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Message-Id: <1272723382-19470-77-git-send-email-orenl@cs.columbia.edu>
Date: Sat, 1 May 2010 10:15:58 -0400
From: Oren Laadan <orenl@...columbia.edu>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: containers@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, Serge Hallyn <serue@...ibm.com>,
Matt Helsley <matthltc@...ibm.com>,
Pavel Emelyanov <xemul@...nvz.org>,
Oren Laadan <orenl@...columbia.edu>,
Greg Kroah-Hartman <gregkh@...e.de>,
Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: [PATCH v21 076/100] c/r: [pty 1/2] allow allocation of desired pty slave
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).
Changelog[v19-rc3]:
- Rebase to kernel 2.6.33
Cc: Greg Kroah-Hartman <gregkh@...e.de>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
Signed-off-by: Oren Laadan <orenl@...columbia.edu>
Acked-by: Serge Hallyn <serue@...ibm.com>
Tested-by: Serge E. Hallyn <serue@...ibm.com>
---
drivers/char/pty.c | 66 +++++++++++++++++++++++++++++++++++++++++---
fs/devpts/inode.c | 13 +++++++--
include/linux/devpts_fs.h | 6 +++-
include/linux/tty.h | 1 -
4 files changed, 76 insertions(+), 10 deletions(-)
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index d83a431..cfe77c8 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -28,6 +28,7 @@
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
+#include <linux/file.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>
@@ -615,9 +616,10 @@ static const struct tty_operations pty_unix98_ops = {
};
/**
- * ptmx_open - open a unix 98 pty master
+ * __ptmx_open - open a unix 98 pty master
* @inode: inode of device file
* @filp: file pointer to tty
+ * @index: desired slave index
*
* Allocate a unix98 pty master device from the ptmx driver.
*
@@ -626,16 +628,15 @@ static const struct tty_operations pty_unix98_ops = {
* allocated_ptys_lock handles the list of free pty numbers
*/
-static int __ptmx_open(struct inode *inode, struct file *filp)
+static int __ptmx_open(struct inode *inode, struct file *filp, int index)
{
struct tty_struct *tty;
int retval;
- int index;
nonseekable_open(inode, filp);
/* find a device that is not in use. */
- index = devpts_new_index(inode);
+ index = devpts_new_index(inode, index);
if (index < 0)
return index;
@@ -671,12 +672,66 @@ static int ptmx_open(struct inode *inode, struct file *filp)
{
int ret;
+#ifdef CONFIG_CHECKPOINT
+ /*
+ * If current task is restarting, we skip the actual open.
+ * Instead, leave it up to the caller (restart code) to invoke
+ * __ptmx_open() with the desired pty index request.
+ *
+ * NOTE: this gives a half-baked file that has ptmx f_op but
+ * the tty (private_data) is NULL. It is the responsibility of
+ * the _caller_ to ensure proper initialization before
+ * allowing it to be used (ptmx_release() tolerates NULL tty).
+ */
+ if (current->flags & PF_RESTARTING)
+ return 0;
+#endif
+
lock_kernel();
- ret = __ptmx_open(inode, filp);
+ ret = __ptmx_open(inode, filp, UNSPECIFIED_PTY_INDEX);
unlock_kernel();
return ret;
}
+static int ptmx_release(struct inode *inode, struct file *filp)
+{
+#ifdef CONFIG_CHECKPOINT
+ /*
+ * It is possible for a restart to create a half-baked
+ * ptmx file - see ptmx_open(). In that case there is no
+ * tty (private_data) and nothing to do.
+ */
+ if (!filp->private_data)
+ return 0;
+#endif
+
+ return tty_release(inode, filp);
+}
+
+struct file *pty_open_by_index(char *ptmxpath, int index)
+{
+ struct file *ptmxfile;
+ int ret;
+
+ /*
+ * We need to pick a way to specify which devpts mountpoint to
+ * use. For now, we'll just use whatever /dev/ptmx points to.
+ */
+ ptmxfile = filp_open(ptmxpath, O_RDWR|O_NOCTTY, 0);
+ if (IS_ERR(ptmxfile))
+ return ptmxfile;
+
+ lock_kernel();
+ ret = __ptmx_open(ptmxfile->f_dentry->d_inode, ptmxfile, index);
+ unlock_kernel();
+ if (ret) {
+ fput(ptmxfile);
+ return ERR_PTR(ret);
+ }
+
+ return ptmxfile;
+}
+
static struct file_operations ptmx_fops;
static void __init unix98_pty_init(void)
@@ -733,6 +788,7 @@ static void __init unix98_pty_init(void)
/* Now create the /dev/ptmx special device */
tty_default_fops(&ptmx_fops);
ptmx_fops.open = ptmx_open;
+ ptmx_fops.release = ptmx_release;
cdev_init(&ptmx_cdev, &ptmx_fops);
if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 0120247..75fb8c5 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -433,11 +433,11 @@ 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);
- int index;
+ int index = req_idx;
int ida_ret;
retry:
@@ -445,7 +445,9 @@ retry:
return -ENOMEM;
mutex_lock(&allocated_ptys_lock);
- ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
+ if (index == UNSPECIFIED_PTY_INDEX)
+ index = 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 +455,11 @@ retry:
return -EIO;
}
+ if (req_idx != UNSPECIFIED_PTY_INDEX && 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/devpts_fs.h b/include/linux/devpts_fs.h
index 5ce0e5f..163a70e 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -15,9 +15,13 @@
#include <linux/errno.h>
+#define UNSPECIFIED_PTY_INDEX -1
+
#ifdef CONFIG_UNIX98_PTYS
-int devpts_new_index(struct inode *ptmx_inode);
+struct file *pty_open_by_index(char *ptmxpath, int index);
+
+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/tty.h b/include/linux/tty.h
index 4409967..d0cbcec 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -513,7 +513,6 @@ extern void tty_ldisc_begin(void);
/* This last one is just for the tty layer internals and shouldn't be used elsewhere */
extern void tty_ldisc_enable(struct tty_struct *tty);
-
/* n_tty.c */
extern struct tty_ldisc_ops tty_ldisc_N_TTY;
extern void n_tty_inherit_ops(struct tty_ldisc_ops *ops);
--
1.6.3.3
--
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