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

content/common/font_config_ipc_linux.cc

Index: content/common/font_config_ipc_linux.cc
===================================================================
--- content/common/font_config_ipc_linux.cc	(revision 188729)
+++ content/common/font_config_ipc_linux.cc	(working copy)
@@ -6,10 +6,13 @@
 
 #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/file_util.h"
 #include "base/pickle.h"
 #include "base/posix/unix_domain_socket_linux.h"
 #include "skia/ext/skia_utils_base.h"
@@ -17,6 +20,66 @@
 
 namespace content {
 
+// Takes "ownership" of the file descriptor, and will close() it.
+class SkFileDescriptorStream : public SkStream {

[jln (very slow on Chromium), 2013/03/18 18:25:37]

General nit: why are you using a 4 spaces indent?

[reed1, 2013/03/18 18:42:35]

Done.

+  public:
+    SkFileDescriptorStream(int fd) {
+        memory_ = NULL;

[jln (very slow on Chromium), 2013/03/18 18:25:37]

You don't want to use an initialization list instead?

[reed1, 2013/03/18 18:42:35]

Done.

+        offset_ = 0;
+
+        // this ensures that if we fail in the constructor, we will safely

[jln (very slow on Chromium), 2013/03/18 18:25:37]

Nit: s/this/This

[reed1, 2013/03/18 18:42:35]

Done.

+        // ignore all subsequent calls to read() because we will always trim

[jln (very slow on Chromium), 2013/03/18 18:25:37]

I don't think this currently works. You just do remaining = length_ - offset_,
with remaining being unsigned.

If you don't want to have an explicit Init() method, make everything very clear
by having a bool initialized_ and adding a CHECK() for it in your methods maybe?

+        // the requested size down to 0

[jln (very slow on Chromium), 2013/03/18 18:25:37]

Nit: final "."

[reed1, 2013/03/18 18:42:35]

Done.

+        length_ = 0;
+
+        struct stat st;
+        if (fstat(fd, &st))

[jln (very slow on Chromium), 2013/03/18 18:25:37]

close the fd here as well ?

[reed1, 2013/03/18 18:42:35]

Done.

+            return;
+
+        void* memory = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, fd, 0);
+        DCHECK(!HANDLE_EINTR(close(fd)));
+        if (memory == MAP_FAILED)
+            return;
+
+        memory_ = reinterpret_cast<uint8_t*>(memory);
+        length_ = st.st_size;
+    }
+
+    virtual ~SkFileDescriptorStream() {

[jln (very slow on Chromium), 2013/03/18 18:25:37]

This works, because length == 0 will make the kernel EINVAL, but wouldn't it be
nicer to if (!memory_) ?

Also I would at least DCHECK it to catch bugs.

[reed1, 2013/03/18 18:42:35]

Done.

+        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)

[jln (very slow on Chromium), 2013/03/18 18:25:37]

Shouldn't we just CHECK buffer at the start of this function or here ?

[reed1, 2013/03/18 18:42:35]

buffer == NULL is defined to mean "skip", so it is valid for it to be null.

+            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) {
 }
@@ -97,7 +160,7 @@
     return NULL;
   }
 
-  return new SkFDStream(result_fd, true);
+  return new SkFileDescriptorStream(result_fd);
 }
 
 }  // namespace content