From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Kay Sievers <kay.sievers@vrfy.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Greg KH <greg@kroah.com>,
Lennart Poettering <lennart@poettering.net>,
Werner Fink <werner@suse.de>, Jiri Slaby <jslaby@suse.cz>
Subject: Re: tty: add 'active' sysfs attribute to tty0 and console device
Date: Tue, 16 Nov 2010 15:57:17 +0000 [thread overview]
Message-ID: <20101116155717.6671e484@lxorguk.ukuu.org.uk> (raw)
In-Reply-To: <1289922400.1253.3.camel@yio.site>
On Tue, 16 Nov 2010 16:46:40 +0100
Kay Sievers <kay.sievers@vrfy.org> wrote:
> commit be0d5f02c9194fe41c1aad11d7282db117bda938
> Author: Kay Sievers <kay.sievers@vrfy.org>
> Date: Tue Nov 9 18:53:59 2010 +0100
>
> tty: add 'active' sysfs attribute to tty0 and console device
This is all somewhat weird.
> Userspace can query the actual virtual console, and the configured
> console devices behind /dev/tt0 and /dev/console.
All the other vt interface code is in the vt driver, the ioctls for it
are in the vt driver and a query about what is the active vt only has
meaning within that context as you need to post a waitevent first to
track changes during the query. So if you need a VT_GETACTIVE interface
put it in the tty ioctls where it can be properly locked and used.
> +What: /sys/class/tty/tty0/active
> +Date: Nov 2010
> +Contact: Kay Sievers <kay.sievers@vrfy.org>
> +Description:
> + Shows the currently active virtual console
> + device, like 'tty1'.
> + The file supports poll() to detect virtual
> + console switches.
NAK this, its a nonsense interface
Seriously what use is an interface that tells you "what the console might
have been", this is why we have a proper event tracking interface instead.
> +static ssize_t show_cons_active(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct console *cs[16];
> + int i = 0;
> + struct console *c;
> + ssize_t count = 0;
> +
> + acquire_console_sem();
> + for (c = console_drivers; c; c = c->next) {
> + if (!c->device)
> + continue;
> + if (!c->write)
> + continue;
> + if ((c->flags & CON_ENABLED) == 0)
> + continue;
> + cs[i++] = c;
> + if (i >= ARRAY_SIZE(cs))
> + break;
> + }
> + while (i--)
> + count += sprintf(buf + count, "%s%d%c",
> + cs[i]->name, cs[i]->index, i ? ' ':'\n');
> + release_console_sem();
> +
> + return count;
> +}
> +static DEVICE_ATTR(active, S_IRUGO, show_cons_active, NULL);
This makes more sense.
> - device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL,
> - "tty");
> + device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");
Please keep unneccessary reformatting patches out of code changes, submit
them separately.
> static ATOMIC_NOTIFIER_HEAD(vt_notifier_list);
> @@ -688,6 +696,8 @@ void redraw_screen(struct vc_data *vc, int is_switch)
> save_screen(old_vc);
> set_origin(old_vc);
> }
> + if (tty0dev)
> + sysfs_notify(&tty0dev->kobj, NULL, "active");
What is the locking on tty0dev at this point ? Wrong place anyway - we
have vt change notifiers that do this properly and can track other
changes like console sizes, add and remove. See the VT_WAITACTIVE stuff
etc.
> +static ssize_t show_tty_active(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "tty%d\n", fg_console + 1);
> +}
> +static DEVICE_ATTR(active, S_IRUGO, show_tty_active, NULL);
How do you ensure fg_console returned to user space is right when the
console can change during and after the call ?
next prev parent reply other threads:[~2010-11-16 15:58 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-16 15:46 tty: add 'active' sysfs attribute to tty0 and console device Kay Sievers
2010-11-16 15:57 ` Alan Cox [this message]
2010-11-16 16:13 ` Kay Sievers
2010-11-16 17:14 ` Alan Cox
2010-11-16 18:51 ` Kay Sievers
2010-11-16 19:55 ` Alan Cox
2010-11-16 20:15 ` Kay Sievers
2010-11-16 20:49 ` Alan Cox
2010-11-16 21:29 ` Kay Sievers
2010-11-16 21:42 ` Lennart Poettering
2010-11-16 22:51 ` Alan Cox
2010-11-16 22:58 ` Lennart Poettering
2010-11-16 23:04 ` Alan Cox
2010-11-16 23:18 ` Lennart Poettering
2010-11-16 23:49 ` Etched Pixels
2010-11-16 21:36 ` Lennart Poettering
2010-11-16 22:56 ` Alan Cox
2010-11-16 23:10 ` Lennart Poettering
2010-11-16 23:45 ` Alan Cox
2010-11-17 16:31 ` John Stoffel
2010-11-17 22:01 ` Valdis.Kletnieks
2010-11-17 23:40 ` Kay Sievers
2010-11-17 23:56 ` Alan Cox
2010-11-18 1:27 ` Greg KH
2010-11-18 1:48 ` Lennart Poettering
2010-11-18 1:53 ` Greg KH
2010-11-18 2:29 ` Lennart Poettering
2010-11-18 11:00 ` Dr. Werner Fink
2010-11-18 11:23 ` Alan Cox
2010-11-18 12:12 ` Dr. Werner Fink
2010-11-18 12:58 ` Alan Cox
2010-11-18 13:14 ` Dr. Werner Fink
2010-11-18 14:41 ` Alan Cox
2010-11-19 13:21 ` Dr. Werner Fink
2010-11-19 15:47 ` Alan Cox
2010-11-19 17:07 ` Dr. Werner Fink
2010-11-19 18:02 ` Greg KH
2010-11-19 18:41 ` Dr. Werner Fink
2010-11-20 12:40 ` Alan Cox
2010-12-01 11:15 ` Dr. Werner Fink
2010-11-18 12:04 ` Kay Sievers
2010-11-18 10:15 ` Alan Cox
2010-11-18 11:55 ` Kay Sievers
2010-11-18 13:01 ` Alan Cox
[not found] <20101201112004.12d78cd7@lxorguk.ukuu.org.uk>
2010-12-01 12:32 ` Dr. Werner Fink
[not found] ` <tiocgdev1@mdm.bga.com>
2010-12-03 11:48 ` Dr. Werner Fink
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