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Subject[PATCH v18 74/80] c/r: support for controlling terminal and job control
Date
Add checkpoint/restart of controlling terminal: current->signal->tty.
This is only done for session leaders.

If the session leader belongs to the ancestor pid-ns, then checkpoint
skips this tty; On restart, it will not be restored, and whatever tty
is in place from parent pid-ns (at restart) will be inherited.

Chagnelog [v1]:
- Don't restore tty_old_pgrp it pgid is CKPT_PID_NULL
- Initialize pgrp to NULL in restore_signal

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
---
checkpoint/signal.c | 79 +++++++++++++++++++++++++++++++++++++++-
drivers/char/tty_io.c | 33 +++++++++++++----
include/linux/checkpoint.h | 1 +
include/linux/checkpoint_hdr.h | 6 +++
include/linux/tty.h | 5 +++
5 files changed, 115 insertions(+), 9 deletions(-)

diff --git a/checkpoint/signal.c b/checkpoint/signal.c
index 5ff0734..cd3956d 100644
--- a/checkpoint/signal.c
+++ b/checkpoint/signal.c
@@ -316,11 +316,12 @@ static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
struct ckpt_hdr_signal *h;
struct signal_struct *signal;
struct sigpending shared_pending;
+ struct tty_struct *tty = NULL;
struct rlimit *rlim;
struct timeval tval;
cputime_t cputime;
unsigned long flags;
- int i, ret;
+ int i, ret = 0;

h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_SIGNAL);
if (!h)
@@ -398,9 +399,34 @@ static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
cputime_to_timeval(signal->it_prof_incr, &tval);
h->it_prof_incr = timeval_to_ns(&tval);

+ /* tty */
+ if (signal->leader) {
+ h->tty_old_pgrp = ckpt_pid_nr(ctx, signal->tty_old_pgrp);
+ tty = tty_kref_get(signal->tty);
+ if (tty) {
+ /* irq is already disabled */
+ spin_lock(&tty->ctrl_lock);
+ h->tty_pgrp = ckpt_pid_nr(ctx, tty->pgrp);
+ spin_unlock(&tty->ctrl_lock);
+ tty_kref_put(tty);
+ }
+ }
+
unlock_task_sighand(t, &flags);

- ret = ckpt_write_obj(ctx, &h->h);
+ /*
+ * If the session is in an ancestor namespace, skip this tty
+ * and set tty_objref = 0. It will not be explicitly restored,
+ * but rather inherited from parent pid-ns at restart time.
+ */
+ if (tty && ckpt_pid_nr(ctx, tty->session) > 0) {
+ h->tty_objref = checkpoint_obj(ctx, tty, CKPT_OBJ_TTY);
+ if (h->tty_objref < 0)
+ ret = h->tty_objref;
+ }
+
+ if (!ret)
+ ret = ckpt_write_obj(ctx, &h->h);
if (!ret)
ret = checkpoint_sigpending(ctx, &shared_pending);

@@ -471,8 +497,10 @@ static int restore_signal(struct ckpt_ctx *ctx)
struct ckpt_hdr_signal *h;
struct sigpending new_pending;
struct sigpending *pending;
+ struct tty_struct *tty = NULL;
struct itimerval itimer;
struct rlimit rlim;
+ struct pid *pgrp = NULL;
int i, ret;

h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_SIGNAL);
@@ -492,6 +520,40 @@ static int restore_signal(struct ckpt_ctx *ctx)
if (ret < 0)
goto out;

+ /* tty - session */
+ if (h->tty_objref) {
+ tty = ckpt_obj_fetch(ctx, h->tty_objref, CKPT_OBJ_TTY);
+ if (IS_ERR(tty)) {
+ ret = PTR_ERR(tty);
+ goto out;
+ }
+ /* this will fail unless we're the session leader */
+ ret = tiocsctty(tty, 0);
+ if (ret < 0)
+ goto out;
+ /* now restore the foreground group (job control) */
+ if (h->tty_pgrp) {
+ /*
+ * If tty_pgrp == CKPT_PID_NULL, below will
+ * fail, so no need for explicit test
+ */
+ ret = do_tiocspgrp(tty, tty_pair_get_tty(tty),
+ h->tty_pgrp);
+ if (ret < 0)
+ goto out;
+ }
+ } else {
+ /*
+ * If tty_objref isn't set, we _keep_ whatever tty we
+ * already have as a ctty. Why does this make sense ?
+ * - If our session is "within" the restart context,
+ * then that session has no controlling terminal.
+ * - If out session is "outside" the restart context,
+ * then we're like to keep whatever we inherit from
+ * the parent pid-ns.
+ */
+ }
+
/*
* Reset real/virt/prof itimer (in case they were set), to
* prevent unwanted signals after flushing current signals
@@ -503,7 +565,20 @@ static int restore_signal(struct ckpt_ctx *ctx)
do_setitimer(ITIMER_VIRTUAL, &itimer, NULL);
do_setitimer(ITIMER_PROF, &itimer, NULL);

