During restart, we need to allocate pty slaves with the same
identifiers as recorded during checkpoint. Modify the allocation code
to allow an in-kernel caller to request a specific slave identifier.
For this, add a new field to task_struct - 'required_id'. It will
hold the desired identifier when restoring a (master) pty.
The code in ptmx_open() will use this value only for tasks that try to
open /dev/ptmx that are restarting (PF_RESTARTING), and if the value
isn't CKPT_REQUIRED_NONE (-1).
Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
---
checkpoint/sys.c | 7 +++++++
drivers/char/pty.c | 9 +++++++--
fs/devpts/inode.c | 10 ++++++++--
include/linux/checkpoint.h | 2 ++
include/linux/devpts_fs.h | 2 +-
include/linux/sched.h | 1 +
6 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index 525182a..3db18f7 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -339,6 +339,13 @@ SYSCALL_DEFINE3(restart, pid_t, pid, int, fd, unsigned long, flags)
return ret;
}
+static int __init checkpoint_init(void)
+{
+ init_task.required_id = CKPT_REQUIRED_NONE;
+ return 0;
+}
+__initcall(checkpoint_init);
+
/* 'ckpt_debug_level' controls the verbosity level of c/r code */
#ifdef CONFIG_CHECKPOINT_DEBUG
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 6e6942c..326c2e9 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -633,12 +633,17 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
{
struct tty_struct *tty;
int retval;
- int index;
+ int index = 0;
nonseekable_open(inode, filp);
+#ifdef CONFIG_CHECKPOINT
+ /* when restarting, request specific index */
+ if (current->flags & PF_RESTARTING)
+ index = (int) current->required_id;
+#endif
/* find a device that is not in use. */
- index = devpts_new_index(inode);
+ index = devpts_new_index(inode, index);
if (index < 0)
return index;
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 75efb02..8921726 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -433,7 +433,7 @@ static struct file_system_type devpts_fs_type = {
* to the System V naming convention
*/
-int devpts_new_index(struct inode *ptmx_inode)
+int devpts_new_index(struct inode *ptmx_inode, int req_idx)
{
struct super_block *sb = pts_sb_from_inode(ptmx_inode);
struct pts_fs_info *fsi = DEVPTS_SB(sb);
@@ -445,7 +445,8 @@ retry:
return -ENOMEM;
mutex_lock(&allocated_ptys_lock);
- ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
+ index = (req_idx >= 0 ? req_idx : 0);
+ ida_ret = ida_get_new_above(&fsi->allocated_ptys, index, &index);
if (ida_ret < 0) {
mutex_unlock(&allocated_ptys_lock);
if (ida_ret == -EAGAIN)
@@ -453,6 +454,11 @@ retry:
return -EIO;
}
+ if (req_idx >= 0 && index != req_idx) {
+ ida_remove(&fsi->allocated_ptys, index);
+ mutex_unlock(&allocated_ptys_lock);
+ return -EBUSY;
+ }
if (index >= pty_limit) {
ida_remove(&fsi->allocated_ptys, index);
mutex_unlock(&allocated_ptys_lock);
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 1d050f8..473164e 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -46,6 +46,8 @@
#define CHECKPOINT_USER_FLAGS CHECKPOINT_SUBTREE
#define RESTART_USER_FLAGS (RESTART_TASKSELF | RESTART_FROZEN)
+#define CKPT_REQUIRED_NONE ((unsigned long) -1L)
+
extern void exit_checkpoint(struct task_struct *tsk);
extern int ckpt_kwrite(struct ckpt_ctx *ctx, void *buf, int count);
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 5ce0e5f..14948ee 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -17,7 +17,7 @@
#ifdef CONFIG_UNIX98_PTYS
-int devpts_new_index(struct inode *ptmx_inode);
+int devpts_new_index(struct inode *ptmx_inode, int req_idx);
void devpts_kill_index(struct inode *ptmx_inode, int idx);
/* mknod in devpts */
int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0e67de7..f6f1350 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1481,6 +1481,7 @@ struct task_struct {
#endif /* CONFIG_TRACING */
#ifdef CONFIG_CHECKPOINT
struct ckpt_ctx *checkpoint_ctx;
+ unsigned long required_id;
#endif
};
--
1.6.0.4
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