how to read block device size from sysfs?

["Gerd v. Egidy" <lists@egidy.de>]

Hi,

I want to read the size of a block device in bytes from sysfs.

There are /sys/block/<device>/size and 
/sys/block/<device>/<device><partition>/size.

But these values are reported in sectors, not in bytes. As discs with 4K 
sectors are on the horizon now, I don't want to make wrong assumptions on the 
sector size.

So what is the correct sector size for /sys/block/<device>/size?

/sys/block/<device>/queue/logical_block_size,
/sys/block/<device>/queue/physical_block_size or something else?

While searching for an answer I've stumbled across some reports about drives 
lying about their sector sizes to "improve" compatibility. Is there some best 
practice to still get the correct size in bytes?

Kind regards,

Gerd

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