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in my study and examine linux kernel code I encountered with function make_request_fn. in this link it says that this function type definition is in include/linux/blkdev.h, line 211 :

typedef void (make_request_fn) (struct request_queue *q, struct bio *bio);

but did not mention where is its implementation as source code in a .c file. my question is where is this function source code?

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typedef void (make_request_fn) (struct request_queue *q, struct bio *bio);

This is not a function declaration. It is definition of function type. Later in the same file include/linux/blkdev.h, line 299, the same name gets the field in request_queue structure.

And in file drivers/md/bcache/request.c on line 1140, there is assigned function flash_dev_make_request to this field, which makes you think that you call function make_request_fn(), but you really call flash_dev_make_request().

It is really basic way of providing Encapsulation and Polymorphism and really basic OOP model in C.

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It seems like different kernel versions have different function layout. I am working on Linux Kernel 4.9. make_request_fn is initialized by blk_queue_make_request() function in blk-core.c.

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