os2: improve absolute/full path handling for posix

core/os/os2/file_posix_freebsd.odin

@@ -0,0 +1,47 @@
+//+private
+package os2
+
+import "base:runtime"
+
+import "core:c"
+import "core:sys/posix"
+
+_posix_absolute_path :: proc(fd: posix.FD, name: string, allocator: runtime.Allocator) -> (path: cstring, err: Error) {
+	// NOTE(Feoramund): The situation isn't ideal, but this was the best way I
+	// could find to implement this. There are a couple outstanding bug reports
+	// regarding the desire to retrieve an absolute path from a handle, but to
+	// my knowledge, there hasn't been any work done on it.
+	//
+	// https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=198570
+	//
+	// This may be unreliable, according to a comment from 2023.
+
+	KInfo_File :: struct {
+		structsize: c.int,
+		type:       c.int,
+		fd:         c.int,
+		ref_count:  c.int,
+		flags:      c.int,
+		pad0:       c.int,
+		offset:     i64,
+
+		// NOTE(Feoramund): This field represents a complicated union that I am
+		// avoiding implementing for now. I only need the path data below.
+		_union: [336]byte,
+
+		path: [posix.PATH_MAX]c.char,
+	}
+
+	F_KINFO :: 22
+
+	kinfo: KInfo_File
+	kinfo.structsize = size_of(KInfo_File)
+
+	res := posix.fcntl(fd, posix.FCNTL_Cmd(F_KINFO), &kinfo)
+	if res == -1 {
+		err = _get_platform_error()
+		return
+	}
+
+	return clone_to_cstring(string(cstring(&kinfo.path[0])), allocator)
+}