common: introduce obtain_contiguous_space() to bufferlist.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

diff --git a/src/common/buffer.cc b/src/common/buffer.cc
index 6a79d2431da72a13e2dee79e2d612f23a5947707..3c85f7492437dd3fd373fe9490aff8d99eac411f 100644 (file)
--- a/src/common/buffer.cc
+++ b/src/common/buffer.cc
@@ -1453,6 +1453,34 @@ static ceph::spinlock debug_lock;
     }
   }
 
+  buffer::list::reserve_t buffer::list::obtain_contiguous_space(
+    const unsigned len)
+  {
+    // note: if len < the normal append_buffer size it *might*
+    // be better to allocate a normal-sized append_buffer and
+    // use part of it.  however, that optimizes for the case of
+    // old-style types including new-style types.  and in most
+    // such cases, this won't be the very first thing encoded to
+    // the list, so append_buffer will already be allocated.
+    // OTOH if everything is new-style, we *should* allocate
+    // only what we need and conserve memory.
+    if (unlikely(get_append_buffer_unused_tail_length() < len)) {
+      auto new_back = \
+       buffer::ptr_node::create(buffer::create(len)).release();
+      new_back->set_length(0);   // unused, so far.
+      _buffers.push_back(*new_back);
+      _carriage = new_back;
+      return { new_back->c_str(), &new_back->_len, &_len };
+    } else {
+      if (unlikely(_carriage != &_buffers.back())) {
+        auto bptr = ptr_node::create(*_carriage, _carriage->length(), 0);
+       _carriage = bptr.get();
+       _buffers.push_back(*bptr.release());
+      }
+      return { _carriage->end_c_str(), &_carriage->_len, &_len };
+    }
+  }
+
   void buffer::list::append(const ptr& bp)
   {
       push_back(bp);

diff --git a/src/include/buffer.h b/src/include/buffer.h
index 334a594ab230fe2314d32d95844262c81d6afcf5..15ad5a025d9a2251bfaf5c3c0ce14b9b85f82418 100644 (file)
--- a/src/include/buffer.h
+++ b/src/include/buffer.h
@@ -762,6 +762,12 @@ namespace buffer CEPH_BUFFER_API {
       void copy_in(unsigned len, const list& otherl);
     };
 
+    struct reserve_t {
+      char* bp_data;
+      unsigned* bp_len;
+      unsigned* bl_len;
+    };
+
     class contiguous_appender {
       bufferlist *pbl;
       char *pos;
@@ -1209,6 +1215,8 @@ namespace buffer CEPH_BUFFER_API {
     void append_zero(unsigned len);
     void prepend_zero(unsigned len);
 
+    reserve_t obtain_contiguous_space(unsigned len);
+
     /*
      * get a char
      */