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Date: Tue, 4 Jun 2013 13:04:01 +0200
From: Johan Hovold <jhovold@...il.com>
To: Greg KH <greg@...ah.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: [RFC] raise the maximum number of usb-serial devices to 512
On Mon, Jun 03, 2013 at 07:49:59PM -0700, Greg KH wrote:
> On Mon, May 27, 2013 at 02:28:51PM +0200, Bjørn Mork wrote:
> > But, IMHO, a nicer approach would be to make the allocation completely
> > dynamic, using e.g. the idr subsystem. Static tables are always feel
> > like straight jackets to me, no matter how big they are :)
>
> You are right, I didn't change the code to use idr (it predates idr by
> about a decade or so), because I thought we needed the "rage" logic that
> the usb-serial minor reservation does.
>
> But I'm not so sure anymore, so here's a patch to change to use the idr
> code, and should remove all minor number limitations (well 65k is the
> limit the tty core should be setting I think.)
>
> Tobias, can you test this patch out? Note, I only compiled it, did not
> get the chance to actually run it, so it might not work at all.
I'm afraid this won't work in it's current form. Several drivers and
parts of usb-serial core still depend on the minor numbers being
consecutive for multi-port devices. There are also still references to
SERIAL_TTY_NO_MINOR (255) as well as SERIAL_TTY_MINORS that need to be
addressed.
>
> thanks,
>
> greg k-h
>
> Subject: [PATCH] usb: serial: remove minor number limitation of 255
>
>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> drivers/usb/serial/usb-serial.c | 86 +++++++++++++++++-----------------------
> 1 file changed, 38 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
> index 4753c00..74b6f08 100644
> --- 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>"
> @@ -49,7 +50,7 @@
> 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);
>
> @@ -61,59 +62,52 @@ static LIST_HEAD(usb_serial_driver_list);
> struct usb_serial *usb_serial_get_by_index(unsigned index)
> {
> struct usb_serial *serial;
> + struct usb_serial_port *port;
>
> mutex_lock(&table_lock);
> - serial = serial_table[index];
> -
> - if (serial) {
> - mutex_lock(&serial->disc_mutex);
> - if (serial->disconnected) {
> - mutex_unlock(&serial->disc_mutex);
> - serial = NULL;
> - } else {
> - kref_get(&serial->kref);
> - }
> - }
> + port = idr_find(&serial_minors, index);
> mutex_unlock(&table_lock);
> + if (!port)
> + return NULL;
> +
> + serial = port->serial;
> + kref_get(&serial->kref);
> return serial;
> }
We would still need to handle disconnect, and make sure to return with
the disc_mutex held unless disconnected.
>
> -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)
Missing mutex unlock (as already Dave noted).
> + return -EEXIST;
> + port->number = i;
> + 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 *minor)
> +{
> + unsigned int i;
> + unsigned 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) {
> - serial_table[i] = serial;
> - serial->port[j++]->number = i;
> - }
> - mutex_unlock(&table_lock);
> - return serial;
> + dev_dbg(&serial->interface->dev, "%s %d\n", __func__, num_ports);
> +
> + *minor = 0xffffffff;
> + for (i = 0; i < num_ports; ++i) {
> + x = get_free_port(serial->port[i]);
> + if (x < 0)
> + goto error;
> + if (*minor == 0xffffffff)
> + *minor = x;
> }
> - mutex_unlock(&table_lock);
> - return NULL;
> + return 0;
> +error:
> + // FIXME unwind the already allocated minors
> + return -ENODEV;
> }
As mentioned above, usb-serial core and several drivers currently depend
on us returning the first minor in a consecutive range. It's mostly used
to determine the per device port index, so storing that index in the port
structure could possibly be sufficient.
>
> static void return_serial(struct usb_serial *serial)
> @@ -122,7 +116,7 @@ static void return_serial(struct usb_serial *serial)
>
> mutex_lock(&table_lock);
> for (i = 0; i < serial->num_ports; ++i)
> - serial_table[serial->minor + i] = NULL;
> + idr_remove(&serial_minors, serial->port[i]->number);
> mutex_unlock(&table_lock);
> }
>
> @@ -1041,7 +1035,7 @@ static int usb_serial_probe(struct usb_interface *interface,
> */
> serial->disconnected = 1;
>
> - if (get_free_serial(serial, num_ports, &minor) == NULL) {
> + if (get_free_serial(serial, num_ports, &minor)) {
> dev_err(ddev, "No more free serial devices\n");
> goto probe_error;
> }
> @@ -1225,7 +1219,6 @@ static struct usb_driver usb_serial_driver = {
>
> static int __init usb_serial_init(void)
> {
> - int i;
> int result;
>
> usb_serial_tty_driver = alloc_tty_driver(SERIAL_TTY_MINORS);
> @@ -1233,9 +1226,6 @@ static int __init usb_serial_init(void)
> return -ENOMEM;
>
> /* Initialize our global data */
You could remove the above comment as well.
> - for (i = 0; i < SERIAL_TTY_MINORS; ++i)
> - serial_table[i] = NULL;
> -
> result = bus_register(&usb_serial_bus_type);
> if (result) {
> pr_err("%s - registering bus driver failed\n", __func__);
Thanks,
Johan
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