[Bug 2126059] [NEW] stat filesystem type print output incorrect for cgroups

[Maciej Borzecki]

Public bug reported:

The uutils version does not seem to report the filesystem type
correctly:

root at u1:~# stat -f --printf='%T\n' /sys//fs/cgroup/
UNKNOWN (0x63677270)

root at u1:~# stat -f /sys/fs/cgroup/
  File: "/sys/fs/cgroup/"
    ID: 586d3e54c17eb980 Namelen: 255     Type: UNKNOWN (0x63677270)
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 0          Free: 0          Available: 0
Inodes: Total: 0          Free: 0

root at u1:~# stat --version
stat (uutils coreutils) 0.1.0

Whereas the GNU one produces correct output:

root at u1:~# gnustat -f --printf='%T\n' /sys//fs/cgroup/
cgroup2fs

root at u1:~# gnustat -f /sys/fs/cgroup/
  File: "/sys/fs/cgroup/"
    ID: 586d3e54c17eb980 Namelen: 255     Type: cgroup2fs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 0          Free: 0          Available: 0
Inodes: Total: 0          Free: 0

root at u1:~# dpkg -l gnu-coreutils rust-coreutils
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version                            Architecture Description
+++-==============-==================================-============-==========================================
ii  gnu-coreutils  9.5-1ubuntu3                       amd64        GNU core utilities
ii  rust-coreutils 0.1.0+git20250813.4af2a84-0ubuntu7 amd64        Universal coreutils utils, written in Rust

** Affects: rust-coreutils (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2126059

Title:
  stat filesystem type print output incorrect for cgroups

Status in rust-coreutils package in Ubuntu:
  New

Bug description:
  The uutils version does not seem to report the filesystem type
  correctly:

  root at u1:~# stat -f --printf='%T\n' /sys//fs/cgroup/
  UNKNOWN (0x63677270)

  root at u1:~# stat -f /sys/fs/cgroup/
    File: "/sys/fs/cgroup/"
      ID: 586d3e54c17eb980 Namelen: 255     Type: UNKNOWN (0x63677270)
  Block size: 4096       Fundamental block size: 4096
  Blocks: Total: 0          Free: 0          Available: 0
  Inodes: Total: 0          Free: 0

  root at u1:~# stat --version
  stat (uutils coreutils) 0.1.0

  Whereas the GNU one produces correct output:

  root at u1:~# gnustat -f --printf='%T\n' /sys//fs/cgroup/
  cgroup2fs

  root at u1:~# gnustat -f /sys/fs/cgroup/
    File: "/sys/fs/cgroup/"
      ID: 586d3e54c17eb980 Namelen: 255     Type: cgroup2fs
  Block size: 4096       Fundamental block size: 4096
  Blocks: Total: 0          Free: 0          Available: 0
  Inodes: Total: 0          Free: 0

  root at u1:~# dpkg -l gnu-coreutils rust-coreutils
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name           Version                            Architecture Description
  +++-==============-==================================-============-==========================================
  ii  gnu-coreutils  9.5-1ubuntu3                       amd64        GNU core utilities
  ii  rust-coreutils 0.1.0+git20250813.4af2a84-0ubuntu7 amd64        Universal coreutils utils, written in Rust

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