breaking: std.os read/write functions + sendfile

 * rework os.sendfile and add macosx support, and a fallback
   implementation for any OS.
 * fix sendto compile error
 * std.os write functions support partial writes. closes #3443.
 * std.os pread / pwrite functions can now return `error.Unseekable`.
 * std.fs.File read/write functions now have readAll/writeAll variants
   which loop to complete operations even when partial reads/writes
   happen.
 * Audit std.os read/write functions with respect to Linux returning
   EINVAL for lengths greater than 0x7fff0000.
 * std.os read/write shim functions do not unnecessarily loop. Since
   partial reads/writes are part of the API, the caller will be forced
   to loop anyway, and so that would just be code bloat.
 * Improve doc comments
 * Add a non-trivial test for std.os.sendfile
 * Fix std.os.pread on 32 bit Linux
 * Add missing SYS_sendfile bit on aarch64

1 files changed, 12 insertions, 10 deletions

diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index 80ba5a79b5..e62f15d59a 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -236,7 +236,8 @@ pub const Loop = struct {
                 var extra_thread_index: usize = 0;
                 errdefer {
                     // writing 8 bytes to an eventfd cannot fail
-                    noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    const amt = noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    assert(amt == wakeup_bytes.len);
                     while (extra_thread_index != 0) {
                         extra_thread_index -= 1;
                         self.extra_threads[extra_thread_index].wait();
@@ -682,7 +683,8 @@ pub const Loop = struct {
                 .linux => {
                     self.posixFsRequest(&self.os_data.fs_end_request);
                     // writing 8 bytes to an eventfd cannot fail
-                    noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    const amt = noasync os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                    assert(amt == wakeup_bytes.len);
                     return;
                 },
                 .macosx, .freebsd, .netbsd, .dragonfly => {
@@ -831,7 +833,7 @@ pub const Loop = struct {
 
     /// Performs an async `os.write` using a separate thread.
     /// `fd` must block and not return EAGAIN.
-    pub fn write(self: *Loop, fd: os.fd_t, bytes: []const u8) os.WriteError!void {
+    pub fn write(self: *Loop, fd: os.fd_t, bytes: []const u8) os.WriteError!usize {
         var req_node = Request.Node{
             .data = .{
                 .msg = .{
@@ -852,7 +854,7 @@ pub const Loop = struct {
 
     /// Performs an async `os.writev` using a separate thread.
     /// `fd` must block and not return EAGAIN.
-    pub fn writev(self: *Loop, fd: os.fd_t, iov: []const os.iovec_const) os.WriteError!void {
+    pub fn writev(self: *Loop, fd: os.fd_t, iov: []const os.iovec_const) os.WriteError!usize {
         var req_node = Request.Node{
             .data = .{
                 .msg = .{
@@ -873,7 +875,7 @@ pub const Loop = struct {
 
     /// Performs an async `os.pwritev` using a separate thread.
     /// `fd` must block and not return EAGAIN.
-    pub fn pwritev(self: *Loop, fd: os.fd_t, iov: []const os.iovec_const, offset: u64) os.WriteError!void {
+    pub fn pwritev(self: *Loop, fd: os.fd_t, iov: []const os.iovec_const, offset: u64) os.WriteError!usize {
         var req_node = Request.Node{
             .data = .{
                 .msg = .{
@@ -1137,7 +1139,7 @@ pub const Loop = struct {
             pub const Write = struct {
                 fd: os.fd_t,
                 bytes: []const u8,
-                result: Error!void,
+                result: Error!usize,
 
                 pub const Error = os.WriteError;
             };
@@ -1145,7 +1147,7 @@ pub const Loop = struct {
             pub const WriteV = struct {
                 fd: os.fd_t,
                 iov: []const os.iovec_const,
-                result: Error!void,
+                result: Error!usize,
 
                 pub const Error = os.WriteError;
             };
@@ -1154,9 +1156,9 @@ pub const Loop = struct {
                 fd: os.fd_t,
                 iov: []const os.iovec_const,
                 offset: usize,
-                result: Error!void,
+                result: Error!usize,
 
-                pub const Error = os.WriteError;
+                pub const Error = os.PWriteError;
             };
 
             pub const PReadV = struct {
@@ -1165,7 +1167,7 @@ pub const Loop = struct {
                 offset: usize,
                 result: Error!usize,
 
-                pub const Error = os.ReadError;
+                pub const Error = os.PReadError;
             };
 
             pub const Open = struct {