//go:build linux

package hostcollect

import "syscall"

// statFS reads capacity and inode usage for one mount point. statfs(2) is a read-only
// syscall that needs no capability, which keeps the agent inside cap_drop: [ALL].
//
// "Used" follows df: total blocks minus free blocks, so the filesystem's reserved
// blocks count as used rather than as available headroom the operator does not have.
func statFS(path string) (FilesystemUsage, error) {
	var stat syscall.Statfs_t
	if err := syscall.Statfs(path, &stat); err != nil {
		return FilesystemUsage{}, err
	}
	blockSize := uint64(stat.Bsize) //nolint:gosec,unconvert // Bsize is int64 on some arches, uint32 on others
	if blockSize == 0 {
		return FilesystemUsage{}, nil
	}
	blocks := stat.Blocks
	free := stat.Bfree
	if free > blocks {
		free = blocks
	}
	usage := FilesystemUsage{
		CapacityBytes: blocks * blockSize,
		UsedBytes:     (blocks - free) * blockSize,
		InodesTotal:   stat.Files,
	}
	if stat.Files > 0 {
		freeInodes := stat.Ffree
		if freeInodes > stat.Files {
			freeInodes = stat.Files
		}
		usage.InodesUsed = stat.Files - freeInodes
	}
	return usage, nil
}