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Date: Fri, 7 Jun 2013 10:58:55 -0700
From: Greg KH <gregkh@...uxfoundation.org>
To: Johan Hovold <jhovold@...il.com>
Cc: Tobias Winter <tobias@...uxdingsda.de>,
Bjørn Mork <bjorn@...k.no>,
Rob Landley <rob@...dley.net>, linux-usb@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] USB: serial: make minor allocation dynamic
On Fri, Jun 07, 2013 at 11:40:25AM +0200, Johan Hovold wrote:
> 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.
Good point, now updated.
> > * 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.
Good eye, now fixed.
> > + } 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).
That's a good idea. I've also renamed this function to "allocate_minors"
as that's what it really is doing.
thanks,
greg k-h
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