if you wanna open a block device specificallyy
you can look into fs/block_dev.c

struct block_device *open_bdev_exclusive(const char *path, fmode_t mode,
void *holder)

Also i think if you are interested in reading the first sector
then you can probably check the block/genhd.c file
get the disk (i.e struct genhd) then the partition (struct hdpart)
you will be able to get the first sector.

Thanks

On Tue, Nov 8, 2011 at 5:29 PM, rohan puri [off-list ref] wrote:

On Tue, Nov 8, 2011 at 5:26 PM, Dan Luedtke [off-list ref]wrote:

quoted

Hallo,

On Tue, Nov 8, 2011 at 12:27 PM, Stephen Gream [off-list ref]
wrote:

quoted

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,

Dan
--
Dan Luedtke
http://www.danrl.de

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Dan,

You need to look at other block-based file systems in the kernel sources
in fs dir for examples and understand how they do it.

Regards,
Rohan Puri

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