[PATCH, RFC, BAD IDEA] /proc/tty/console

[PATCH, RFC, BAD IDEA] /proc/tty/console

[Bill Nottingham]

I'm not seriously proposing this. But, as far as I can tell, this
information isn't exposed to userspace anywhere, and it's a useful
thing to know. I'm certainly open for better ideas on how to expose
this (sysfs attributes? other?)

....

The attached patch adds /proc/tty/console. The contents of it are
simply a description of the current drivers attached to /dev/console.
For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
yield:

# cat /proc/tty/console
unknown             /dev/tty0
serial              /dev/ttyS3

Bill

---
diff -ru linux-2.6.24.noarch/fs/proc/proc_tty.c linux/fs/proc/proc_tty.c
--- linux-2.6.24.noarch/fs/proc/proc_tty.c	2008-02-27 12:50:59.000000000 -0500
+++ linux/fs/proc/proc_tty.c	2008-02-27 12:25:54.000000000 -0500
@@ -6,6 +6,7 @@
 
 #include <asm/uaccess.h>
 
+#include <linux/console.h>
 #include <linux/init.h>
 #include <linux/errno.h>
 #include <linux/time.h>
@@ -129,6 +130,38 @@
 	return seq_open(file, &tty_drivers_op);
 }
 
+static int show_tty_console(struct seq_file *m, void *v)
+{
+	int index;
+	struct console *c;
+
+	for (c = console_drivers; c ; c = c->next) {
+		struct tty_driver *t = NULL;
+		if (!c->device)
+			continue;
+		t = c->device(c, &index);
+		seq_printf(m, "%-20s", t->driver_name ? t->driver_name : "unknown");
+		seq_printf(m, "/dev/%s%d", t->name, c->index);
+		seq_printf(m, "\n");
+	}
+	return 0;
+}
+
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+	return *pos == 0 ? &c_start : NULL;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	++*pos;
+	return c_start(m, pos);
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+}
+
 static const struct file_operations proc_tty_drivers_operations = {
 	.open		= tty_drivers_open,
 	.read		= seq_read,
@@ -136,6 +169,25 @@
 	.release	= seq_release,
 };
 
+static const struct seq_operations tty_console_op = {
+	.start		= c_start,
+	.next		= c_next,
+	.stop		= c_stop,
+	.show		= show_tty_console
+};
+
+static int tty_console_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &tty_console_op);
+}
+
+static const struct file_operations proc_tty_console_operations = {
+	.open		= tty_console_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release
+};
+
 /*
  * This is the handler for /proc/tty/ldiscs
  */
@@ -230,4 +282,7 @@
 	entry = create_proc_entry("tty/drivers", 0, NULL);
 	if (entry)
 		entry->proc_fops = &proc_tty_drivers_operations;
+	entry = create_proc_entry("tty/console", 0, NULL);
+	if (entry)
+		entry->proc_fops = &proc_tty_console_operations;
 }

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Randy Dunlap]

On Wed, 27 Feb 2008 13:18:57 -0500 Bill Nottingham wrote:

> I'm not seriously proposing this. But, as far as I can tell, this
> information isn't exposed to userspace anywhere, and it's a useful
> thing to know. I'm certainly open for better ideas on how to expose
> this (sysfs attributes? other?)
> 
> ....
> 
> The attached patch adds /proc/tty/console. The contents of it are
> simply a description of the current drivers attached to /dev/console.
> For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> yield:
> 
> # cat /proc/tty/console
> unknown             /dev/tty0
> serial              /dev/ttyS3
> 

So it omits other consoles (non-tty) intentionally?
or does it include them even though the procfs filename contains "tty"?

Anyway, I'd like to see something like this.
Compare http://www.xenotime.net/linux/patches/consoles-list.patch
(April-2006).


