commit a5450a983e032bddffe77a4092a74c7a1571e6cd
author Brian Silverman <bsilver16384@gmail.com> Wed Aug 12 19:59:57 2020 -0700
committer Brian Silverman <bsilver16384@gmail.com> Fri Aug 14 17:06:29 2020 -0700
tree 7fdb772e0004095296331999c2b419308d3159c6
parent 4e33091cd5bf6972ac0979523e88e990dde7a28f

Use a read-only mapping for reading from shared memory

This makes it a lot harder for readers to accidentally write.

Change-Id: I29025f37b0767825e57314cc1221510fd9455b55

aos/events/shm_event_loop.h

diff --git a/aos/events/shm_event_loop.h b/aos/events/shm_event_loop.h
index d7ea5e6..8dabcb5 100644
--- a/aos/events/shm_event_loop.h
+++ b/aos/events/shm_event_loop.h
@@ -83,7 +83,7 @@
   // Returns the local mapping of the shared memory used by the watcher on the
   // specified channel. A watcher must be created on this channel before calling
   // this.
-  absl::Span<char> GetWatcherSharedMemory(const Channel *channel);
+  absl::Span<const char> GetWatcherSharedMemory(const Channel *channel);
 
   // Returns the local mapping of the shared memory used by the provided Sender.
   template <typename T>
@@ -93,8 +93,12 @@
 
   // Returns the local mapping of the private memory used by the provided
   // Fetcher to hold messages.
+  //
+  // Note that this may be the entire shared memory region held by this fetcher,
+  // depending on its channel's read_method.
   template <typename T>
-  absl::Span<char> GetFetcherPrivateMemory(aos::Fetcher<T> *fetcher) const {
+  absl::Span<const char> GetFetcherPrivateMemory(
+      aos::Fetcher<T> *fetcher) const {
     return GetShmFetcherPrivateMemory(GetRawFetcher(fetcher));
   }
 
@@ -127,7 +131,7 @@
   absl::Span<char> GetShmSenderSharedMemory(const aos::RawSender *sender) const;
 
   // Private method to access the private memory mapping of a ShmFetcher.
-  absl::Span<char> GetShmFetcherPrivateMemory(
+  absl::Span<const char> GetShmFetcherPrivateMemory(
       const aos::RawFetcher *fetcher) const;
 
   std::vector<std::function<void()>> on_run_;