copy_file_range linux syscall (#6010)

lib/std/builtin.zig

@@ -447,6 +447,14 @@ pub const Version = struct {
             if (self.max.order(ver) == .lt) return false;
             return true;
         }
+
+        /// Checks if system is guaranteed to be at least `version` or older than `version`.
+        /// Returns `null` if a runtime check is required.
+        pub fn isAtLeast(self: Range, ver: Version) ?bool {
+            if (self.min.order(ver) != .lt) return true;
+            if (self.max.order(ver) == .lt) return false;
+            return null;
+        }
     };
 
     pub fn order(lhs: Version, rhs: Version) std.math.Order {

lib/std/c/linux.zig

@@ -91,6 +91,8 @@ pub extern "c" fn sendfile(
     count: usize,
 ) isize;
 
+pub extern "c" fn copy_file_range(fd_in: fd_t, off_in: ?*i64, fd_out: fd_t, off_out: ?*i64, len: usize, flags: c_uint) isize;
+
 pub const pthread_attr_t = extern struct {
     __size: [56]u8,
     __align: c_long,

lib/std/fs/file.zig

@@ -607,15 +607,10 @@ pub const File = struct {
         }
     }
 
-    pub const CopyRangeError = PWriteError || PReadError;
+    pub const CopyRangeError = os.CopyFileRangeError;
 
     pub fn copyRange(in: File, in_offset: u64, out: File, out_offset: u64, len: usize) CopyRangeError!usize {
-        // TODO take advantage of copy_file_range OS APIs
-        var buf: [8 * 4096]u8 = undefined;
-        const adjusted_count = math.min(buf.len, len);
-        const amt_read = try in.pread(buf[0..adjusted_count], in_offset);
-        if (amt_read == 0) return @as(usize, 0);
-        return out.pwrite(buf[0..amt_read], out_offset);
+        return os.copy_file_range(in.handle, in_offset, out.handle, out_offset, len, 0);
     }
 
     /// Returns the number of bytes copied. If the number read is smaller than `buffer.len`, it

lib/std/fs/test.zig

@@ -328,6 +328,32 @@ test "sendfile" {
     testing.expect(mem.eql(u8, written_buf[0..amt], "header1\nsecond header\nine1\nsecontrailer1\nsecond trailer\n"));
 }
 
+test "copyRangeAll" {
+    var tmp = tmpDir(.{});
+    defer tmp.cleanup();
+
+    try tmp.dir.makePath("os_test_tmp");
+    defer tmp.dir.deleteTree("os_test_tmp") catch {};
+
+    var dir = try tmp.dir.openDir("os_test_tmp", .{});
+    defer dir.close();
+
+    var src_file = try dir.createFile("file1.txt", .{ .read = true });
+    defer src_file.close();
+
+    const data = "u6wj+JmdF3qHsFPE BUlH2g4gJCmEz0PP";
+    try src_file.writeAll(data);
+
+    var dest_file = try dir.createFile("file2.txt", .{ .read = true });
+    defer dest_file.close();
+
+    var written_buf: [100]u8 = undefined;
+    _ = try src_file.copyRangeAll(0, dest_file, 0, data.len);
+
+    const amt = try dest_file.preadAll(&written_buf, 0);
+    testing.expect(mem.eql(u8, written_buf[0..amt], data));
+}
+
 test "fs.copyFile" {
     const data = "u6wj+JmdF3qHsFPE BUlH2g4gJCmEz0PP";
     const src_file = "tmp_test_copy_file.txt";

