Linux 4 block device driver infrastructure

jim.cromie at jim.cromie at
Thu Dec 7 20:25:48 EST 2023

On Thu, Nov 30, 2023 at 9:08 AM Alexandru Goia
<goia.i.alexandru at> wrote:
> 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 ?

in linux current, its not like that:

struct block_device_operations {
        void (*submit_bio)(struct bio *bio);
        int (*poll_bio)(struct bio *bio, struct io_comp_batch *iob,
                        unsigned int flags);
        int (*open)(struct gendisk *disk, blk_mode_t mode);
        void (*release)(struct gendisk *disk);

Old books are still useful, but new code is a much better place to look.

> 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
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