Getting a block from a block device?

[Alexandru Juncu]

On Tue, Nov 8, 2011 at 1:56 PM, Dan Luedtke <maildanrl at googlemail.com> wrote:
> Hallo,
>
> On Tue, Nov 8, 2011 at 12:27 PM, Stephen Gream <poisonthemon at gmail.com> wrote:
>> Once you have the device registered (on /sys or /dev), register a read
>> callback on the file and use copy_to_user to output the data
>
> I read that article you referred to, but I don't think it addresses my
> problem, as I may have been more clear on what I want to achieve
> before. Sorry for that!
> I want to eventually implement a file system, and therefore I am
> studying the kernel sources to get an idea about all that.
>
> Here is my general understanding on how thinks may work :)
>
> virtual file system (VFS) <-[1]-> my file system implementation
> <-[2]-> a block device
>
> As I understood, all these subsystems are running in kernel mode.
>
> For [1] I read vfs.txt and learned about the VFS-API
> For [2] I have no idea where I can find the API documentation, however
> there were some hints on the book "Linux Driver Development" from
> O'Reilly in chapter "block devices". Nothing really helpful, as they
> were talking about registering new block devices. I want to use
> already present devices where I expect my filesystem to be present on.
> To check that, I have to read the first 512 bytes.
>
> The userspace implementation I was talking about previously is
> something like a mkfs.myfilesystem, that's why i referred to fopen()
> there.
>
> Thank you!
>
> Greetings,


While in the kernel you would be able to read the blocks from a device
without using a file path (you don't need to open a file and read from
it). You will need to interact with the IO System.

I would redirect you to learn about struct gendisk and struct bio.