(name + strlen(DEV_PREFIX_TTYUSB), 10, &min)) {
> +                        pr_err("speakup: Invalid ttyUSB number. \
> +					Must be a number from 0 onwards\n");
> +                        return -EINVAL;
> +                }
> +                maj = 188;
> +
> +                if (min < 0) {
> +                        pr_err("speakup: Invalid ttyUSB number. \
> +					Must be a number from 0 onwards\n");
> +                        return -EINVAL;
> +                }
> +        } else if (strncmp(name, DEV_PREFIX_LP, strlen(DEV_PREFIX_LP)) == 0) {
> +                if (kstrtoint(name + strlen(DEV_PREFIX_LP), 10, &min)) {
> +                        pr_warn("speakup: Invalid lp number. \
> +					Must be a number from 0 onwards\n");
> +                        return -EINVAL;
> +                }
> +                maj = 6;
> +
> +                if (min < 0) {
> +                        pr_warn("speakup: Invalid lp number. \
> +					Must be a number from 0 onwards\n");
> +                        return -EINVAL;
> +                }
> +        }
> +
> +        if (maj == -1 || min == -1)
> +                return -EINVAL;
> +
> +        /* if here, maj and min must be valid */
> +        *dev_no = MKDEV(maj, min);
> +
> +        return 0;
> +}

Eeek, no, let's never try to parse strings like this and "figure out"
what major/minor number it is.  That's madness and will break if we ever
make all char majors dynamic (there's a thread on lkml about that.)

Why would the kernel need to know major/minor?  Is it going to open a
device node?  If so, again, crazy stuff, that's not good...

thanks,

greg k-h