linux-kernel - lguest: lguest_user.c is open() called by the user?

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Date:	Sun, 19 Oct 2014 02:10:08 +0200
From:	Martin Kepplinger <martink@...teo.de>
To:	rusty@...tcorp.com.au
CC:	lguest@...ts.ozlabs.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: lguest: lguest_user.c is open() called by the user?

hi

Just a question for understanding: open() is not implemented in
lguest_user.c's miscdevice. The miscdevice core, in this case, does
_not_ set file->private_data on a user's open() call. Is open() called
by the user here? and do you here _depend_ on file->private_data being
NULL after open()? (could you even?)

Would the following force to NULL be necessary if the miscdevice core
_would_ set private_data?


diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 4263f4c..3d472ea 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -497,6 +497,12 @@ static int close(struct inode *inode, struct file
*file)
        return 0;
 }

+static int open(struct inode *inode, struct file *file)
+{
+       /* assuming the miscdevice core sets private_data on open() */
+       file->private_data = NULL;
+}
+
 /*L:000
  * Welcome to our journey through the Launcher!
  *
@@ -514,6 +520,7 @@ static int close(struct inode *inode, struct file *file)
  */
 static const struct file_operations lguest_fops = {
        .owner   = THIS_MODULE,
+       .open    = open,
        .release = close,
        .write   = write,
        .read    = read,
-- 

thanks
                               martin
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