tty: Add a new file /proc/tty/consoles

Add a new file /proc/tty/consoles to be able to determine the registered
system console lines.  If the reading process holds /dev/console open at
the regular standard input stream the active device will be marked by an
asterisk.  Show possible operations and also decode the used flags of
the listed console lines.

Signed-off-by: Werner Fink <werner@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 158 insertions, 0 deletions

diff --git a/fs/proc/proc_tty.c b/fs/proc/proc_tty.c
index 83adcc869437..dc44f94022f1 100644
--- a/fs/proc/proc_tty.c
+++ b/fs/proc/proc_tty.c
@@ -12,7 +12,10 @@
 #include <linux/proc_fs.h>
 #include <linux/stat.h>
 #include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/console.h>
 #include <linux/seq_file.h>
+#include <linux/fdtable.h>
 #include <linux/bitops.h>
 
 /*
@@ -137,6 +140,160 @@ static const struct file_operations proc_tty_drivers_operations = {
 };
 
 /*
+ * The device ID of file descriptor 0 of the current reading
+ * task if a character device...
+ */
+static dev_t current_dev;
+
+/*
+ * This is the handler for /proc/tty/consoles
+ */
+static int show_console_dev(struct seq_file *m, void *v)
+{
+        const struct tty_driver *driver;
+        struct console *con;
+        int index, len;
+        char flags[10];
+        dev_t dev;
+
+        if (v == SEQ_START_TOKEN)
+                return 0;
+        con = (struct console *)v;
+        if (!con)
+                return 0;
+        driver = con->device(con, &index);
+        if (!driver)
+                return 0;
+        dev = MKDEV(driver->major, driver->minor_start) + index;
+
+        index = 0;
+        if (con->flags & CON_ENABLED)
+                flags[index++] = 'E';
+        if (con->flags & CON_CONSDEV)
+                flags[index++] = 'C';
+        if (con->flags & CON_BOOT)
+                flags[index++] = 'B';
+        if (con->flags & CON_PRINTBUFFER)
+                flags[index++] = 'p';
+        if (con->flags & CON_BRL)
+                flags[index++] = 'b';
+        if (con->flags & CON_ANYTIME)
+                flags[index++] = 'a';
+        if (current_dev == dev)
+                flags[index++] = '*';
+        flags[index] = 0;
+
+        seq_printf(m, "%s%d%n", con->name, con->index, &len);
+        len = 21 - len;
+        if (len < 1)
+                len = 1;
+        seq_printf(m, "%*c", len, ' ');
+        seq_printf(m, "%c%c%c (%s)%n", con->read ? 'R' : '-',
+                        con->write ? 'W' : '-', con->unblank ? 'U' : '-',
+                        flags, &len);
+        len = 13 - len;
+        if (len < 1)
+                len = 1;
+        seq_printf(m, "%*c%4d:%d\n", len, ' ', MAJOR(dev), MINOR(dev));
+
+        return 0;
+}
+
+/* iterator for consoles */
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+        struct console *con;
+        loff_t off = 0;
+
+        if (*pos == 0)
+                return SEQ_START_TOKEN;
+
+        acquire_console_sem();
+        for (con = console_drivers; con; con = con->next) {
+                if (!con->device)
+                        continue;
+                if (++off == *pos)
+                        break;
+        }
+        release_console_sem();
+
+        return con;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+        struct console *con;
+
+        acquire_console_sem();
+        if (v == SEQ_START_TOKEN)
+                con = console_drivers;
+        else
+                con = ((struct console *)v)->next;
+        for (; con; con = con->next) {
+                if (!con->device)
+                        continue;
+                ++*pos;
+                break;
+        }
+        release_console_sem();
+
+        return con;
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+}
+
+static const struct seq_operations tty_consoles_op = {
+        .start  = c_start,
+        .next   = c_next,
+        .stop   = c_stop,
+        .show   = show_console_dev
+};
+
+/*
+ * Used for open /proc/tty/consoles. Before this detect
+ * the device ID of file descriptor 0 of the current
+ * reading task if a character device...
+ */
+static int tty_consoles_open(struct inode *inode, struct file *file)
+{
+        struct files_struct *curfiles;
+
+        current_dev = 0;
+        curfiles = get_files_struct(current);
+        if (curfiles) {
+                const struct file *curfp;
+                spin_lock(&curfiles->file_lock);
+                curfp = fcheck_files(curfiles, 0);
+                if (curfp && curfp->private_data) {
+                        const struct inode *inode;
+                        dget(curfp->f_dentry);
+                        inode = curfp->f_dentry->d_inode;
+                        if (S_ISCHR(inode->i_mode)) {
+                                struct tty_struct *tty;
+                                tty = (struct tty_struct *)curfp->private_data;
+                                if (tty && tty->magic == TTY_MAGIC) {
+                                        tty = tty_pair_get_tty(tty);
+                                        current_dev = tty_devnum(tty);
+                                }
+                        }
+                        dput(curfp->f_dentry);
+                }
+                spin_unlock(&curfiles->file_lock);
+                put_files_struct(curfiles);
+        }
+        return seq_open(file, &tty_consoles_op);
+}
+
+static const struct file_operations proc_tty_consoles_operations = {
+        .open           = tty_consoles_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = seq_release,
+};
+
+/*
  * This function is called by tty_register_driver() to handle
  * registering the driver's /proc handler into /proc/tty/driver/<foo>
  */
@@ -186,4 +343,5 @@ void __init proc_tty_init(void)
         proc_tty_driver = proc_mkdir_mode("tty/driver", S_IRUSR|S_IXUSR, NULL);
         proc_create("tty/ldiscs", 0, NULL, &tty_ldiscs_proc_fops);
         proc_create("tty/drivers", 0, NULL, &proc_tty_drivers_operations);
+        proc_create("tty/consoles", 0, NULL, &proc_tty_consoles_operations);
 }