cdev_init and struct file_operations
In the book Linux Device Drivers a struct cdev is setup like this: static void scull_setup_cdev(struct scull_dev *dev, int index) { int err, devno = MKDEV(scull_major, scull_minor + index); cdev_init(&dev->cdev, &scull_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &scull_fops; ... the code for cdev_init does this: void cdev_init(struct cdev *cdev, const struct file_operations *fops) { memset(cdev, 0, sizeof *cdev); INIT_LIST_HEAD(&cdev->list); kobject_init(&cdev->kobj, &ktype_cdev_default); cdev->ops = fops; } Why does the code from ldd3 set dev->cdev.ops = &scull_fops again? Doesn't cdev_init already do that?
On Tue, 26 Aug 2014 20:48:41 -0400, John de la Garza said:
In the book Linux Device Drivers a struct cdev is setup like this:
static void scull_setup_cdev(struct scull_dev *dev, int index) { int err, devno = MKDEV(scull_major, scull_minor + index);
cdev_init(&dev->cdev, &scull_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &scull_fops; ...
the code for cdev_init does this: void cdev_init(struct cdev *cdev, const struct file_operations *fops) { memset(cdev, 0, sizeof *cdev); INIT_LIST_HEAD(&cdev->list); kobject_init(&cdev->kobj, &ktype_cdev_default); cdev->ops = fops; }
Why does the code from ldd3 set dev->cdev.ops = &scull_fops again?
Probably because when ldd3 was written several years ago, cdev_init() didn't set it, so it wasn't "again"....
Doesn't cdev_init already do that?
It does *now*. Remember that ldd3 was written about 6 million lines of code ago....
On Tue, Aug 26, 2014 at 09:18:57PM -0400, Valdis.Kletnieks@vt.edu wrote:
On Tue, 26 Aug 2014 20:48:41 -0400, John de la Garza said:
Why does the code from ldd3 set dev->cdev.ops = &scull_fops again?
Probably because when ldd3 was written several years ago, cdev_init() didn't set it, so it wasn't "again"....
Doesn't cdev_init already do that?
It does *now*.
Remember that ldd3 was written about 6 million lines of code ago....
It did then, too (unless I'm missing something) linux$ git branch * (detached from v2.6.12) master from v2.6.12 void cdev_init(struct cdev *cdev, struct file_operations *fops) { memset(cdev, 0, sizeof *cdev); INIT_LIST_HEAD(&cdev->list); cdev->kobj.ktype = &ktype_cdev_default; kobject_init(&cdev->kobj); cdev->ops = fops; }
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John de la Garza -
Valdis.Kletnieks＠vt.edu