TIOCGDEV ioctl

PATCH Kurt Garloff 7 participants 12 messages Dec 16, 2000 – Dec 21, 2000

Subsystems (2)

Char and misc drivers Proc filesystem

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Kurt Garloff

author

2000-12-16 01:29 UTC #0 lore raw

Hi Linus, Alan,

some applications do need to know where the console (/dev/console) actually maps to. For processes with a controlling terminal, you may see it in /proc/$$/stat. However, daemons are supposed to run detached (they don't want to get killed by ^C) and some processes like init or bootlogd do still need to be able to find out.

The kernel provides this information -- sort of:
It contains the TIOCTTYGSTRUCT syscall which returns a struct. Of course, it changes between different kernel archs and revisions, so using it is an ugly hack. Grab for TIOCTTYGSTRUCT_HACK in the bootlogd.c file of the sysvinit sources. Shudder!

Having a new ioctl, just returning the device no is a much cleaner solution, IMHO. So, I created the TIOCGDEV, which Miquel suggests in his sysvinit sources. It makes querying the actual console device as easy as int tty; ioctl (0, TIOCGDEV, &tty);

Patches against 2.2.18 and 2.4.0-testX are attached. Please apply.

Signature · 3 lines

Kurt Garloff  <[email protected]>                          Eindhoven, NL
GPG key: See mail header, key servers         Linux kernel development
SuSE GmbH, Nuernberg, FRG                               SCSI, Security

drivers/char/tty_io.c +2 -1

diff -uNr linux-2.4.0_test10.SuSE/drivers/char/tty_io.c linux-2.4.0_test10.TIOCGDEV/drivers/char/tty_io.c
@@ -1766,7 +1766,8 @@
 #endif
 		case TIOCTTYGSTRUCT:
 			return tiocttygstruct(tty, (struct tty_struct *) arg);
-
+		case TIOCGDEV:
+			return put_user (kdev_to_nr (real_tty->device, (unsigned int*) arg);
 		/*
 		 * Break handling
 		 */

include/asm/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-alpha/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-alpha/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-alpha/ioctls.h
@@ -91,6 +91,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454

include/asm-arm/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-arm/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-arm/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-i386/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-i386/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-i386/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-ia64/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-ia64/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-ia64/ioctls.h
@@ -54,6 +54,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-m68k/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-m68k/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-m68k/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-mips/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-mips/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-mips/ioctls.h
@@ -100,6 +100,7 @@
 #define TIOCGSID	0x7416  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5488
 #define TIOCSERGWILD	0x5489

include/asm-mips64/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-mips64/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-mips64/ioctls.h
@@ -100,6 +100,7 @@
 #define TIOCGSID	0x7416  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5488
 #define TIOCSERGWILD	0x5489

include/asm-ppc/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-ppc/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-ppc/ioctls.h
@@ -88,6 +88,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454

include/asm-s390/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-s390/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-s390/ioctls.h
@@ -57,6 +57,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-sh/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-sh/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-sh/ioctls.h
@@ -80,6 +80,7 @@
 #define TIOCGSID	_IOR('T', 41, pid_t) /* 0x5429 */ /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	_IO('T', 83) /* 0x5453 */
 #define TIOCSERGWILD	_IOR('T', 84,  int) /* 0x5454 */

include/asm-sparc/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-sparc/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-sparc/ioctls.h
@@ -99,6 +99,7 @@
 #define TIOCSSERIAL	0x541F
 #define TCSBRKP		0x5425
 #define TIOCTTYGSTRUCT	0x5426
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454
 #define TIOCSERSWILD	0x5455

include/asm-sparc64/ioctls.h +1 -0

diff -uNr linux-2.4.0_test10.SuSE/include/asm-sparc64/ioctls.h linux-2.4.0_test10.TIOCGDEV/include/asm-sparc64/ioctls.h
@@ -100,6 +100,7 @@
 #define TIOCSSERIAL	0x541F
 #define TCSBRKP		0x5425
 #define TIOCTTYGSTRUCT	0x5426
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454
 #define TIOCSERSWILD	0x5455

drivers/char/tty_io.c +3 -0

diff -uNr linux-2.2.18.SuSE/drivers/char/tty_io.c linux-2.2.18.TIOCGDEV/drivers/char/tty_io.c
@@ -1768,6 +1768,9 @@
 		case TIOCTTYGSTRUCT:
 			return tiocttygstruct(tty, (struct tty_struct *) arg);
 
