Linux 4 block device driver infrastructure

[Alexandru Goia]

Greetings !

I am a Unix/Linux hobbyist from Romania, interested in kernel stuff.
I need some clarifications, related to block device subsystem in Linux 4,
so I will ask them here, if you can answer me, please...

1) Why (in Linux 4) in struct block_device_operations, the
(*open)(struct block_device *, fmode_t)
has a different signature than the (*release)(struct gendisk *,
fmode_t) ? Why open()
uses block_device, while release() uses gendisk ? They are both in a struct
block_device_operations. Why they not refer to the same thing ?

I understand that gendisk refer to a real disk, and block_device (s)
to logical disk (s)
and partitions. But why the kernel developers have chosen to use
different signatures ?

2) Release() is also synonim to close() ?
3) Why is not explicitely present a close() function ?
4) Why struct gendisk does not have inside it pointers to struct block_device ?

Thank you very much,
Alexander,
Computer hobbyist,
Romania

Please answer also to my personal address : <goia.i.alexandru@xxxxxxxxx>