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Subject[PATCH v2] pty: show associative slave of ptmx in fdinfo
Date
This patch adds "tty-index" field to /proc/PID/fdinfo/N if N
specifies /dev/ptmx. The field shows the index of associative
slave pts.

Though a minor number is given for each pts instance, ptmx is not.
It means there is no way in user-space to know the association between
file descriptors for pts/n and ptmx. (n = 0, 1, ...)

This is different from pipe. About pipe such association can be solved
by inode of pipefs.

Providing the way to know the association between pts/n and ptmx helps
users understand the status of running system. lsof can utilize this field.

Change in v2:

Remove all #ifdef CONFIG_PROC_FS/#endif.
Suggested by Greg KH.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
---
drivers/tty/pty.c | 8 +++++++-
drivers/tty/tty_io.c | 9 +++++++++
include/linux/tty_driver.h | 2 ++
3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index d1399aa..ce27be4 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -742,6 +742,11 @@ static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
}
}

+static void pty_show_fdinfo(struct tty_struct *tty, struct seq_file *m)
+{
+ seq_printf(m, "tty-index:\t%d\n", tty->index);
+}
+
static const struct tty_operations ptm_unix98_ops = {
.lookup = ptm_unix98_lookup,
.install = pty_unix98_install,
@@ -756,7 +761,8 @@ static const struct tty_operations ptm_unix98_ops = {
.ioctl = pty_unix98_ioctl,
.compat_ioctl = pty_unix98_compat_ioctl,
.resize = pty_resize,
- .cleanup = pty_cleanup
+ .cleanup = pty_cleanup,
+ .show_fdinfo = pty_show_fdinfo,
};

static const struct tty_operations pty_unix98_ops = {
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 974b13d..c3c8fd0 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -462,6 +462,14 @@ static int hung_up_tty_fasync(int fd, struct file *file, int on)
return -ENOTTY;
}

+static void tty_show_fdinfo(struct seq_file *m, struct file *file)
+{
+ struct tty_struct *tty = file_tty(file);
+
+ if (tty && tty->ops && tty->ops->show_fdinfo)
+ tty->ops->show_fdinfo(tty, m);
+}
+
static const struct file_operations tty_fops = {
.llseek = no_llseek,
.read = tty_read,
@@ -472,6 +480,7 @@ static const struct file_operations tty_fops = {
.open = tty_open,
.release = tty_release,
.fasync = tty_fasync,
+ .show_fdinfo = tty_show_fdinfo,
};

static const struct file_operations console_fops = {
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index b742b5e..570b05b 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -243,6 +243,7 @@
#include <linux/list.h>
#include <linux/cdev.h>
#include <linux/termios.h>
+#include <linux/seq_file.h>

struct tty_struct;
struct tty_driver;
@@ -285,6 +286,7 @@ struct tty_operations {
int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
int (*get_icount)(struct tty_struct *tty,
struct serial_icounter_struct *icount);
+ void (*show_fdinfo)(struct tty_struct *tty, struct seq_file *m);
#ifdef CONFIG_CONSOLE_POLL
int (*poll_init)(struct tty_driver *driver, int line, char *options);
int (*poll_get_char)(struct tty_driver *driver, int line);
--
2.9.4
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