wasip3: Get pread/pwrite working (WebAssembly#759)

This is different than wasip2 so needed some custom implementations.

---------

Co-authored-by: Joel Dice <joel.dice@akamai.com>

Author: alexcrichton

libc-bottom-half/cloudlibc/src/libc/unistd/pread.c

@@ -12,6 +12,10 @@
 #include <common/errors.h>
 #endif
 
+#ifdef __wasip3__
+#include <wasi/wasip3_block.h>
+#endif
+
 ssize_t pread(int fildes, void *buf, size_t nbyte, off_t offset) {
   if (offset < 0) {
     errno = EINVAL;
@@ -66,12 +70,38 @@ ssize_t pread(int fildes, void *buf, size_t nbyte, off_t offset) {
 
   return bytes_read;
 #elif defined(__wasip3__)
-  (void) fildes;
-  (void) buf;
-  (void) nbyte;
-  // TODO(wasip3)
-  errno = ENOTSUP;
-  return -1;
+  filesystem_borrow_descriptor_t file_handle;
+  if (fd_to_file_handle(fildes, &file_handle) < 0)
+    return -1;
+
+  // Use `read-via-stream` to acquire a stream of data at this specified file
+  // offset, then issue a read and wait for it to finish.
+  filesystem_tuple2_stream_u8_future_result_void_error_code_t io;
+  filesystem_method_descriptor_read_via_stream(file_handle, offset, &io);
+  bool closed;
+  size_t ret = __wasilibc_stream_block_on(
+    filesystem_stream_u8_read(io.f0, buf, nbyte),
+    io.f0,
+    &closed);
+  filesystem_stream_u8_drop_readable(io.f0);
+
+  // If zero bytes were read then read the provided future to see
+  // what happened. Otherwise close the future as we won't be reading the
+  // result.
+  if (ret == 0) {
+    filesystem_result_void_error_code_t result;
+    __wasilibc_future_block_on(
+      filesystem_future_result_void_error_code_read(io.f1, &result),
+      io.f1);
+    filesystem_future_result_void_error_code_drop_readable(io.f1);
+    if (result.is_err) {
+      translate_error(result.val.err);
+      return -1;
+    }
+  } else {
+    filesystem_future_result_void_error_code_drop_readable(io.f1);
+  }
+  return ret;
 #else
 # error "Unknown WASI version"
 #endif

libc-bottom-half/cloudlibc/src/libc/unistd/pwrite.c

@@ -11,6 +11,10 @@
 #include <common/errors.h>
 #endif
 
+#ifdef __wasip3__
+#include <wasi/wasip3_block.h>
+#endif
+
 ssize_t pwrite(int fildes, const void *buf, size_t nbyte, off_t offset) {
   if (offset < 0) {
     errno = EINVAL;
@@ -62,12 +66,34 @@ ssize_t pwrite(int fildes, const void *buf, size_t nbyte, off_t offset) {
 
   return bytes_written;
 #elif defined(__wasip3__)
-  (void) fildes;
-  (void) buf;
-  (void) nbyte;
-  // TODO(wasip3)
-  errno = ENOTSUP;
-  return -1;
+  filesystem_borrow_descriptor_t file_handle;
+  if (fd_to_file_handle(fildes, &file_handle) < 0)
+    return -1;
+
+  // Create a read/write stream, use `write-via-stream` to start writing,
+  // then perform the write to see how much was accepted.
+  filesystem_stream_u8_writer_t writer;
+  filesystem_stream_u8_t reader = filesystem_stream_u8_new(&writer);
+  filesystem_result_void_error_code_t result;
+  wasip3_subtask_status_t subtask_status =
+    filesystem_method_descriptor_write_via_stream(file_handle, reader, offset, &result);
+  bool closed;
+  size_t ret = __wasilibc_stream_block_on(
+    filesystem_stream_u8_write(writer, buf, nbyte),
+    writer,
+    &closed);
+  filesystem_stream_u8_drop_writable(writer);
+
+  // Wait for the subtask to resolve now that the writer half is closed and if
+  // we failed to write bytes (0 bytes written) and the result is an error we
+  // can return -1.
+  if (WASIP3_SUBTASK_STATE(subtask_status) != WASIP3_SUBTASK_RETURNED)
+    __wasilibc_subtask_block_on_and_drop(WASIP3_SUBTASK_HANDLE(subtask_status));
+  if (ret == 0 && result.is_err) {
+    translate_error(result.val.err);
+    return -1;
+  }
+  return ret;
 #else
 # error "Unsupported WASI version"
 #endif

test/CMakeLists.txt

@@ -290,8 +290,8 @@ add_wasilibc_test(memcmp.c LDFLAGS -Wl,--stack-first -Wl,--initial-memory=327680
 add_wasilibc_test(opendir.c FS ARGV /)
 add_wasilibc_test(open_relative_path.c FS ARGV /)
 add_wasilibc_test(poll.c FS FAILP3)
-add_wasilibc_test(preadvwritev.c FS FAILP3)
-add_wasilibc_test(preadwrite.c FS FAILP3)
+add_wasilibc_test(preadvwritev.c FS)
+add_wasilibc_test(preadwrite.c FS)
 add_wasilibc_test(readlink.c FS)
 add_wasilibc_test(readv.c FS)
 add_wasilibc_test(rename.c FS)

test/src/sleep.c

@@ -20,8 +20,8 @@
 #endif
 
 int main(void) {
-  // Sleep for a total of 2 seconds
-  unsigned int seconds_to_sleep = 2;
+  // Sleep for a total of 1 second
+  unsigned int seconds_to_sleep = 1;
 
   struct timespec start_time, end_time;
   clock_gettime(CLOCK, &start_time);