> 
> ---
> diff -ru linux-2.6.24.noarch/fs/proc/proc_tty.c linux/fs/proc/proc_tty.c
> --- linux-2.6.24.noarch/fs/proc/proc_tty.c	2008-02-27 12:50:59.000000000 -0500
> +++ linux/fs/proc/proc_tty.c	2008-02-27 12:25:54.000000000 -0500
> @@ -6,6 +6,7 @@
>  
>  #include <asm/uaccess.h>
>  
> +#include <linux/console.h>
>  #include <linux/init.h>
>  #include <linux/errno.h>
>  #include <linux/time.h>
> @@ -129,6 +130,38 @@
>  	return seq_open(file, &tty_drivers_op);
>  }
>  
> +static int show_tty_console(struct seq_file *m, void *v)
> +{
> +	int index;
> +	struct console *c;
> +
> +	for (c = console_drivers; c ; c = c->next) {
> +		struct tty_driver *t = NULL;
> +		if (!c->device)
> +			continue;
> +		t = c->device(c, &index);
> +		seq_printf(m, "%-20s", t->driver_name ? t->driver_name : "unknown");
> +		seq_printf(m, "/dev/%s%d", t->name, c->index);
> +		seq_printf(m, "\n");
> +	}
> +	return 0;
> +}
> +
> +static void *c_start(struct seq_file *m, loff_t *pos)
> +{
> +	return *pos == 0 ? &c_start : NULL;
> +}
> +
> +static void *c_next(struct seq_file *m, void *v, loff_t *pos)
> +{
> +	++*pos;
> +	return c_start(m, pos);
> +}
> +
> +static void c_stop(struct seq_file *m, void *v)
> +{
> +}
> +
>  static const struct file_operations proc_tty_drivers_operations = {
>  	.open		= tty_drivers_open,
>  	.read		= seq_read,
> @@ -136,6 +169,25 @@
>  	.release	= seq_release,
>  };
>  
> +static const struct seq_operations tty_console_op = {
> +	.start		= c_start,
> +	.next		= c_next,
> +	.stop		= c_stop,
> +	.show		= show_tty_console
> +};
> +
> +static int tty_console_open(struct inode *inode, struct file *file)
> +{
> +	return seq_open(file, &tty_console_op);
> +}
> +
> +static const struct file_operations proc_tty_console_operations = {
> +	.open		= tty_console_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= seq_release
> +};
> +
>  /*
>   * This is the handler for /proc/tty/ldiscs
>   */
> @@ -230,4 +282,7 @@
>  	entry = create_proc_entry("tty/drivers", 0, NULL);
>  	if (entry)
>  		entry->proc_fops = &proc_tty_drivers_operations;
> +	entry = create_proc_entry("tty/console", 0, NULL);
> +	if (entry)
> +		entry->proc_fops = &proc_tty_console_operations;
>  }

---
~Randy

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Bill Nottingham]

Randy Dunlap (randy.dunlap@oracle.com) said: 
> > I'm not seriously proposing this. But, as far as I can tell, this
> > information isn't exposed to userspace anywhere, and it's a useful
> > thing to know. I'm certainly open for better ideas on how to expose
> > this (sysfs attributes? other?)
> > 
> > ....
> > 
> > The attached patch adds /proc/tty/console. The contents of it are
> > simply a description of the current drivers attached to /dev/console.
> > For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> > yield:
> > 
> > # cat /proc/tty/console
> > unknown             /dev/tty0
> > serial              /dev/ttyS3
> > 
> 
> So it omits other consoles (non-tty) intentionally?
> or does it include them even though the procfs filename contains "tty"?

It only does consoles that have a tty_driver, as those are the ones I'd
find most interesting.

> Anyway, I'd like to see something like this.
> Compare http://www.xenotime.net/linux/patches/consoles-list.patch
> (April-2006).

Reading that, unless I'm missing something, you'd lose the device name
distinction (i.e., *which* serial port).

