[Fuchsia] Add SysmemBufferWriter::ReserveAndMapBuffer()

The new function will allow SysmemBufferWriter users to get direct
mapping to the buffer if they need it.

Bug: b/158033083
Change-Id: Id6aeabf415a65f859d6d0add7015a8a7868946ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2206339
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774397}

media/fuchsia/common/sysmem_buffer_writer.cc

@@ -70,16 +70,30 @@ class SysmemBufferWriter::Buffer {
     size_t bytes_to_fill = std::min(size_, data.size());
     memcpy(base_address_ + offset_, data.data(), bytes_to_fill);
 
-    // Flush CPU cache if StreamProcessor reads from RAM.
-    if (coherency_domain_ == fuchsia::sysmem::CoherencyDomain::RAM) {
-      zx_status_t status = zx_cache_flush(base_address_ + offset_,
-                                          bytes_to_fill, ZX_CACHE_FLUSH_DATA);
-      ZX_DCHECK(status == ZX_OK, status) << "zx_cache_flush";
-    }
+    FlushBuffer(0, bytes_to_fill);
 
     return bytes_to_fill;
   }
 
+  base::span<uint8_t> ReserveAndMapBuffer() {
+    DCHECK(!is_used_);
+    is_used_ = true;
+    return base::make_span(base_address_ + offset_, size_);
+  }
+
+  void FlushBuffer(size_t flush_offset, size_t flush_size) {
+    DCHECK(is_used_);
+    DCHECK_LE(flush_size, size_ - flush_offset);
+
+    if (coherency_domain_ != fuchsia::sysmem::CoherencyDomain::RAM)
+      return;
+
+    uint8_t* address = base_address_ + offset_ + flush_offset;
+    zx_status_t status =
+        zx_cache_flush(address, flush_size, ZX_CACHE_FLUSH_DATA);
+    ZX_DCHECK(status == ZX_OK, status) << "zx_cache_flush";
+  }
+
   void Release() { is_used_ = false; }
 
  private:
@@ -187,4 +201,16 @@ SysmemBufferWriter::GetRecommendedConstraints(
   return buffer_constraints;
 }
 
+base::span<uint8_t> SysmemBufferWriter::ReserveAndMapBuffer(size_t index) {
+  DCHECK_LT(index, buffers_.size());
+  return buffers_[index].ReserveAndMapBuffer();
+}
+
+void SysmemBufferWriter::FlushBuffer(size_t index,
+                                     size_t flush_offset,
+                                     size_t flush_size) {
+  DCHECK_LT(index, buffers_.size());
+  return buffers_[index].FlushBuffer(flush_offset, flush_size);
+}
+
 }  // namespace media

media/fuchsia/common/sysmem_buffer_writer.h

@@ -11,6 +11,7 @@
 #include <memory>
 
 #include "base/containers/span.h"
+#include "base/memory/shared_memory_mapping.h"
 #include "base/optional.h"
 
 namespace media {
@@ -30,11 +31,24 @@ class SysmemBufferWriter {
   explicit SysmemBufferWriter(std::vector<Buffer> buffers);
   ~SysmemBufferWriter();
 
-  // Write the content of |data| into buffer at |index|. Return num of bytes
-  // written into the buffer. Write a used buffer will fail. It will mark the
-  // buffer as "used".
+  SysmemBufferWriter(const SysmemBufferWriter&) = delete;
+  SysmemBufferWriter& operator=(const SysmemBufferWriter&) = delete;
+
+  // Write the content of |data| into the buffer at |index|. Return num of bytes
+  // written into the buffer. Can be called only for an unused buffer. Marks
+  // the buffer as used.
   size_t Write(size_t index, base::span<const uint8_t> data);
 
+  // Returns a span for the memory-mapping of the buffer with the specified
+  // |index|. Can be called only for an unused buffer. Marks the buffer as used.
+  // Callers must call FlushCache() after they are finished updating the buffer.
+  base::span<uint8_t> ReserveAndMapBuffer(size_t index);
+
+  // Flushes CPU cache for specified range in the buffer with the specified
+  // |index| in case the buffer collection uses RAM coherency. No-op for
+  // collections with RAM coherency.
+  void FlushBuffer(size_t index, size_t flush_offset, size_t flush_size);
+
   // Acquire unused buffer for write. If |min_size| is provided, the returned
   // buffer will have available size larger than |min_size|. This will NOT
   // mark the buffer as "used".
@@ -50,8 +64,6 @@ class SysmemBufferWriter {
 
  private:
   std::vector<Buffer> buffers_;
-
-  DISALLOW_COPY_AND_ASSIGN(SysmemBufferWriter);
 };
 
 }  // namespace media