cd_acquire() works like bd_acquire() to get cdev by an inode,
this commit is a preparation for lookup_cdev().
Signed-off-by: Dongsheng Yang <yangds.fnst@xxxxxxxxxxxxxx>
---
fs/char_dev.c | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/fs/char_dev.c b/fs/char_dev.c
index ea06a3d..e818faa 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -439,6 +439,41 @@ static int exact_lock(dev_t dev, void *data)
return cdev_get(p) ? 0 : -1;
}
+struct cdev *cd_acquire(struct inode *inode)
+{
+ struct cdev *cdev;
+ struct cdev *new = NULL;
+
+ spin_lock(&cdev_lock);
+ cdev = inode->i_cdev;
+ if (!cdev) {
+ struct kobject *kobj;
+ int idx;
+ spin_unlock(&cdev_lock);
+ kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
+ if (!kobj) {
+ cdev = NULL;
+ goto out;
+ }
+ new = container_of(kobj, struct cdev, kobj);
+ spin_lock(&cdev_lock);
+ /* Check i_cdev again in case somebody beat us to it while
+ we dropped the lock. */
+ cdev = inode->i_cdev;
+ if (!cdev) {
+ inode->i_cdev = cdev = new;
+ list_add(&inode->i_devices, &cdev->list);
+ }
+ }
+
+ if (!cdev_get(cdev))
+ cdev = NULL;
+ spin_unlock(&cdev_lock);
+
+out:
+ return cdev;
+}
+
/**
* cdev_add() - add a char device to the system
* @p: the cdev structure for the device
--
1.8.4.2
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