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

sched/clock/CMakeLists.txt

@@ -23,6 +23,7 @@
 set(SRCS
     clock.c
     clock_initialize.c
+    clock_getres.c
     clock_settime.c
     clock_gettime.c
     clock_realtime2absticks.c

sched/clock/Make.defs

@@ -22,7 +22,7 @@
 
 CSRCS += clock.c clock_initialize.c clock_settime.c clock_gettime.c
 CSRCS += clock_systime_ticks.c clock_systime_timespec.c clock_sched_ticks.c
-CSRCS += clock_perf.c clock_realtime2absticks.c
+CSRCS += clock_perf.c clock_realtime2absticks.c clock_getres.c
 
 # Unless a driver with a more accurate version of up_*delay is enabled, always
 # include the base delay definition (busy-loop) as a minimum-viable product. We

sched/clock/clock_getres.c

@@ -1,5 +1,5 @@
 /****************************************************************************
- * libs/libc/sched/clock_getres.c
+ * sched/clock/clock_getres.c
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -24,14 +24,14 @@
  * Included Files
  ****************************************************************************/
 
-#include <nuttx/config.h>
-
 #include <stdint.h>
 #include <time.h>
 #include <errno.h>
 #include <debug.h>
 
 #include <nuttx/clock.h>
+#include <nuttx/fs/fs.h>
+#include <nuttx/timers/ptp_clock.h>
 
 /****************************************************************************
  * Public Functions
@@ -74,6 +74,23 @@ int clock_getres(clockid_t clock_id, struct timespec *res)
         sinfo("Returning res=(%d,%d)\n", (int)res->tv_sec,
                                          (int)res->tv_nsec);
         break;
+
+#ifdef CONFIG_PTP_CLOCK
+      case CLOCK_FD:
+        {
+          FAR struct file *filep;
+
+          ret = ptp_clockid_to_filep(clock_id, &filep);
+          if (ret < 0)
+            {
+              return ret;
+            }
+
+          ret = file_ioctl(filep, PTP_CLOCK_GETRES, res);
+          fs_putfilep(filep);
+        }
+        break;
+#endif
     }
 
   return ret;