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Date: Fri, 7 Jun 2013 11:40:25 +0200
From: Johan Hovold <jhovold@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Tobias Winter <tobias@...uxdingsda.de>,
Bjørn Mork <bjorn@...k.no>,
Rob Landley <rob@...dley.net>,
Johan Hovold <jhovold@...il.com>, linux-usb@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] USB: serial: make minor allocation dynamic
On Thu, Jun 06, 2013 at 10:31:21AM -0700, Greg KH wrote:
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[...]
> --- a/drivers/usb/serial/usb-serial.c
> +++ b/drivers/usb/serial/usb-serial.c
> @@ -37,6 +37,7 @@
> #include <linux/usb.h>
> #include <linux/usb/serial.h>
> #include <linux/kfifo.h>
> +#include <linux/idr.h>
> #include "pl2303.h"
>
> #define DRIVER_AUTHOR "Greg Kroah-Hartman <gregkh@...uxfoundation.org>"
> @@ -49,72 +50,75 @@
> drivers depend on it.
> */
>
> -static struct usb_serial *serial_table[SERIAL_TTY_MINORS];
> +static DEFINE_IDR(serial_minors);
> static DEFINE_MUTEX(table_lock);
> static LIST_HEAD(usb_serial_driver_list);
>
> /*
> - * Look up the serial structure. If it is found and it hasn't been
> + * Look up the serial port structure. If it is found and it hasn't been
> * disconnected, return with its disc_mutex held and its refcount
Second sentence needs to be updated as well as it is the disc_mutex and
refcount of the owning usb_serial struct we're referring to.
> * incremented. Otherwise return NULL.
> */
> -struct usb_serial *usb_serial_get_by_index(unsigned index)
> +struct usb_serial_port *usb_serial_port_get_by_minor(unsigned minor)
> {
> - struct usb_serial *serial;
> + struct usb_serial *serial = NULL;
> + struct usb_serial_port *port;
>
> mutex_lock(&table_lock);
> - serial = serial_table[index];
> + port = idr_find(&serial_minors, minor);
> + if (!port)
> + goto exit;
>
> - if (serial) {
> - mutex_lock(&serial->disc_mutex);
> - if (serial->disconnected) {
> - mutex_unlock(&serial->disc_mutex);
> - serial = NULL;
> - } else {
> - kref_get(&serial->kref);
> - }
> + serial = port->serial;
> + mutex_lock(&serial->disc_mutex);
> + if (serial->disconnected) {
> + mutex_unlock(&serial->disc_mutex);
> + serial = NULL;
You want to set port rather than serial to NULL here now.
> + } else {
> + kref_get(&serial->kref);
> }
> +exit:
> mutex_unlock(&table_lock);
> - return serial;
> + return port;
> }
>
> -static struct usb_serial *get_free_serial(struct usb_serial *serial,
> - int num_ports, unsigned int *minor)
> +static int get_free_port(struct usb_serial_port *port)
> {
> - unsigned int i, j;
> - int good_spot;
> -
> - dev_dbg(&serial->interface->dev, "%s %d\n", __func__, num_ports);
> + int i;
>
> - *minor = 0;
> mutex_lock(&table_lock);
> - for (i = 0; i < SERIAL_TTY_MINORS; ++i) {
> - if (serial_table[i])
> - continue;
> + i = idr_alloc(&serial_minors, port, 0, 0, GFP_KERNEL);
> + if (i < 0)
> + goto exit;
> + port->minor = i;
> +exit:
> + mutex_unlock(&table_lock);
> + return i;
> +}
>
> - good_spot = 1;
> - for (j = 1; j <= num_ports-1; ++j)
> - if ((i+j >= SERIAL_TTY_MINORS) || (serial_table[i+j])) {
> - good_spot = 0;
> - i += j;
> - break;
> - }
> - if (good_spot == 0)
> - continue;
> +static int get_free_serial(struct usb_serial *serial, int num_ports)
> +{
> + unsigned int i;
> + unsigned int j;
> + int x;
>
> - *minor = i;
> - j = 0;
> - dev_dbg(&serial->interface->dev, "%s - minor base = %d\n", __func__, *minor);
> - for (i = *minor; (i < (*minor + num_ports)) && (i < SERIAL_TTY_MINORS); ++i, ++j) {
> - serial_table[i] = serial;
> - serial->port[j]->minor = i;
> - serial->port[j]->port_number = i - *minor;
> - }
> - mutex_unlock(&table_lock);
> - return serial;
> + dev_dbg(&serial->interface->dev, "%s %d\n", __func__, num_ports);
> +
> + for (i = 0; i < num_ports; ++i) {
> + x = get_free_port(serial->port[i]);
> + if (x < 0)
> + goto error;
> + serial->port[i]->port_number = i;
> }
What do you think about removing get_free_port altogether and simply
call idr_alloc directly in the loop above instead? This would have the
benefit of only acquiring the table_lock once per device, which would
also prevent the possibility of higher port numbers receiving smaller
minors (e.g. due to a parallel disconnect).
> + serial->minors_reserved = 1;
> + return 0;
> +error:
> + /* unwind the already allocated minors */
> + mutex_lock(&table_lock);
> + for (j = 0; j < i; ++j)
> + idr_remove(&serial_minors, serial->port[j]->minor);
> mutex_unlock(&table_lock);
> - return NULL;
> + return x;
> }
[...]
> --- a/include/linux/usb/serial.h
> +++ b/include/linux/usb/serial.h
> @@ -21,7 +21,6 @@
>
> #define SERIAL_TTY_MAJOR 188 /* Nice legal number now */
> #define SERIAL_TTY_MINORS 254 /* loads of devices :) */
> -#define SERIAL_TTY_NO_MINOR 255 /* No minor was assigned */
>
> /* The maximum number of ports one device can grab at once */
> #define MAX_NUM_PORTS 8
> @@ -142,7 +141,6 @@ static inline void usb_set_serial_port_d
> * @dev: pointer to the struct usb_device for this device
> * @type: pointer to the struct usb_serial_driver for this device
> * @interface: pointer to the struct usb_interface for this device
> - * @minor: the starting minor number for this device
> * @num_ports: the number of ports this device has
> * @num_interrupt_in: number of interrupt in endpoints we have
> * @num_interrupt_out: number of interrupt out endpoints we have
> @@ -161,7 +159,7 @@ struct usb_serial {
> unsigned char disconnected:1;
> unsigned char suspending:1;
> unsigned char attached:1;
> - unsigned char minor;
> + unsigned char minors_reserved:1;
> unsigned char num_ports;
> unsigned char num_port_pointers;
> char num_interrupt_in;
> @@ -321,7 +319,7 @@ static inline void usb_serial_console_di
> #endif
>
> /* Functions needed by other parts of the usbserial core */
> -extern struct usb_serial *usb_serial_get_by_index(unsigned int minor);
> +extern struct usb_serial_port *usb_serial_port_get_by_minor(unsigned int minor);
As Tobias already noted, this breaks the USB console driver. However, it
looks like the call in that driver is not really needed and that
therefore usb_serial_port_get_by_minor need not be exported at all.
> extern void usb_serial_put(struct usb_serial *serial);
> extern int usb_serial_generic_open(struct tty_struct *tty,
> struct usb_serial_port *port);
Thanks,
Johan
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