To: linux-btrfs@vger.kernel.org
From: Duncan <1i5t5.duncan@cox.net>
Subject: Re: btrfs filesystem show _exact_ freaking size?
Date: Tue, 18 Nov 2014 12:41:55 +0000 (UTC)
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Robert White posted on Tue, 18 Nov 2014 02:39:48 -0800 as excerpted:

> How does one get the exact size (in blocks preferably, but bytes okay)
> of the filesystem inside a partition? I know how to get the partition
> size, but that's not useful when shrinking a partition...

> There needs to be an option to btrfs filesystem show that will tell you
> XXXXXblocks, not Y.ZZ terabytes.

While having a btrfs fi show option for that would be nice, take a look 
at the output of btrfs-show-super.

The dev_item.total_bytes line appears to be the total filesystem bytes -- 
at least here on my exactly-8-GiB partitions, that's /exactly/ what it 
shows, 8589934592, which is 8*1024*1024*1024, and my /exactly/ 256 MiB 
partition shows 268435456, /exactly/ 256 MiB, as well.

The total_bytes line is the full /filesystem/ size, which should be the 
same as the dev_item.total_bytes number on a single-device-filesystem.  
Of course on my two-device btrfs filesystems here it's showing double the 
single-device size, which is as it should be.

But you're correct, having a btrfs fi show option for that would be more 
end-user friendly.  The btrfs-show-super output is rather low-level for 
that, but it does work.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman