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SubjectRe: what is teh current meaning of blk_size?
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"A month of sundays ago Martin Dalecki wrote:"
> "Peter T. Breuer" wrote:
> > Is blk_size[][] supposed to contain the size in KB or blocks?
> There is no rumor it's in blocks.
>
> There are three level of block size measurements in linux:
>
> 1. FS level one. (page chunks most of time main exceptions are dos and
> isofs)
> 2. Driver level one. (nearly always 1024, main exception are ATAPI
> cdrom)
> 3. Hardware device level one. (nearly always 512, only prehistoric SCSI
> drives from the stone age are exceptional and providing 256 byte sized
> block. We discovered them druing our archeological efforts recently
> under
> a thick layer of mood...)
>
> It's left as an exercies to the reader which one of the sparse
> matrices in ll_rw_blk.c is declaring which ;-).
> ...

Uh, thanks! I was looking at fs/block_dev.c.

if (blk_size[MAJOR(dev)])
size = ((loff_t) blk_size[MAJOR(dev)][MINOR(dev)] << BLOCK_SIZE_BITS) >> blocksize_bits;

which sets the size to the entered blk_size << 10 - blksize_bits.

I missed that BLOCK_SIZE_BITS was constant but blksize_bits is variable.
Amongst other things.


> OK I was to fast to figure it out:
>
> /*
> * blk_size contains the size of all block-devices in units of 1024 byte
> * sectors:

But this is not so .. it is the default, not the rule. And it is only
the default if the block size is the default value.

> int * blk_size[MAX_BLKDEV];
>
> /*
> * blksize_size contains the size of all block-devices:

Err .... they mean the BLOCK SIZE of all ...

> int * blksize_size[MAX_BLKDEV];
>
> /*
> * hardsect_size contains the size of the hardware sector of a device.

Never used. Thanks for clearing that up!

If you knew if the meaning of blk_size had ever changed, and when in
terms of kernel version, that would also be very very helpful.

Peter

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