+		case TIOCGDEV:
+			return put_user (kdev_t_to_nr (real_tty->device), (unsigned int *) arg);
+		
 		/*
 		 * Break handling
 		 */

include/asm-alpha/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-alpha/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-alpha/ioctls.h
@@ -88,6 +88,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454

include/asm-arm/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-arm/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-arm/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-i386/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-i386/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-i386/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-m68k/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-m68k/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-m68k/ioctls.h
@@ -49,6 +49,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-mips/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-mips/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-mips/ioctls.h
@@ -100,6 +100,7 @@
 #define TIOCGSID	0x7416  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5488
 #define TIOCSERGWILD	0x5489

include/asm-ppc/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-ppc/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-ppc/ioctls.h
@@ -88,6 +88,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454

include/asm-s390/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-s390/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-s390/ioctls.h
@@ -57,6 +57,7 @@
 #define TIOCGSID	0x5429  /* Return the session ID of FD */
 #define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 
 #define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
 #define FIOCLEX		0x5451

include/asm-sparc/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-sparc/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-sparc/ioctls.h
@@ -99,6 +99,7 @@
 #define TIOCSSERIAL	0x541F
 #define TCSBRKP		0x5425
 #define TIOCTTYGSTRUCT	0x5426
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454
 #define TIOCSERSWILD	0x5455

include/asm-sparc64/ioctls.h +1 -0

diff -uNr linux-2.2.18.SuSE/include/asm-sparc64/ioctls.h linux-2.2.18.TIOCGDEV/include/asm-sparc64/ioctls.h
@@ -100,6 +100,7 @@
 #define TIOCSSERIAL	0x541F
 #define TCSBRKP		0x5425
 #define TIOCTTYGSTRUCT	0x5426
+#define TIOCGDEV	_IOR('T',0x32, unsigned int) /* Get real dev no below /dev/console */
 #define TIOCSERCONFIG	0x5453
 #define TIOCSERGWILD	0x5454
 #define TIOCSERSWILD	0x5455

Linus Torvalds

2000-12-16 01:42 UTC #1 lore raw

Quoted 6 lines · Kurt Garloff

The kernel provides this information -- sort of:
It contains the TIOCTTYGSTRUCT syscall which returns a struct. Of course, it changes between different kernel archs and revisions, so using it is an ugly hack. Grab for TIOCTTYGSTRUCT_HACK in the bootlogd.c file of the sysvinit sources. Shudder!

Please instead do the same thing /dev/tty does, namely a sane interface that shows it as a symlink in /proc (or even in /dev)

Linus

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Alexander Viro

2000-12-16 02:24 UTC #2 lore raw

Quoted 2 lines · Linus Torvalds

Please instead do the same thing /dev/tty does, namely a sane interface that shows it as a symlink in /proc (or even in /dev)

There you go... (/proc/tty/console -> /dev/tty<current_VC>; may very well be dangling, but then you have a current VC even if your /dev consists of /dev/console and nothing else, so there's nothing to do about that; doesn't handle TIOCCONS redirects, but IMO that should be a separate object anyway).
Cheers,
Al

fs/proc/proc_tty.c +23 -0

diff -urN rc12-pre8/fs/proc/proc_tty.c rc12-pre8-tty/fs/proc/proc_tty.c
@@ -166,6 +166,26 @@
 	driver->proc_entry = 0;
 }
 
+extern int fg_console;
+static int proc_cons_readlink(struct dentry *dentry, char *buffer, int buflen)
+{
+	char tmp[30];
+	sprintf(tmp, "/dev/tty%d", fg_console);
+	return vfs_readlink(dentry,buffer,buflen,tmp);
+}
+
+static int proc_cons_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+	char tmp[30];
+	sprintf(tmp, "/dev/tty%d", fg_console);
+	return vfs_follow_link(nd,tmp);
+}	
+
+static struct inode_operations proc_cons_operations = {
+	readlink:	proc_cons_readlink,
+	follow_link:	proc_cons_follow_link,
+};
+
 /*
  * Called by proc_root_init() to initialize the /proc/tty subtree
  */

@@ -175,6 +195,9 @@
 		return;
 	proc_tty_ldisc = proc_mkdir("tty/ldisc", 0);
 	proc_tty_driver = proc_mkdir("tty/driver", 0);
+
+	proc_tty_console = create_proc_entry("tty/console", S_IFLNK|0777, NULL);
+	proc_tty_console->proc_iops = &proc_console_ops;
 
 	create_proc_read_entry("tty/ldiscs", 0, 0, tty_ldiscs_read_proc,NULL);
 	create_proc_read_entry("tty/drivers", 0, 0, tty_drivers_read_proc,NULL);

