Address review comments & fix compilation errors

lib/std/fs.zig

@@ -2270,14 +2270,14 @@ const CopyFileError = error{SystemResources} || os.CopyFileRangeError || os.Send
 fn copy_file(fd_in: os.fd_t, fd_out: os.fd_t) CopyFileError!void {
     if (comptime std.Target.current.isDarwin()) {
         const rc = os.system.fcopyfile(fd_in, fd_out, null, os.system.COPYFILE_DATA);
-        switch (errno(rc)) {
+        switch (os.errno(rc)) {
             0 => return,
-            EINVAL => unreachable,
+            os.EINVAL => unreachable,
-            ENOMEM => return error.SystemResources,
+            os.ENOMEM => return error.SystemResources,
-            // The source file was not a directory, symbolic link, or regular file.
+            // The source file is not a directory, symbolic link, or regular file.
             // Try with the fallback path before giving up.
-            ENOTSUP => {},
+            os.ENOTSUP => {},
-            else => |err| return unexpectedErrno(err),
+            else => |err| return os.unexpectedErrno(err),
         }
     }
 
@@ -2286,9 +2286,9 @@ fn copy_file(fd_in: os.fd_t, fd_out: os.fd_t) CopyFileError!void {
         // most efficient method (if available).
         var offset: u64 = 0;
         cfr_loop: while (true) {
-            // The kernel checks `offset+count` for overflow, use a 32 bit
+            // The kernel checks the u64 value `offset+count` for overflow, use
-            // value so that the syscall won't return EINVAL except for
+            // a 32 bit value so that the syscall won't return EINVAL except for
-            // impossibly large files.
+            // impossibly large files (> 2^64-1 - 2^32-1).
             const amt = try os.copy_file_range(fd_in, offset, fd_out, offset, math.maxInt(u32), 0);
             // Terminate when no data was copied
             if (amt == 0) break :cfr_loop;

lib/std/os.zig

@@ -4954,6 +4954,11 @@ pub const CopyFileRangeError = error{
     FileBusy,
 } || PReadError || PWriteError || UnexpectedError;
 
+var has_copy_file_range_syscall = init: {
+    const kernel_has_syscall = comptime std.Target.current.os.isAtLeast(.linux, .{ .major = 4, .minor = 5 }) orelse true;
+    break :init std.atomic.Int(bool).init(kernel_has_syscall);
+};
+
 /// Transfer data between file descriptors at specified offsets.
 /// Returns the number of bytes written, which can less than requested.
 ///
@@ -4979,16 +4984,11 @@ pub const CopyFileRangeError = error{
 /// Other systems fall back to calling `pread` / `pwrite`.
 ///
 /// Maximum offsets on Linux are `math.maxInt(i64)`.
-var has_copy_file_range_syscall = init: {
-    const kernel_has_syscall = comptime std.Target.current.os.isAtLeast(.linux, .{ .major = 4, .minor = 5 }) orelse true;
-    break :init std.atomic.Int(u1).init(@boolToInt(kernel_has_syscall));
-};
-
 pub fn copy_file_range(fd_in: fd_t, off_in: u64, fd_out: fd_t, off_out: u64, len: usize, flags: u32) CopyFileRangeError!usize {
     const use_c = std.c.versionCheck(.{ .major = 2, .minor = 27, .patch = 0 }).ok;
 
     if (std.Target.current.os.tag == .linux and
-        (use_c or has_copy_file_range_syscall.get() != 0))
+        (use_c or has_copy_file_range_syscall.get()))
     {
         const sys = if (use_c) std.c else linux;
 
@@ -5013,7 +5013,7 @@ pub fn copy_file_range(fd_in: fd_t, off_in: u64, fd_out: fd_t, off_out: u64, len
             EXDEV => {},
             // syscall added in Linux 4.5, use fallback
             ENOSYS => {
-                has_copy_file_range_syscall.set(0);
+                has_copy_file_range_syscall.set(false);
             },
             else => |err| return unexpectedErrno(err),
         }