Bill

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Randy Dunlap]

On Wed, 27 Feb 2008 13:52:25 -0500 Bill Nottingham wrote:

> Randy Dunlap (randy.dunlap@oracle.com) said: 
> > > I'm not seriously proposing this. But, as far as I can tell, this
> > > information isn't exposed to userspace anywhere, and it's a useful
> > > thing to know. I'm certainly open for better ideas on how to expose
> > > this (sysfs attributes? other?)
> > > 
> > > ....
> > > 
> > > The attached patch adds /proc/tty/console. The contents of it are
> > > simply a description of the current drivers attached to /dev/console.
> > > For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> > > yield:
> > > 
> > > # cat /proc/tty/console
> > > unknown             /dev/tty0
> > > serial              /dev/ttyS3
> > > 
> > 
> > So it omits other consoles (non-tty) intentionally?
> > or does it include them even though the procfs filename contains "tty"?
> 
> It only does consoles that have a tty_driver, as those are the ones I'd
> find most interesting.
> 
> > Anyway, I'd like to see something like this.
> > Compare http://www.xenotime.net/linux/patches/consoles-list.patch
> > (April-2006).
> 
> Reading that, unless I'm missing something, you'd lose the device name
> distinction (i.e., *which* serial port).

I don't recall about that, but it would be Bad if correct.
I meant to list *all* consoles.  I'm interested in netconsole,
console=lp0, console=ttyUSB0, etc., as well as serial port consoles.

Thanks.
---
~Randy

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Andrew Morton]

On Wed, 27 Feb 2008 13:18:57 -0500 Bill Nottingham <notting@redhat.com> wrote:

> The attached patch adds /proc/tty/console. The contents of it are
> simply a description of the current drivers attached to /dev/console.
> For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> yield:
> 
> # cat /proc/tty/console
> unknown             /dev/tty0
> serial              /dev/ttyS3

I must say that the what-consoles-are-registered problem makes my head spin
sometimes too.  Seems a worthy objective.

However I think that a bunch of plain old printks which are emitted when a
console is added or removed would suffice?

We should display each console's CON_foo flags too.

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Bill Nottingham]

Andrew Morton (akpm@linux-foundation.org) said: 
> > The attached patch adds /proc/tty/console. The contents of it are
> > simply a description of the current drivers attached to /dev/console.
> > For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> > yield:
> > 
> > # cat /proc/tty/console
> > unknown             /dev/tty0
> > serial              /dev/ttyS3
> 
> I must say that the what-consoles-are-registered problem makes my head spin
> sometimes too.  Seems a worthy objective.
> 
> However I think that a bunch of plain old printks which are emitted when a
> console is added or removed would suffice?

We already do that in register_console(), albeit without flags.

My concern is I'd like to easily programmatically do something with this
info - ideally it would be in sysfs so it can easily be used from udev
or something similar.

Bill

Re: [PATCH, RFC, BAD IDEA] /proc/tty/console

[Andrew Morton]

On Fri, 29 Feb 2008 10:07:30 -0500
Bill Nottingham <notting@redhat.com> wrote:

> Andrew Morton (akpm@linux-foundation.org) said: 
> > > The attached patch adds /proc/tty/console. The contents of it are
> > > simply a description of the current drivers attached to /dev/console.
> > > For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
> > > yield:
> > > 
> > > # cat /proc/tty/console
> > > unknown             /dev/tty0
> > > serial              /dev/ttyS3
> > 
> > I must say that the what-consoles-are-registered problem makes my head spin
> > sometimes too.  Seems a worthy objective.
> > 
> > However I think that a bunch of plain old printks which are emitted when a
> > console is added or removed would suffice?
> 
> We already do that in register_console(), albeit without flags.

oh.

> My concern is I'd like to easily programmatically do something with this
> info - ideally it would be in sysfs so it can easily be used from udev
> or something similar.

That's the sort of information which really must be in the changelog, fully
spelled out.