[PATCH v2 07/15] misc: nnpi: Disallow host memory resource access if no NNP-I devices exist

[Guy Zadicario <guy.zadicario@intel.com>]

There is no point allowing a user application to create host resources
on a system that does not equipped with any NNP-I devices.
Fail openning the nnpi_host character device when no NNP-I devices are
attached.
It is OK to do that check without any synchronization as a race would not
be an issue.

Signed-off-by: Guy Zadicario <guy.zadicario@intel.com>
Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
 drivers/misc/intel-nnpi/device.c       | 5 +++++
 drivers/misc/intel-nnpi/device.h       | 2 ++
 drivers/misc/intel-nnpi/host_chardev.c | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/drivers/misc/intel-nnpi/device.c b/drivers/misc/intel-nnpi/device.c
index 0f98398..a3c6a1d 100644
--- a/drivers/misc/intel-nnpi/device.c
+++ b/drivers/misc/intel-nnpi/device.c
@@ -13,6 +13,11 @@
 
 static DEFINE_IDA(dev_ida);
 
+bool nnpdev_no_devices(void)
+{
+	return ida_is_empty(&dev_ida);
+}
+
 /**
  * nnpdev_init() - initialize NNP-I device structure.
  * @nnpdev: device to be initialized
diff --git a/drivers/misc/intel-nnpi/device.h b/drivers/misc/intel-nnpi/device.h
index 7d7ef60..562bbc4 100644
--- a/drivers/misc/intel-nnpi/device.h
+++ b/drivers/misc/intel-nnpi/device.h
@@ -36,6 +36,8 @@ struct nnp_device_ops {
 	int (*cmdq_write_mesg)(struct nnp_device *nnpdev, u64 *msg, u32 size);
 };
 
+bool nnpdev_no_devices(void);
+
 /*
  * Functions exported by the device framework module which are
  * called by the lower layer NNP-I device driver module
diff --git a/drivers/misc/intel-nnpi/host_chardev.c b/drivers/misc/intel-nnpi/host_chardev.c
index 6048fda..fad5954 100644
--- a/drivers/misc/intel-nnpi/host_chardev.c
+++ b/drivers/misc/intel-nnpi/host_chardev.c
@@ -217,6 +217,13 @@ static int host_open(struct inode *inode, struct file *f)
 	if (!is_host_file(f))
 		return -EINVAL;
 
+	/*
+	 * No point to serve host resource creation while no
+	 * NNP-I devices exist in the system.
+	 */
+	if (nnpdev_no_devices())
+		return -ENODEV;
+
 	user_info = kzalloc(sizeof(*user_info), GFP_KERNEL);
 	if (!user_info)
 		return -ENOMEM;
-- 
1.8.3.1