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Miquel van Smoorenburg

2000-12-16 11:17 UTC #3 lore raw

In reply to Linus Torvalds

According to Alexander Viro:

Quoted 6 lines · Linus Torvalds

Quoted 3 lines
Please instead do the same thing /dev/tty does, namely a sane interface that shows it as a symlink in /proc (or even in /dev)
There you go... (/proc/tty/console -> /dev/tty<current_VC>; may very well

The current VT (fg_console) and /dev/console are 2 different things ... /dev/console might be /dev/ttyS1. Besides to get at fg_console we already have ioctl(/dev/tty0, TIOCLINUX, 12)

There is currently no way to find out with what device /dev/console is associated.

Why is that needed? For example, I wrote a program 'bootlogd' that opens /dev/console and a pty pair, uses TIOCCONS to redirect console messages to the pty pair so they can be logged. However one would like to write those messages to the _actual_ console as well, but there is no way to find out what the real console is.

For this application a ioctl is better than a /proc symlink since it would be started before /proc is even mounted.

Mike.

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Alexander Viro

2000-12-16 11:46 UTC #4 lore raw

Quoted 11 lines · Miquel van Smoorenburg

There is currently no way to find out with what device /dev/console is associated.
Why is that needed? For example, I wrote a program 'bootlogd' that opens /dev/console and a pty pair, uses TIOCCONS to redirect console messages to the pty pair so they can be logged. However one would like to write those messages to the _actual_ console as well, but there is no way to find out what the real console is.
For this application a ioctl is better than a /proc symlink since it would be started before /proc is even mounted.

So mount it... It's not like you didn't have enough privileges for that, after all, and mount("proc", "/proc", "proc", 0, 0); doesn't look too complex.

OK, I can see the point of finding out where the console is redirected to. How about the following:

	/proc/sys/vc -> /dev/tty<n>
	/proc/sys/console -> where the hell did we redirect it or
			     vc if there's no redirect right now

Will that be OK with you?

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Miquel van Smoorenburg

2000-12-16 12:11 UTC #5 lore raw

In reply to Miquel van Smoorenburg

According to Alexander Viro:

Quoted 7 lines

OK, I can see the point of finding out where the console is redirected to. How about the following:
	/proc/sys/vc -> /dev/tty<n>
	/proc/sys/console -> where the hell did we redirect it or
			     vc if there's no redirect right now
Will that be OK with you?

Well, I'd prefer the ioctl, but I can see the general direction the kernel is heading to: get rid of numeric ioctls and sysctl()s and put all that info under /proc.

However /proc/sys only contains directories now, it would look kindof ugly to put 2 symlinks in there directly. Oh well.

Mike.

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Alexander Viro

2000-12-16 12:28 UTC #6 lore raw

Quoted 9 lines · Miquel van Smoorenburg

According to Alexander Viro:
Quoted 7 lines
OK, I can see the point of finding out where the console is redirected to. How about the following:
	/proc/sys/vc -> /dev/tty<n>
	/proc/sys/console -> where the hell did we redirect it or
			     vc if there's no redirect right now
Will that be OK with you?

Quoted 5 lines

Well, I'd prefer the ioctl, but I can see the general direction the kernel is heading to: get rid of numeric ioctls and sysctl()s and put all that info under /proc.
However /proc/sys only contains directories now, it would look

Huh? Oh, sorry. /proc/tty, indeed - it was a braino. BTW, I think that a mini-fs with a device node for each registered console + symlink (say it, "default") pointing to the default one might make sense too. Comments?

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Kurt Garloff

author

2000-12-19 12:07 UTC #7 lore raw

In reply to Miquel van Smoorenburg

Quoted 5 lines · Alexander Viro

Quoted 4 lines · Miquel van Smoorenburg
According to Alexander Viro:
Quoted 3 lines
OK, I can see the point of finding out where the console is redirected to. How about the following:

Quoted 8 lines

Quoted 8 lines
Quoted 4 lines
	/proc/sys/vc -> /dev/tty<n>
	/proc/sys/console -> where the hell did we redirect it or
			     vc if there's no redirect right now
Will that be OK with you?
Well, I'd prefer the ioctl, but I can see the general direction the kernel is heading to: get rid of numeric ioctls and sysctl()s and put all that info under /proc.

