WasmFS: Use emscripten_date_now for time computations (#20014)

That gives millisecond precision, which I think is probably more than enough, and as
the test updates show, it reduces code size.

Author: kripken

system/lib/standalone/standalone.c

@@ -172,15 +172,23 @@ int emscripten_resize_heap(size_t size) {
   return 0;
 }
 
-weak double emscripten_get_now(void) {
+// Call clock_gettime with a particular clock and return the result in ms.
+static double clock_gettime_ms(clockid_t clock) {
   struct timespec ts;
-  if (clock_gettime(CLOCK_MONOTONIC, &ts)) {
+  if (clock_gettime(clock, &ts)) {
     return 0;
   }
-  // emscripten_get_now returns time in milliseconds (as a double)
   return (double)ts.tv_sec * 1000 + (double)ts.tv_nsec / 1000000;
 }
 
+weak double emscripten_get_now(void) {
+  return clock_gettime_ms(CLOCK_MONOTONIC);
+}
+
+weak double emscripten_date_now(void) {
+  return clock_gettime_ms(CLOCK_REALTIME);
+}
+
 // C++ ABI
 
 #if EMSCRIPTEN_NOCATCH

system/lib/wasmfs/file.h

@@ -11,12 +11,12 @@
 
 #include "support.h"
 #include <assert.h>
+#include <emscripten.h>
 #include <emscripten/html5.h>
 #include <map>
 #include <mutex>
 #include <optional>
 #include <sys/stat.h>
-#include <time.h>
 #include <variant>
 #include <vector>
 #include <wasi/api.h>
@@ -97,9 +97,7 @@ class File : public std::enable_shared_from_this<File> {
 protected:
   File(FileKind kind, mode_t mode, backend_t backend)
     : kind(kind), mode(mode), backend(backend) {
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    atime = mtime = ctime = ts;
+    atime = mtime = ctime = emscripten_date_now();
   }
 
   // A mutex is needed for multiple accesses to the same file.
@@ -111,9 +109,9 @@ class File : public std::enable_shared_from_this<File> {
 
   mode_t mode = 0; // User and group mode bits for access permission.
 
-  struct timespec atime; // Time when the content was last accessed.
-  struct timespec mtime; // Time when the file content was last modified.
-  struct timespec ctime; // Time when the file node was last modified.
+  double atime; // Time when the content was last accessed, in ms.
+  double mtime; // Time when the file content was last modified, in ms.
+  double ctime; // Time when the file node was last modified, in ms.
 
   // Reference to parent of current file node. This can be used to
   // traverse up the directory tree. A weak_ptr ensures that the ref
@@ -317,35 +315,29 @@ class File::Handle {
     // directory, for example).
     file->mode = (file->mode & S_IFMT) | (mode & ~S_IFMT);
   }
-  struct timespec getCTime() {
+  double getCTime() {
     return file->ctime;
   }
-  void setCTime(struct timespec time) { file->ctime = time; }
+  void setCTime(double time) { file->ctime = time; }
   // updateCTime() updates the ctime to the current time.
   void updateCTime() {
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    file->ctime = ts;
+    file->ctime = emscripten_date_now();
   }
-  struct timespec getMTime() {
+  double getMTime() {
     return file->mtime;
   }
-  void setMTime(struct timespec time) { file->mtime = time; }
+  void setMTime(double time) { file->mtime = time; }
   // updateMTime() updates the mtime to the current time.
   void updateMTime() {
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    file->mtime = ts;
+    file->mtime = emscripten_date_now();
   }
-  struct timespec getATime() {
+  double getATime() {
     return file->atime;
   }
-  void setATime(struct timespec time) { file->atime = time; }
+  void setATime(double time) { file->atime = time; }
   // updateATime() updates the atime to the current time.
   void updateATime() {
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    file->atime = ts;
+    file->atime = emscripten_date_now();
   }
 
   // Note: parent.lock() creates a new shared_ptr to the same Directory

system/lib/wasmfs/syscalls.cpp

@@ -22,7 +22,6 @@
 #include <sys/stat.h>
 #include <sys/statfs.h>
 #include <syscall_arch.h>
-#include <time.h>
 #include <unistd.h>
 #include <utility>
 #include <vector>
@@ -346,6 +345,18 @@ backend_t wasmfs_get_backend_by_path(const char* path) {
   return parsed.getFile()->getBackend();
 }
 
