Subject: Re: bug#64588: BUG: stat -f incorrectly reports a BTRFS device as a tmpfs

From: Pádraig Brady <[email-masked]>
Date: Thu, 13 Jul 2023 10:59:48 +0100

tag 64588 notabug
close 64588
stop

On 12/07/2023 23:46, support wrote:
> coreutils version 9.1-1 on Debian testing, but also exists in previous
> versions.
> 
> 
> Example:
> 
> stat -f  /dev/sdb
>     File: "/dev/sdb"
>       ID: eb91af7d7bda02dd Namelen: 255     Type: tmpfs
> Block size: 4096       Fundamental block size: 4096
> Blocks: Total: 2012292    Free: 2012292    Available: 2012292
> Inodes: Total: 2012292    Free: 2011839
> 
> 
> stat -f  /dev/disk/by-uuid/6abaa68a-2670-4d8b-8d2a-fd7321df9242
>     File: "/dev/disk/by-uuid/6abaa68a-2670-4d8b-8d2a-fd7321df9242"
>       ID: eb91af7d7bda02dd Namelen: 255     Type: tmpfs
> Block size: 4096       Fundamental block size: 4096
> Blocks: Total: 2012292    Free: 2012292    Available: 2012292
> Inodes: Total: 2012292    Free: 2011839
> 
> 
> blkid /dev/sdb
> /dev/sdb: UUID="6abaa68a-2670-4d8b-8d2a-fd7321df9242"
> UUID_SUB="d15f1846-8f18-4ba0-9e2a-a6aaa7bbf83b" BLOCK_SIZE="4096"
> TYPE="btrfs"
> 
> 
> Not sure why the reported fstype is wrong but obviously it is a bug.

This is expected. From the info docs:

"stat does not search for specified device nodes in the file system list,
instead operating on them directly"

I.e. /dev/sdb is a device node in the /dev file system, which is tmpfs.
You can confirm this with:

   strace -e statfs stat -f -c %T /dev/sdb
   strace -e statfs df --output=fstype /dev/sdb

If you wanted to operate on a file system mounted on the device node you could:

   stat -f $(df --output=target /dev/sdb | tail -n1)

cheers,
Pádraig