Nemo misreports free space for root filesystem on Fedora Atomic 42+

Distribution

Fedora 42, Atomic Desktop

Package version

6.4.5

Frequency

Always

Bug description

In the places sidebar, the "File System" link to the root directory (/) misleadingly states that the root filesystem is 100% full ("Free space: 0 bytes" in the tooltip). Likewise in the status bar at the bottom of the window when in the root directory.

This occurs on systems where the root directory is mounted read-only using composefs, which is newly enabled for Fedora Atomic Desktops as of Fedora 42 (currently in beta but scheduled to be released next week). As noted here:

The main visible change will be that the root filesystem (/) is now small and full (a few MB, 100% used). The real root is mounted in /sysroot and most of the data is stored in /var.

Steps to reproduce

Install Nemo on version 42 (beta if before April 15) of any Fedora Atomic Desktop (Silverblue, Kinoite, etc.), and open Nemo to the root directory. You can also directly check the filesystem data being queried with the following Python code:

import os
print(os.statvfs("/").f_bfree)
print(os.statvfs("/sysroot").f_bfree)

Expected behavior

The root directory should use filesystem statistics for /sysroot (rather than /) to determine free space on Fedora Atomic Desktop and similar systems using composefs, as this reflects actual used and available space on the partition.

Additional information

No response

Start by reproducing the issue with the provided Python os.statvfs checks for / and /sysroot on Fedora Atomic 42+, then locate Nemo's C code that obtains filesystem statistics for the places sidebar and root-directory status bar. Done means those displays report free space from /sysroot for composefs-based systems while preserving correct behavior elsewhere.