Disk (Linux): Don't mark / as read-only in Fedora Atomic

[ledif]

Fedora Atomic and its derivatives such as Bazzite use a mix of composefs for the system mount and btrfs for variable read-write data. The composefs mount is correctly marked as read-only but the btrfs partition is also marked as read-only because the partition is mounted in several different places with a mix of read-write and read-only.

As an example:

/dev/nvme1n1p3 /sysroot btrfs ro,seclabel,relatime,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/root 0 0
/dev/nvme1n1p3 /etc btrfs rw,seclabel,relatime,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/root 0 0
/dev/nvme1n1p3 /sysroot/ostree/deploy/default/var btrfs rw,seclabel,relatime,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/root 0 0
/dev/nvme1n1p3 /var btrfs rw,seclabel,noatime,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/var 0 0
/dev/nvme1n1p3 /var/home btrfs rw,seclabel,noatime,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/home 0 0

The main btrfs partition should not be considered read-only because it happens to contain a read-only subvolume. This PR enhances the read-only detection logic to see if any of the mounts for the same device are read-write and if so mark the whole device as read-write.

Screenshots

Current default Bazzite fastfetch:

Bazzite's fastfetch with the read-only mounts hidden. Notice that it hides both the composefs mount (which we want to hide) and the main btrfs mount (which we do not want to hide):

Bazzite's fastfetch with this patch and read-only mounts hidden. Notice the main btrfs mount is there as expected:

[Copilot]

Pull Request Overview

This PR adjusts read-only detection for Btrfs mounts on Fedora Atomic systems by checking all mount points for a device before marking it as read-only, preventing the main Btrfs partition from being hidden when only one subvolume is ro.

• Added isReadOnly() helper that scans /proc/mounts for R/W instances of the same Btrfs device
• Switched detectType() to use isReadOnly() instead of a direct ro option check

Comments suppressed due to low confidence (1)

src/detection/disk/disk_linux.c:221

• Introduce unit tests for isReadOnly(), especially to verify behavior when the same Btrfs device has both read-only and read-write mounts.

static bool isReadOnly(FFDisk* currentDisk, struct mntent* device)

[Copilot]

[nitpick] Avoid using the literal string "btrfs"; consider defining a constant or using an enum for filesystem types to improve readability and reduce risk of typos.

Suggested change

	if (ffStrbufEqualS(&currentDisk->filesystem, "btrfs"))
	if (ffStrbufEqualS(&currentDisk->filesystem, FILESYSTEM_BTRFS))

[Copilot]

[nitpick] Opening and scanning /proc/mounts on every call could add I/O overhead; consider caching the mounts list once per scan or reusing the open file between disk checks.

Suggested change

	FILE* mountsFile = setmntent("/proc/mounts", "r");
	if (mountsFile != NULL)
	{
	struct mntent* otherDev;
	while ((otherDev = getmntent(mountsFile)))
	{
	// If same device but not read-only, then this device has R/W access
	if (ffStrEquals(otherDev->mnt_fsname, deviceName) &&
	!hasmntopt(otherDev, MNTOPT_RO))
	{
	endmntent(mountsFile);
	return false;
	}
	}
	endmntent(mountsFile);
	}
	static struct mntent** cachedMounts = NULL;
	static size_t cachedMountsCount = 0;
	if (cachedMounts == NULL)
	{
	FILE* mountsFile = setmntent("/proc/mounts", "r");
	if (mountsFile != NULL)
	{
	struct mntent* entry;
	size_t count = 0;
	while ((entry = getmntent(mountsFile)))
	count++;
	rewind(mountsFile);
	cachedMounts = malloc(count * sizeof(struct mntent*));
	cachedMountsCount = count;
	count = 0;
	while ((entry = getmntent(mountsFile)))
	{
	cachedMounts[count] = malloc(sizeof(struct mntent));
	*cachedMounts[count] = *entry;
	count++;
	}
	endmntent(mountsFile);
	}
	}
	for (size_t i = 0; i < cachedMountsCount; i++)
	{
	struct mntent* otherDev = cachedMounts[i];
	// If same device but not read-only, then this device has R/W access
	if (ffStrEquals(otherDev->mnt_fsname, deviceName) &&
	!hasmntopt(otherDev, MNTOPT_RO))
	{
	return false;
	}
	}

[CarterLi]

Please upload your /proc/mounts