linux-kernel - [PATCH v2 10/10] tty: Refactor tty

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Message-Id: <1452402833-8652-11-git-send-email-peter@hurleysoftware.com>
Date:	Sat,  9 Jan 2016 21:13:53 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH v2 10/10] tty: Refactor tty_open()

Extract the driver lookup and reopen-or-initialize logic into helper
function tty_open_by_driver(). No functional change.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_io.c | 120 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 67 insertions(+), 53 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index d223e54..cef913c 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2001,6 +2001,69 @@ static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
 }
 
 /**
+ *	tty_open_by_driver	-	open a tty device
+ *	@device: dev_t of device to open
+ *	@inode: inode of device file
+ *	@filp: file pointer to tty
+ *
+ *	Performs the driver lookup, checks for a reopen, or otherwise
+ *	performs the first-time tty initialization.
+ *
+ *	Returns the locked initialized or re-opened &tty_struct
+ *
+ *	Claims the global tty_mutex to serialize:
+ *	  - concurrent first-time tty initialization
+ *	  - concurrent tty driver removal w/ lookup
+ *	  - concurrent tty removal from driver table
+ */
+static struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
+					     struct file *filp)
+{
+	struct tty_struct *tty;
+	struct tty_driver *driver = NULL;
+	int index = -1;
+	int retval;
+
+	mutex_lock(&tty_mutex);
+	driver = tty_lookup_driver(device, filp, &index);
+	if (IS_ERR(driver)) {
+		mutex_unlock(&tty_mutex);
+		return ERR_CAST(driver);
+	}
+
+	/* check whether we're reopening an existing tty */
+	tty = tty_driver_lookup_tty(driver, inode, index);
+	if (IS_ERR(tty)) {
+		mutex_unlock(&tty_mutex);
+		goto out;
+	}
+
+	if (tty) {
+		mutex_unlock(&tty_mutex);
+		retval = tty_lock_interruptible(tty);
+		if (retval) {
+			if (retval == -EINTR)
+				retval = -ERESTARTSYS;
+			tty = ERR_PTR(retval);
+			goto out;
+		}
+		/* safe to drop the kref from tty_driver_lookup_tty() */
+		tty_kref_put(tty);
+		retval = tty_reopen(tty);
+		if (retval < 0) {
+			tty_unlock(tty);
+			tty = ERR_PTR(retval);
+		}
+	} else { /* Returns with the tty_lock held for now */
+		tty = tty_init_dev(driver, index);
+		mutex_unlock(&tty_mutex);
+	}
+out:
+	tty_driver_kref_put(driver);
+	return tty;
+}
+
+/**
  *	tty_open		-	open a tty device
  *	@inode: inode of device file
  *	@filp: file pointer to tty
@@ -2028,8 +2091,6 @@ static int tty_open(struct inode *inode, struct file *filp)
 {
 	struct tty_struct *tty;
 	int noctty, retval;
-	struct tty_driver *driver = NULL;
-	int index;
 	dev_t device = inode->i_rdev;
 	unsigned saved_flags = filp->f_flags;
 
@@ -2040,53 +2101,15 @@ retry_open:
 	if (retval)
 		return -ENOMEM;
 
-	index  = -1;
-	retval = 0;
-
 	tty = tty_open_current_tty(device, filp);
-	if (!tty) {
-		mutex_lock(&tty_mutex);
-		driver = tty_lookup_driver(device, filp, &index);
-		if (IS_ERR(driver)) {
-			retval = PTR_ERR(driver);
-			goto err_unlock;
-		}
-
-		/* check whether we're reopening an existing tty */
-		tty = tty_driver_lookup_tty(driver, inode, index);
-		if (IS_ERR(tty)) {
-			retval = PTR_ERR(tty);
-			goto err_unlock;
-		}
-
-		if (tty) {
-			mutex_unlock(&tty_mutex);
-			retval = tty_lock_interruptible(tty);
-			if (retval) {
-				if (retval == -EINTR)
-					retval = -ERESTARTSYS;
-				goto err_unref;
-			}
-			/* safe to drop the kref from tty_driver_lookup_tty() */
-			tty_kref_put(tty);
-			retval = tty_reopen(tty);
-			if (retval < 0) {
-				tty_unlock(tty);
-				tty = ERR_PTR(retval);
-			}
-		} else { /* Returns with the tty_lock held for now */
-			tty = tty_init_dev(driver, index);
-			mutex_unlock(&tty_mutex);
-		}
-
-		tty_driver_kref_put(driver);
-	}
+	if (!tty)
+		tty = tty_open_by_driver(device, inode, filp);
 
 	if (IS_ERR(tty)) {
+		tty_free_file(filp);
 		retval = PTR_ERR(tty);
 		if (retval != -EAGAIN || signal_pending(current))
-			goto err_file;
-		tty_free_file(filp);
+			return retval;
 		schedule();
 		goto retry_open;
 	}
@@ -2157,15 +2180,6 @@ retry_open:
 	read_unlock(&tasklist_lock);
 	tty_unlock(tty);
 	return 0;
-err_unlock:
-	mutex_unlock(&tty_mutex);
-err_unref:
-	/* after locks to avoid deadlock */
-	if (!IS_ERR_OR_NULL(driver))
-		tty_driver_kref_put(driver);
-err_file:
-	tty_free_file(filp);
-	return retval;
 }
 
 
-- 
2.7.0