lib/std/os.zig

@@ -4926,6 +4926,85 @@ pub fn sendfile(
     return total_written;
 }
 
+pub const CopyFileRangeError = error{
+    FileTooBig,
+    InputOutput,
+    IsDir,
+    OutOfMemory,
+    NoSpaceLeft,
+    Unseekable,
+    PermissionDenied,
+    FileBusy,
+} || PReadError || PWriteError || UnexpectedError;
+
+/// Transfer data between file descriptors at specified offsets.
+/// Returns the number of bytes written, which can less than requested.
+///
+/// The `copy_file_range` call copies `len` bytes from one file descriptor to another. When possible,
+/// this is done within the operating system kernel, which can provide better performance
+/// characteristics than transferring data from kernel to user space and back, such as with
+/// `pread` and `pwrite` calls.
+///
+/// `fd_in` must be a file descriptor opened for reading, and `fd_out` must be a file descriptor
+/// opened for writing. They may be any kind of file descriptor; however, if `fd_in` is not a regular
+/// file system file, it may cause this function to fall back to calling `pread` and `pwrite`, in which case
+/// atomicity guarantees no longer apply.
+///
+/// If `fd_in` and `fd_out` are the same, source and target ranges must not overlap.
+/// The file descriptor seek positions are ignored and not updated.
+/// When `off_in` is past the end of the input file, it successfully reads 0 bytes.
+///
+/// `flags` has different meanings per operating system; refer to the respective man pages.
+///
+/// These systems support in-kernel data copying:
+/// * Linux 4.5 (cross-filesystem 5.3)
+///
+/// Other systems fall back to calling `pread` / `pwrite`.
+///
+/// Maximum offsets on Linux are `math.maxInt(i64)`.
+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;
+
+    // TODO support for other systems than linux
+    const try_syscall = comptime std.Target.current.os.isAtLeast(.linux, .{ .major = 4, .minor = 5 }) != false;
+
+    if (use_c or try_syscall) {
+        const sys = if (use_c) std.c else linux;
+
+        var off_in_copy = @bitCast(i64, off_in);
+        var off_out_copy = @bitCast(i64, off_out);
+
+        const rc = sys.copy_file_range(fd_in, &off_in_copy, fd_out, &off_out_copy, len, flags);
+
+        // TODO avoid wasting a syscall every time if kernel is too old and returns ENOSYS https://github.com/ziglang/zig/issues/1018
+
+        switch (sys.getErrno(rc)) {
+            0 => return @intCast(usize, rc),
+            EBADF => unreachable,
+            EFBIG => return error.FileTooBig,
+            EIO => return error.InputOutput,
+            EISDIR => return error.IsDir,
+            ENOMEM => return error.OutOfMemory,
+            ENOSPC => return error.NoSpaceLeft,
+            EOVERFLOW => return error.Unseekable,
+            EPERM => return error.PermissionDenied,
+            ETXTBSY => return error.FileBusy,
+            EINVAL => {}, // these may not be regular files, try fallback
+            EXDEV => {}, // support for cross-filesystem copy added in Linux 5.3, use fallback
+            ENOSYS => {}, // syscall added in Linux 4.5, use fallback
+            else => |err| return unexpectedErrno(err),
+        }
+    }
+
+    var buf: [8 * 4096]u8 = undefined;
+    const adjusted_count = math.min(buf.len, len);
+    const amt_read = try pread(fd_in, buf[0..adjusted_count], off_in);
+    // TODO without @as the line below fails to compile for wasm32-wasi:
+    // error: integer value 0 cannot be coerced to type 'os.PWriteError!usize'
+    if (amt_read == 0) return @as(usize, 0);
+    return pwrite(fd_out, buf[0..amt_read], off_out);
+}
+
 pub const PollError = error{
     /// The kernel had no space to allocate file descriptor tables.
     SystemResources,

lib/std/os/linux.zig

@@ -1210,6 +1210,18 @@ pub fn signalfd4(fd: fd_t, mask: *const sigset_t, flags: i32) usize {
     );
 }
 
+pub fn copy_file_range(fd_in: fd_t, off_in: ?*i64, fd_out: fd_t, off_out: ?*i64, len: usize, flags: u32) usize {
+    return syscall6(
+        .copy_file_range,
+        @bitCast(usize, @as(isize, fd_in)),
+        @ptrToInt(off_in),
+        @bitCast(usize, @as(isize, fd_out)),
+        @ptrToInt(off_out),
+        len,
+        flags,
+    );
+}
+
 test "" {
     if (builtin.os.tag == .linux) {
         _ = @import("linux/test.zig");

lib/std/target.zig

@@ -100,6 +100,14 @@ pub const Target = struct {
                 pub fn includesVersion(self: Range, ver: WindowsVersion) bool {
                     return @enumToInt(ver) >= @enumToInt(self.min) and @enumToInt(ver) <= @enumToInt(self.max);
                 }
+
+                /// Checks if system is guaranteed to be at least `version` or older than `version`.
+                /// Returns `null` if a runtime check is required.
+                pub fn isAtLeast(self: Range, ver: WindowsVersion) ?bool {
+                    if (@enumToInt(self.min) >= @enumToInt(ver)) return true;
+                    if (@enumToInt(self.max) < @enumToInt(ver)) return false;
+                    return null;
+                }
             };
 
             /// This function is defined to serialize a Zig source code representation of this
@@ -135,6 +143,12 @@ pub const Target = struct {
             pub fn includesVersion(self: LinuxVersionRange, ver: Version) bool {
                 return self.range.includesVersion(ver);
             }
+
+            /// Checks if system is guaranteed to be at least `version` or older than `version`.
+            /// Returns `null` if a runtime check is required.
+            pub fn isAtLeast(self: LinuxVersionRange, ver: Version) ?bool {
+                return self.range.isAtLeast(ver);
+            }
         };
 
         /// The version ranges here represent the minimum OS version to be supported
@@ -158,6 +172,8 @@ pub const Target = struct {
         ///
         /// Binaries built with a given maximum version will continue to function on newer operating system
         /// versions. However, such a binary may not take full advantage of the newer operating system APIs.
+        ///
+        /// See `Os.isAtLeast`.
         pub const VersionRange = union {
             none: void,
             semver: Version.Range,
@@ -273,6 +289,18 @@ pub const Target = struct {
             };
         }
 
+        /// Checks if system is guaranteed to be at least `version` or older than `version`.
+        /// Returns `null` if a runtime check is required.
+        pub fn isAtLeast(self: Os, comptime tag: Tag, version: anytype) ?bool {
+            if (self.tag != tag) return false;
+
+            return switch (tag) {
+                .linux => self.version_range.linux.isAtLeast(version),
+                .windows => self.version_range.windows.isAtLeast(version),
+                else => self.version_range.semver.isAtLeast(version),
+            };
+        }
+
         pub fn requiresLibC(os: Os) bool {
             return switch (os.tag) {
                 .freebsd,