Yes; it looks nicer not to grow the number of ioctls more and more, but to make things more visible in /proc.

On the other hand, there are some advantages of the ioctl:
It's fast, easy and does not need /proc. That cab be of relevance for embedded devices, e.g., where ram is short.

Quoted 4 lines

Huh? Oh, sorry. /proc/tty, indeed - it was a braino. BTW, I think that a mini-fs with a device node for each registered console + symlink (say it, "default") pointing to the default one might make sense too. Comments?

Yes, looks like a good solution to me.
But that's far more complicated than the ioctl.

Looking at the sources and starting to write some code, it's not so obvious to me how to get the right device no all the time and how to create the correct symlink also in 2.2. Yes, it needs to work on both 2.2 and 2.4 kernels.

So, I'd like to ask for inclusion of the original patch.
Or can we come up with the /proc/tty solution without adding too much code?

Regards,

Signature · 3 lines

Kurt Garloff  <[email protected]>                          Eindhoven, NL
GPG key: See mail header, key servers         Linux kernel development
SuSE GmbH, Nuernberg, FRG                               SCSI, Security

James Simmons

2000-12-16 01:49 UTC #8 lore raw

In reply to Kurt Garloff

Quoted 15 lines

Hi Linus, Alan,
some applications do need to know where the console (/dev/console) actually maps to. For processes with a controlling terminal, you may see it in /proc/$$/stat. However, daemons are supposed to run detached (they don't want to get killed by ^C) and some processes like init or bootlogd do still need to be able to find out.
The kernel provides this information -- sort of:
It contains the TIOCTTYGSTRUCT syscall which returns a struct. Of course, it changes between different kernel archs and revisions, so using it is an ugly hack. Grab for TIOCTTYGSTRUCT_HACK in the bootlogd.c file of the sysvinit sources. Shudder!

Quoted 7 lines

Having a new ioctl, just returning the device no is a much cleaner solution, IMHO. So, I created the TIOCGDEV, which Miquel suggests in his sysvinit sources. It makes querying the actual console device as easy as int tty; ioctl (0, TIOCGDEV, &tty);
Patches against 2.2.18 and 2.4.0-testX are attached. Please apply.

Based on fgconsole.c. I just threw it together in a few minutes.

/*
* consolewhat.c - Prints which VC /dev/console is. */
#include <sys/ioctl.h>
#include <linux/vt.h>

int

main(){
    struct vt_stat vtstat;
    int fd;	

    fd = open("/dev/console", O_RDONLY);	

    if (fd < 0 && errno == EACCES)
	fd = open("/dev/console", O_WRONLY);
    if (fd < 0)
	return -1;

    if (ioctl(fd, VT_GETSTATE, &vtstat)) {
        perror("consolewhat: VT_GETSTATE");
	exit(1);
    }
    printf("%d\n", vtstat.v_active);
    return 0;
}

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Miquel van Smoorenburg

2000-12-16 11:24 UTC #9 lore raw

In reply to Kurt Garloff

In article <[email protected]>,

Quoted 4 lines · James Simmons

Based on fgconsole.c. I just threw it together in a few minutes. /*
* consolewhat.c - Prints which VC /dev/console is.
*/

You're confusing /dev/console and /dev/tty0. /dev/console might be associated with /dev/ttyS0 or /dev/lp1

Mike.

Signature · 5 lines

RAND USR 16514
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James Simmons

2000-12-18 17:38 UTC #10 lore raw

Quoted 3 lines

You're confusing /dev/console and /dev/tty0. /dev/console might be associated with /dev/ttyS0 or /dev/lp1

Oops. Forgot about serial consoles :-(

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Dr. Werner Fink

2000-12-21 14:53 UTC #11 lore raw

In reply to Kurt Garloff

Quoted 4 lines · Linus Torvalds

Quoted 1 line · Kurt Garloff

Quoted 8 lines

Quoted 5 lines
The kernel provides this information -- sort of:
It contains the TIOCTTYGSTRUCT syscall which returns a struct. Of course, it changes between different kernel archs and revisions, so using it is an ugly hack. Grab for TIOCTTYGSTRUCT_HACK in the bootlogd.c file of the sysvinit sources. Shudder!
Please instead do the same thing /dev/tty does, namely a sane interface that shows it as a symlink in /proc (or even in /dev)

Not a symlink but this is what is needed: if fd 0 of the current task is a tty then give the hash of the tty. I'm using fd 0 because current->tty may not be set for spawned tasks of init.