+ /* tty - tty_old_pgrp */
+ if (current->signal->leader && h->tty_old_pgrp != CKPT_PID_NULL) {
+ rcu_read_lock();
+ pgrp = get_pid(_ckpt_find_pgrp(ctx, h->tty_old_pgrp));
+ rcu_read_unlock();
+ if (!pgrp)
+ goto out;
+ }
+
spin_lock_irq(&current->sighand->siglock);
+ /* tty - tty_old_pgrp */
+ put_pid(current->signal->tty_old_pgrp);
+ current->signal->tty_old_pgrp = pgrp;
+ /* pending signals */
pending = &current->signal->shared_pending;
flush_sigqueue(pending);
pending->signal = new_pending.signal;
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 72f4432..1b220c1 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2130,7 +2130,7 @@ static int fionbio(struct file *file, int __user *p)
* Takes ->siglock() when updating signal->tty
*/

-static int tiocsctty(struct tty_struct *tty, int arg)
+int tiocsctty(struct tty_struct *tty, int arg)
{
int ret = 0;
if (current->signal->leader && (task_session(current) == tty->session))
@@ -2219,10 +2219,10 @@ static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
}

/**
- * tiocspgrp - attempt to set process group
+ * do_tiocspgrp - attempt to set process group
* @tty: tty passed by user
* @real_tty: tty side device matching tty passed by user
- * @p: pid pointer
+ * @pid: pgrp_nr
*
* Set the process group of the tty to the session passed. Only
* permitted where the tty session is our session.
@@ -2230,10 +2230,10 @@ static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
* Locking: RCU, ctrl lock
*/

-static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
+int do_tiocspgrp(struct tty_struct *tty,
+ struct tty_struct *real_tty, pid_t pgrp_nr)
{
struct pid *pgrp;
- pid_t pgrp_nr;
int retval = tty_check_change(real_tty);
unsigned long flags;

@@ -2245,8 +2245,6 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
(current->signal->tty != real_tty) ||
(real_tty->session != task_session(current)))
return -ENOTTY;
- if (get_user(pgrp_nr, p))
- return -EFAULT;
if (pgrp_nr < 0)
return -EINVAL;
rcu_read_lock();
@@ -2268,6 +2266,27 @@ out_unlock:
}

/**
+ * tiocspgrp - attempt to set process group
+ * @tty: tty passed by user
+ * @real_tty: tty side device matching tty passed by user
+ * @p: pid pointer
+ *
+ * Set the process group of the tty to the session passed. Only
+ * permitted where the tty session is our session.
+ *
+ * Locking: RCU, ctrl lock
+ */
+
+static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
+{
+ pid_t pgrp_nr;
+
+ if (get_user(pgrp_nr, p))
+ return -EFAULT;
+ return do_tiocspgrp(tty, real_tty, pgrp_nr);
+}
+
+/**
* tiocgsid - get session id
* @tty: tty passed by user
* @real_tty: tty side of the tty pased by the user if a pty else the tty
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 8e1cce7..e00dd70 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -84,6 +84,7 @@ extern char *ckpt_fill_fname(struct path *path, struct path *root,

/* pids */
extern pid_t ckpt_pid_nr(struct ckpt_ctx *ctx, struct pid *pid);
+extern struct pid *_ckpt_find_pgrp(struct ckpt_ctx *ctx, pid_t pgid);

/* socket functions */
extern int ckpt_sock_getnames(struct ckpt_ctx *ctx,
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 842177f..9ae35a0 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -578,13 +578,19 @@ struct ckpt_rlimit {

struct ckpt_hdr_signal {
struct ckpt_hdr h;
+ /* rlimit */
struct ckpt_rlimit rlim[CKPT_RLIM_NLIMITS];
+ /* itimer */
__u64 it_real_value;
__u64 it_real_incr;
__u64 it_virt_value;
__u64 it_virt_incr;
__u64 it_prof_value;
__u64 it_prof_incr;
+ /* tty */
+ __s32 tty_objref;
+ __s32 tty_pgrp;
+ __s32 tty_old_pgrp;
} __attribute__((aligned(8)));

struct ckpt_hdr_signal_task {
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 295447b..9447251 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -471,6 +471,11 @@ extern void tty_ldisc_enable(struct tty_struct *tty);
/* This one is for ptmx_close() */
extern int tty_release(struct inode *inode, struct file *filp);

+/* These are for checkpoint/restart */
+extern int tiocsctty(struct tty_struct *tty, int arg);
+extern int do_tiocspgrp(struct tty_struct *tty,
+ struct tty_struct *real_tty, pid_t pgrp_nr);
+
#ifdef CONFIG_CHECKPOINT
struct ckpt_ctx;
struct ckpt_hdr_file;
--
1.6.0.4


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