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package link
import (
"fmt"
"log"
"os"
"syscall"
)
// ensureHardlink ensures l.path is a hard link to l.target.
//
// Idempotency and clobber policy:
// - already the same inode as the target: nothing to do.
// - a different file/link is in the way: it is renamed to "<path>.old"
// before the link is created (matching the symlink resource's behavior).
func ensureHardlink(l *Link) error {
log.Printf("processing hardlink: %s -> %s", l.path, l.target)
if l.target == "" {
return fmt.Errorf("hardlink %s has no target", l.path)
}
targetInfo, err := os.Stat(l.target)
if err != nil {
return fmt.Errorf("failed to stat hardlink target %s: %w", l.target, err)
}
if info, err := os.Lstat(l.path); err == nil {
if sameInode(info, targetInfo) {
log.Printf("hardlink %s already links to %s", l.path, l.target)
return nil
}
old := l.path + ".old"
log.Printf("%s already exists, renaming to %s", l.path, old)
if err := os.Rename(l.path, old); err != nil {
return fmt.Errorf("failed to move existing %s aside: %w", l.path, err)
}
} else if !os.IsNotExist(err) {
return fmt.Errorf("failed to stat %s: %w", l.path, err)
}
if err := os.Link(l.target, l.path); err != nil {
return fmt.Errorf("failed to create hardlink %s -> %s: %w", l.path, l.target, err)
}
log.Printf("created hardlink %s -> %s", l.path, l.target)
return nil
}
// sameInode reports whether two FileInfos refer to the same underlying inode
// (same device and inode number), i.e. they are already hard-linked.
func sameInode(a, b os.FileInfo) bool {
as, aok := a.Sys().(*syscall.Stat_t)
bs, bok := b.Sys().(*syscall.Stat_t)
if !aok || !bok {
return false
}
return as.Dev == bs.Dev && as.Ino == bs.Ino
}
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