Fix some issues around the two-phase DataPipe read API.

- The ALL_OR_NONE flag was never supported by the implementation, so make it
  an error to pass it to BeginRead.
- It doesn't make sense to pass in how many bytes to read to
  BeginReadData, so correctly document this as an out-only parameter.
- Update unit tests to no longer incorrectly attempt to use ALL_OR_NONE.

Change-Id: I23031d454bc157500664224d3658650ee77d7b22
Reviewed-on: https://chromium-review.googlesource.com/562518
Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#484835}

CrOS-Libchrome-Original-Commit: 801d8de7fb0219622a9e653220a11a827ecbed8a

1 files changed, 6 insertions, 7 deletions

diff --git a/mojo/public/c/system/data_pipe.h b/mojo/public/c/system/data_pipe.h
index f51e36cb2e..aaeafcf21e 100644
--- a/mojo/public/c/system/data_pipe.h
+++ b/mojo/public/c/system/data_pipe.h
@@ -78,10 +78,9 @@ const MojoWriteDataFlags MOJO_WRITE_DATA_FLAG_ALL_OR_NONE = 1 << 0;
 //
 //   |MOJO_READ_DATA_FLAG_NONE| - No flags; default mode.
 //   |MOJO_READ_DATA_FLAG_ALL_OR_NONE| - Read (or discard) either the requested
-//        number of elements or none. NOTE: This flag is not currently supported
-//        by |MojoBeginReadData()|.
+//        number of elements or none. For use with |MojoReadData()| only.
 //   |MOJO_READ_DATA_FLAG_DISCARD| - Discard (up to) the requested number of
-//        elements.
+//        elements. For use with |MojoReadData()| only.
 //   |MOJO_READ_DATA_FLAG_QUERY| - Query the number of elements available to
 //       read. For use with |MojoReadData()| only. Mutually exclusive with
 //       |MOJO_READ_DATA_FLAG_DISCARD|, and |MOJO_READ_DATA_FLAG_ALL_OR_NONE|
@@ -309,10 +308,10 @@ MOJO_SYSTEM_EXPORT MojoResult MojoReadData(MojoHandle data_pipe_consumer_handle,
 //   |MOJO_RESULT_SHOULD_WAIT| if no data can currently be read (and the
 //       producer is still open).
 MOJO_SYSTEM_EXPORT MojoResult
-    MojoBeginReadData(MojoHandle data_pipe_consumer_handle,
-                      const void** buffer,         // Out.
-                      uint32_t* buffer_num_bytes,  // In/out.
-                      MojoReadDataFlags flags);
+MojoBeginReadData(MojoHandle data_pipe_consumer_handle,
+                  const void** buffer,         // Out.
+                  uint32_t* buffer_num_bytes,  // Out.
+                  MojoReadDataFlags flags);
 
 // Ends a two-phase read from the data pipe consumer given by
 // |data_pipe_consumer_handle| that was begun by a call to |MojoBeginReadData()|