sched/clock: support using CLOCKFD to call clock_getres

This patch extends CLOCKFD support to clock_getres(), allowing
applications to query the resolution of PTP clocks through file
descriptors using the standard POSIX clock API.

Key changes include:

1. Move clock_getres() from libc to kernel:
   - Relocated from libs/libc/sched/clock_getres.c to sched/clock/
   - Enables direct kernel-level file descriptor handling
   - Maintains POSIX compliance while adding CLOCKFD support

2. CLOCKFD support in clock_getres():
   - Detects CLOCKFD-encoded clockids using CLOCKFD_TO_FD() check
   - Extracts file descriptor from clockid parameter
   - Validates file descriptor through fs_getfilep()
   - Issues PTP_CLOCK_GETRES ioctl to query clock resolution

3. PTP clock resolution query:
   - Retrieves resolution from PTP clock device via ioctl
   - Returns nanosecond-precision timing resolution
   - Enables applications to determine clock accuracy capabilities
   - Falls back to standard clock resolution for non-CLOCKFD clockids

4. Error handling:
   - Returns EINVAL for invalid CLOCKFD file descriptors
   - Properly manages file reference counting with fs_putfilep()
   - Maintains backward compatibility with existing clock types

5. Build system updates:
   - Updated libs/libc/sched/CMakeLists.txt and Make.defs
   - Updated sched/clock/CMakeLists.txt to include clock_getres.c
   - Ensures proper compilation in kernel context

Usage example:
  int fd = open("/dev/ptp0", O_RDONLY);
  struct timespec res;
  clock_getres(CLOCKFD(fd), &res);  /* Query PTP clock resolution */
  printf("Resolution: %ld.%09ld sec\n", res.tv_sec, res.tv_nsec);
  close(fd);

This completes the basic POSIX clock API support for dynamic PTP clocks,
providing applications with comprehensive clock information access.

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

libs/libc/sched/CMakeLists.txt

@@ -24,7 +24,6 @@ set(SRCS
     sched_getprioritymax.c
     sched_getprioritymin.c
     clock_getcpuclockid.c
-    clock_getres.c
     task_cancelpt.c
     task_setcancelstate.c
     task_setcanceltype.c

libs/libc/sched/Make.defs

@@ -23,9 +23,9 @@
 # Add the sched C files to the build
 
 CSRCS += sched_getprioritymax.c sched_getprioritymin.c
-CSRCS += clock_getcpuclockid.c clock_getres.c
 CSRCS += task_cancelpt.c task_setcancelstate.c task_setcanceltype.c
 CSRCS += task_testcancel.c task_gettid.c
+CSRCS += clock_getcpuclockid.c
 
 ifeq ($(CONFIG_SMP),y)
 CSRCS += sched_cpucount.c

libs/libc/sched/clock_getres.c

@@ -1,80 +0,0 @@
-/****************************************************************************
- * libs/libc/sched/clock_getres.c
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.  The
- * ASF licenses this file to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance with the
- * License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
- * License for the specific language governing permissions and limitations
- * under the License.
- *
- ****************************************************************************/
-
-/****************************************************************************
- * Included Files
- ****************************************************************************/
-
-#include <nuttx/config.h>
-
-#include <stdint.h>
-#include <time.h>
-#include <errno.h>
-#include <debug.h>
-
-#include <nuttx/clock.h>
-
-/****************************************************************************
- * Public Functions
- ****************************************************************************/
-
-/****************************************************************************
- * Name: clock_getres
- *
- * Description:
- *   Clock Functions based on POSIX APIs
- *
- ****************************************************************************/
-
-int clock_getres(clockid_t clock_id, struct timespec *res)
-{
-  clockid_t clock_type = clock_id & CLOCK_MASK;
-  int       ret = OK;
-
-  sinfo("clock_id=%d, clock_type=%d\n", clock_id, clock_type);
-
-  switch (clock_type)
-    {
-      default:
-        serr("Returning ERROR\n");
-        set_errno(EINVAL);
-        ret = ERROR;
-        break;
-
-      case CLOCK_MONOTONIC:
-      case CLOCK_BOOTTIME:
-      case CLOCK_REALTIME:
-      case CLOCK_PROCESS_CPUTIME_ID:
-      case CLOCK_THREAD_CPUTIME_ID:
-
-        /* Form the timspec using clock resolution in nanoseconds */
-
-        res->tv_sec  = 0;
-        res->tv_nsec = NSEC_PER_TICK;
-
-        sinfo("Returning res=(%d,%d)\n", (int)res->tv_sec,
-                                         (int)res->tv_nsec);
-        break;
-    }
-
-  return ret;
-}