sysfs block size count

Question

Is the file located under:

/sys/block/<xxx>/size

Constantly referencing to 512 byte block count, or is there any special cases where the block count changes?

I'm curious because:

thinkpad :: /sys/block/sdf % cat queue/physical_block_size                                                                                                                         
4096
thinkpad :: /sys/block/sdf % cat queue/logical_block_size                                                                                                                          
4096
thinkpad :: /sys/block/sdf % cat size                                                                                                                                              
15408640

15408640 * 512 bytes / 1000000000 = ~8GB -> the size of my device, its correct but the device is a 4K block device.

score 4 · Accepted Answer · answered Aug 05 '16 at 00:47

The size entry returns the nr_sects field of the block device structure. Traditionally, in Unix disk size contexts, “sector” or “block” means 512 bytes, regardless of what the manufacturer of the underlying hardware might call a “sector” or “block”. I can't find authoritative documentation, but looking at the Linux source code (e.g. 1) 2) it looks like the nr_sects field is indeed expressed in units of 512 bytes.

You can approach it another way: since there is no file reporting the unit, it has to be a constant unit, otherwise applications wouldn't know what the value means. (The queue subdirectory is not necessarily present, it depends on the block device.)

sysfs block size count

1 Answers1