Messages in this thread | | | Date | Tue, 16 Nov 2010 15:57:17 +0000 | From | Alan Cox <> | Subject | Re: tty: add 'active' sysfs attribute to tty0 and console device |
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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 ?
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