+static timespec ms_to_timespec(double ms) {
+  long long seconds = ms / 1000;
+  timespec ts;
+  ts.tv_sec = seconds; // seconds
+  ts.tv_nsec = (ms - (seconds * 1000)) * 1000 * 1000; // nanoseconds
+  return ts;
+}
+
+static double timespec_to_ms(timespec ts) {
+  return double(ts.tv_sec) * 1000 + double(ts.tv_nsec) / (1000 * 1000);
+}
+
 int __syscall_newfstatat(int dirfd, intptr_t path, intptr_t buf, int flags) {
   // Only accept valid flags.
   if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_SYMLINK_NOFOLLOW)) {
@@ -386,9 +397,9 @@ int __syscall_newfstatat(int dirfd, intptr_t path, intptr_t buf, int flags) {
   buffer->st_blocks = (buffer->st_size + 511) / 512;
   // Specifies the preferred blocksize for efficient disk I/O.
   buffer->st_blksize = 4096;
-  buffer->st_atim = lockedFile.getATime();
-  buffer->st_mtim = lockedFile.getMTime();
-  buffer->st_ctim = lockedFile.getCTime();
+  buffer->st_atim = ms_to_timespec(lockedFile.getATime());
+  buffer->st_mtim = ms_to_timespec(lockedFile.getMTime());
+  buffer->st_ctim = ms_to_timespec(lockedFile.getCTime());
   return __WASI_ERRNO_SUCCESS;
 }
 
@@ -1135,16 +1146,13 @@ int __syscall_utimensat(int dirFD, intptr_t path_, intptr_t times_, int flags) {
 
   // TODO: Handle tv_nsec being UTIME_NOW or UTIME_OMIT.
   // TODO: Check for write access to the file (see man page for specifics).
-  struct timespec aTime, mTime;
+  double aTime, mTime;
 
   if (times == NULL) {
-    struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
-    aTime = ts;
-    mTime = ts;
+    aTime = mTime = emscripten_date_now();
   } else {
-    aTime = times[0];
-    mTime = times[1];
+    aTime = timespec_to_ms(times[0]);
+    mTime = timespec_to_ms(times[1]);
   }
 
   auto locked = parsed.getFile()->locked();

test/other/metadce/test_metadce_cxx_wasmfs.imports

@@ -1,5 +1,4 @@
 env.__cxa_throw
-env._emscripten_get_now_is_monotonic
 env._wasmfs_copy_preloaded_file_data
 env._wasmfs_get_num_preloaded_dirs
 env._wasmfs_get_num_preloaded_files

test/other/metadce/test_metadce_cxx_wasmfs.jssize

@@ -1 +1 @@
-12559
+12478

test/other/metadce/test_metadce_cxx_wasmfs.sent

@@ -1,5 +1,4 @@
 __cxa_throw
-_emscripten_get_now_is_monotonic
 _wasmfs_copy_preloaded_file_data
 _wasmfs_get_num_preloaded_dirs
 _wasmfs_get_num_preloaded_files
@@ -12,7 +11,6 @@ _wasmfs_stdin_get_char
 abort
 emscripten_date_now
 emscripten_err
-emscripten_get_now
 emscripten_memcpy_big
 emscripten_out
 emscripten_resize_heap

test/other/metadce/test_metadce_cxx_wasmfs.size

@@ -1 +1 @@
-164404
+163645

test/other/metadce/test_metadce_files_wasmfs.exports

@@ -1,4 +1,4 @@
+q
 r
 s
 t
-u

test/other/metadce/test_metadce_files_wasmfs.funcs

@@ -1,4 +1,3 @@
-$__clock_gettime
 $__cxx_global_array_dtor
 $__cxx_global_array_dtor.1
 $__cxx_global_array_dtor.2

test/other/metadce/test_metadce_files_wasmfs.imports

@@ -14,4 +14,3 @@ a.m
 a.n
 a.o
 a.p
-a.q

test/other/metadce/test_metadce_files_wasmfs.jssize

@@ -1 +1 @@
-7116
+7107

test/other/metadce/test_metadce_files_wasmfs.sent

@@ -14,4 +14,3 @@ m
 n
 o
 p
-q

test/other/metadce/test_metadce_files_wasmfs.size

@@ -1 +1 @@
-52326
+51645