Base: WritePlatformFile now retries the operation if

the OS writes less than expected (for POSIX).

BUG=94161
TEST=none
Review URL: http://codereview.chromium.org/7745008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@98497 0039d316-1c4b-4281-b951-d872f2087c98

base/platform_file.h

@@ -123,7 +123,8 @@ BASE_EXPORT int ReadPlatformFile(PlatformFile file, int64 offset,
 
 // Writes the given buffer into the file at the given offset, overwritting any
 // data that was previously there. Returns the number of bytes written, or -1
-// on error.
+// on error. Note that this function makes a best effort to write all data on
+// all platforms.
 BASE_EXPORT int WritePlatformFile(PlatformFile file, int64 offset,
                                   const char* data, int size);
 

base/platform_file_posix.cc

@@ -155,10 +155,21 @@ int ReadPlatformFile(PlatformFile file, int64 offset, char* data, int size) {
 
 int WritePlatformFile(PlatformFile file, int64 offset,
                       const char* data, int size) {
-  if (file < 0)
+  if (file < 0 || size < 0)
     return -1;
 
-  return HANDLE_EINTR(pwrite(file, data, size, offset));
+  int bytes_written = 0;
+  int rv;
+  do {
+    rv = HANDLE_EINTR(pwrite(file, data + bytes_written,
+                             size - bytes_written, offset + bytes_written));
+    if (rv <= 0)
+      break;
+
+    bytes_written += rv;
+  } while (bytes_written < size);
+
+  return bytes_written ? bytes_written : rv;
 }
 
 bool TruncatePlatformFile(PlatformFile file, int64 length) {

base/platform_file_unittest.cc

@@ -37,23 +37,7 @@ int ReadFully(base::PlatformFile file, int64 offset, char* data, int size) {
 // Returns the number of bytes written.
 int WriteFully(base::PlatformFile file, int64 offset,
                const char* data, int size) {
-  int total_bytes_written = 0;
-  int bytes_written;
-  while (total_bytes_written < size) {
-    bytes_written = base::WritePlatformFile(
-        file, offset + total_bytes_written, &data[total_bytes_written],
-        size - total_bytes_written);
-
-    if ((bytes_written == 0) && (size == 0))
-      return 0;
-
-    if ((bytes_written <= 0) || (bytes_written > size - total_bytes_written))
-      return -1;
-
-    total_bytes_written += bytes_written;
-  }
-
-  return total_bytes_written;
+  return base::WritePlatformFile(file, offset, data, size);
 }
 
 } // namespace