mmap the opened file descriptor in the renderer process, close the fd in the browser process.

content/common/font_config_ipc_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/font_config_ipc_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
+#include <sys/mman.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/uio.h>
 #include <unistd.h>
 
 #include "base/pickle.h"
 #include "base/posix/unix_domain_socket_linux.h"
 #include "skia/ext/skia_utils_base.h"
 #include "third_party/skia/include/core/SkStream.h"
 
 namespace content {
 
+// Does not retain the file-descriptor (but does call mmap on it), and so
+// the caller must still take care of closing the fd.
+class SkFileDescriptorStream : public SkStream {
+  public:
+    SkFileDescriptorStream(int fd) {
+        memory_ = NULL;
+        offset_ = 0;
+
+        // this ensures that if we fail in the constructor, we will safely
+        // ignore all subsequent calls to read() because we will always trim
+        // the requested size down to 0
+        length_ = 0;
+
+        struct stat st;
+        if (fstat(fd, &st))
+            return;
+
+        void* memory = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, fd, 0);
+        if (memory == MAP_FAILED)
+            return;
+
+        memory_ = reinterpret_cast<uint8_t*>(memory);
+        length_ = st.st_size;
+    }
+
+    virtual ~SkFileDescriptorStream() {
+        munmap(const_cast<uint8_t*>(memory_), length_);
+    }
+
+    virtual bool rewind() OVERRIDE {
+        offset_ = 0;
+        return true;
+    }
+
+    // SkStream implementation.
+    virtual size_t read(void* buffer, size_t size) OVERRIDE {
+        if (!buffer && !size) {
+            // This is request for the length of the stream.
+            return length_;
+        }
+
+        size_t remaining = length_ - offset_;
+        if (size > remaining)
+            size = remaining;
+        if (buffer)
+            memcpy(buffer, memory_ + offset_, size);
+
+        offset_ += size;
+        return size;
+    }
+
+    virtual const void* getMemoryBase() OVERRIDE {
+        return memory_;
+    }
+
+  private:
+    const uint8_t* memory_;
+    size_t offset_, length_;
+};
+
 FontConfigIPC::FontConfigIPC(int fd)
     : fd_(fd) {
 }
 
 FontConfigIPC::~FontConfigIPC() {
   close(fd_);
 }
 
 bool FontConfigIPC::matchFamilyName(const char familyName[],
                                     SkTypeface::Style requestedStyle,
@@ skipping 60 matching lines @@
   Pickle reply(reinterpret_cast<char*>(reply_buf), r);
   bool result;
   PickleIterator iter(reply);
   if (!reply.ReadBool(&iter, &result) ||
       !result) {
     if (result_fd)
       close(result_fd);
     return NULL;
   }
 
-  return new SkFDStream(result_fd, true);
+  return new SkFileDescriptorStream(result_fd);

[jln (very slow on Chromium), 2013/03/18 16:07:21]

You say that the caller should close the fd, but the caller doesn't close the
fd.

DCHECK(HANDLE_EINTR(close(result_fd)));

[reed1, 2013/03/18 16:12:47]

Good point. It is not the imnmediate caller (this line) that closes it, but the
browser process that performed the open (render_sandbox_host_linux.cc:229).

 }
 
 }  // namespace content