[Devel] [PATCH 1/5] ve/tty: Provide interface for current tty inheritance

[Alexander Mikhalitsyn]

From: Cyrill Gorcunov <gorcunov at virtuozzo.com>

When fork() is called the current controlling terminal is inherited
by a child process. But in criu we fork all process first and then
restore their files, thus if terminal is opened in some children
its reference get lost. We refuse to checkpoint such configurations
at the moment in criu itself.

So to be able to restore this kind of container we need a way to
propagate controlling terminal to children processes, and here
is an interface "ve.ctty" entry on toplevel ve cgroup. One have
to pass pid of the donor task in first position followed by a series
of recipient pids.

https://jira.sw.ru/browse/PSBM-76490

CC: Andrey Vagin <avagin at virtuozzo.com>
CC: Andrey Ryabinin <aryabinin at virtuozzo.com>
CC: Konstantin Khorenko <khorenko at virtuozzo.com>
CC: "Denis V. Lunev" <den at virtuozzo.com>
Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>

khorenko@: we'll try to push the interface for ctty set up to mainstream.
May be it will be another interface like ioctl/netlink/etc, whatever.

This work (interface to mainstream) will be done in the scope of
https://jira.sw.ru/browse/PSBM-81687

(cherry picked from commit 098099f6daaf49d7fd06ea2aada56ead7958e8d1)

See also
451af50 ("cgroup: replace cftype->write_string() with cftype->write()")

VZ 8 rebase part https://jira.sw.ru/browse/PSBM-127797

Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
---
 kernel/ve/ve.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)

diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index 5bf187705f2a..db548c6d1c4b 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -25,6 +25,10 @@
 #include <linux/kthread.h>
 #include <linux/nsproxy.h>
 #include <linux/fs_struct.h>
+#include <linux/task_work.h>
+#include <linux/ctype.h>
+#include <linux/tty.h>
+
 #include <uapi/linux/vzcalluser.h>
 
 #include "../cgroup/cgroup-internal.h" /* For cgroup_task_count() */
@@ -1503,6 +1507,99 @@ static int ve_aio_max_nr_write(struct cgroup_subsys_state *css,
 }
 #endif
 
+static ssize_t ve_write_ctty(struct kernfs_open_file *of, char *buf,
+			 size_t nbytes, loff_t off)
+{
+	struct task_struct *tsk_from, *tsk_to;
+	struct tty_struct *tty_from, *tty_to;
+	pid_t pid_from, pid_to;
+	unsigned long flags;
+	char *pids;
+	int ret;
+
+	/*
+	 * Buffer format is the following
+	 *
+	 * 	pid_from pid_to pid_to ...
+	 *
+	 * where pid_to are pids to propagate
+	 * current terminal into.
+	 */
+
+	pids = skip_spaces(buf);
+	if (sscanf(pids, "%d", &pid_from) != 1)
+		return -EINVAL;
+	pids = strchr(pids, ' ');
+	if (!pids)
+		return -EINVAL;
+	pids = skip_spaces(pids);
+
+	rcu_read_lock();
+	tsk_from = find_task_by_vpid(pid_from);
+	if (tsk_from)
+		get_task_struct(tsk_from);
+	rcu_read_unlock();
+
+	if (!tsk_from)
+		return -ESRCH;
+
+	spin_lock_irqsave(&tsk_from->sighand->siglock, flags);
+	tty_from = tty_kref_get(tsk_from->signal->tty);
+	spin_unlock_irqrestore(&tsk_from->sighand->siglock, flags);
+
+	if (!tty_from) {
+		ret = -ENOTTY;
+		goto out;
+	}
+
+	ret = 0;
+	while (pids && *pids) {
+		if (sscanf(pids, "%d", &pid_to) != 1) {
+			ret = -EINVAL;
+			goto out;
+		}
+		pids = strchr(pids, ' ');
+		if (pids)
+			pids = skip_spaces(pids);
+
+		rcu_read_lock();
+		tsk_to = find_task_by_vpid(pid_to);
+		if (tsk_to)
+			get_task_struct(tsk_to);
+		rcu_read_unlock();
+
+		if (!tsk_to) {
+			ret = -ESRCH;
+			goto out;
+		}
+
+		if (tsk_from->task_ve == tsk_to->task_ve) {
+			spin_lock_irqsave(&tsk_to->sighand->siglock, flags);
+			tty_to = tsk_to->signal->tty;
+			if (!tty_to)
+				tsk_to->signal->tty = tty_kref_get(tty_from);
+			else
+				ret = -EBUSY;
+			spin_unlock_irqrestore(&tsk_to->sighand->siglock, flags);
+		} else
+			ret = -EINVAL;
+
+		put_task_struct(tsk_to);
+
+		if (ret)
+			goto out;
+	}
+
+out:
+	tty_kref_put(tty_from);
+	put_task_struct(tsk_from);
+
+	if (!ret)
+		ret = nbytes;
+
+	return ret;
+}
+
 static struct cftype ve_cftypes[] = {
 
 	{
@@ -1575,6 +1672,11 @@ static struct cftype ve_cftypes[] = {
 		.write_u64		= ve_aio_max_nr_write,
 	},
 #endif
+	{
+		.name			= "ctty",
+		.flags			= CFTYPE_ONLY_ON_ROOT,
+		.write			= ve_write_ctty,
+	},
 	{ }
 };
 
-- 
2.28.0