BLKGETSIZE64 (bytes or sectors?)

[email protected] wrote, and he is right:

Yes, in bytes. blkpg.c has to be fixed.
Several people submitted patches. Sooner or later I suppose this will be fixed.

Then Tim Pepper answered, and he is wrong:

Wouldn't it be better to do the following (against 2.4.17).

+ else {
+ if (hardsect_size[MAJOR(dev)][MINOR(dev)]) {
+ ullval *= hardsect_size[MAJOR(dev)][MINOR(dev)];
+ } else {
+ ullval *= 512;
+ }
return put_user(ullval, (u64 *)arg);
+ }

You see, the 512 here is 512, and has no relation to hardware sector size. Multiplying with hardsect_size[][] is a bad bug.

Indeed, you can check this in fs/partitions/msdos.c, where one reads

	int sector_size = get_hardsect_size(to_kdev_t(bdev->bd_dev)) / 512;
	...
	offs = START_SECT(p)*sector_size;
	size = NR_SECTS(p)*sector_size;
	...
	add_gd_partition(...);

So, indeed, we have already multiplied by hardsect_size, struct gendisk uses sectors of size 512, independent of the hardware, and we must not again multiply by hardsect_size.

Unfortunately Matt Domsch replied:

but he meant: No!

Andries

Doh. It's obviously much cleaner and more efficient that way.

Have any of the other patch submitters added a comment to note this in include/linux/genhd.h? hd_struct doesn't have any mention of start_sect and nr_sect being stored in sectors of 512bytes. But maybe that's just to weed out fools like me.

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*  tpepper@vato dot org             * Venimus, Vidimus, *
*  http://www.vato.org/~tpepper     * Dolavimus         *
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