I've attached two patches, one for 2.4 and one for 2.2. They're rather simple, therefore one may use this for setting a link.

Werner

BTW: I'm missing a real replacement for my sys_revoke() patch done at the end of October. Al Viro has wipe it out but never shows an alternative way of implementing such a beast.

proc/proc_tty.c +30 -1

@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
+#include <linux/file.h>
 #include <linux/proc_fs.h>
 #include <linux/stat.h>
 #include <linux/tty.h>

@@ -22,6 +23,8 @@
 				 int count, int *eof, void *data);
 static int tty_ldiscs_read_proc(char *page, char **start, off_t off,
 				int count, int *eof, void *data);
+static int real_tty_read_proc(char *page, char **start, off_t off,
+				int count, int *eof, void *data);
 
 /*
  * The /proc/tty directory inodes...

@@ -128,7 +131,32 @@
 }
 
 /*
- * Thsi function is called by register_tty_driver() to handle
+ * This is the handler for /proc/tty/tty
+ */
+static int real_tty_read_proc(char *page, char **start, off_t off,
+				int count, int *eof, void *data)
+{
+	struct	file * zero = fcheck(0); /* of current task */
+	struct	tty_struct * tty = NULL;
+	unsigned int dev = 0;
+	int	len = 0;
+	off_t	begin = 0;
+
+	if (zero)
+		tty = (struct tty_struct *)zero->private_data;
+	if (tty && tty->magic == TTY_MAGIC)
+		dev = kdev_t_to_nr(tty->device);
+
+	len += sprintf(page+len, "%u\n", dev);
+
+	if (off >= len+begin)
+		return 0;
+	*start = page + (off-begin);
+	return ((count < begin+len-off) ? count : begin+len-off);
+}
+
+/*
+ * This function is called by register_tty_driver() to handle
  * registering the driver's /proc handler into /proc/tty/driver/<foo>
  */
 void proc_tty_register_driver(struct tty_driver *driver)

@@ -178,4 +206,5 @@
 
 	create_proc_read_entry("tty/ldiscs", 0, 0, tty_ldiscs_read_proc,NULL);
 	create_proc_read_entry("tty/drivers", 0, 0, tty_drivers_read_proc,NULL);
+	create_proc_read_entry("tty/tty", 0, 0, real_tty_read_proc,NULL);
 }

proc/proc_tty.c +32 -2

@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
+#include <linux/file.h>
 #include <linux/proc_fs.h>
 #include <linux/stat.h>
 #include <linux/tty.h>

@@ -22,6 +23,8 @@
 				 int count, int *eof, void *data);
 static int tty_ldiscs_read_proc(char *page, char **start, off_t off,
 				int count, int *eof, void *data);
+static int real_tty_read_proc(char *page, char **start, off_t off,
+				 int count, int *eof, void *data);
 
 /*
  * The /proc/tty directory inodes...

@@ -128,7 +131,32 @@
 }
 
 /*
- * Thsi function is called by register_tty_driver() to handle
+ * This is the handler for /proc/tty/tty
+ */
+static int real_tty_read_proc(char *page, char **start, off_t off,
+				 int count, int *eof, void *data)
+{
+	struct	file * zero = fcheck_task(current, 0);
+	struct	tty_struct * tty = NULL;
+	unsigned int dev = 0;
+	int	len = 0;
+	off_t	begin = 0;
+
+	if (zero)
+		tty = (struct tty_struct *)zero->private_data;
+	if (tty && tty->magic == TTY_MAGIC)
+		dev = kdev_t_to_nr(tty->device);
+
+	len += sprintf(page+len, "%u\n", dev);
+
+	if (off >= len+begin)
+		return 0;
+	*start = page + (off-begin);
+	return ((count < begin+len-off) ? count : begin+len-off);
+}
+
+/*
+ * This function is called by register_tty_driver() to handle
  * registering the driver's /proc handler into /proc/tty/driver/<foo>
  */
 void proc_tty_register_driver(struct tty_driver *driver)

@@ -185,5 +213,7 @@
 
 	ent = create_proc_entry("tty/drivers", 0, 0);
 	ent->read_proc = tty_drivers_read_proc;
-}
 
+	ent = create_proc_entry("tty/tty", 0, 0);
+	ent->read_proc = real_tty_read_proc;
+}