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

[Martin Kepplinger]

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,

[Rusty Russell]

Post by Martin Kepplinger
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?

Hi Martin!

Yes, the private_data is NULL on a new file. See
get_empty_filp in fs/file_table.c, which does kmem_cache_zalloc
(zeroing all the contents).

So this isn't necessary here.

Thanks!
Rusty.

Post by Martin Kepplinger
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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