buffer: add buffer::list::iterator::get_ptr_and_advance

Efficiently iterate over buffers in a list, via an iterator.

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/src/common/buffer.cc b/src/common/buffer.cc
index 3557b3775d4f81471e91596c079443b171dd58a8..baf97828091a4ad1957822ec893f00190656a84c 100644 (file)
--- a/src/common/buffer.cc
+++ b/src/common/buffer.cc
@@ -1198,6 +1198,26 @@ static simple_spinlock_t buffer_debug_lock = SIMPLE_SPINLOCK_INITIALIZER;
     }
   }
 
+  template<bool is_const>
+  size_t buffer::list::iterator_impl<is_const>::get_ptr_and_advance(
+    size_t want, const char **data)
+  {
+    if (p == ls->end()) {
+      seek(off);
+      if (p == ls->end()) {
+       return 0;
+      }
+    }
+    *data = p->c_str() + p_off;
+    size_t l = MIN(p->length() - p_off, want);
+    p_off += l;
+    if (p_off == p->length()) {
+      ++p;
+      p_off = 0;
+    }
+    return l;
+  }
+
   // explicitly instantiate only the iterator types we need, so we can hide the
   // details in this compilation unit without introducing unnecessary link time
   // dependencies.

diff --git a/src/include/buffer.h b/src/include/buffer.h
index 4c5de1d486beb2380b7e5e58cffd4e66d96e4983..9441cd583d2313dca8bcb34d99c83dfd09c06162 100644 (file)
--- a/src/include/buffer.h
+++ b/src/include/buffer.h
@@ -324,6 +324,11 @@ namespace buffer CEPH_BUFFER_API {
       void copy(unsigned len, std::string &dest);
       void copy_all(list &dest);
 
+      // get a pointer to the currenet iterator position, return the
+      // number of bytes we can read from that position (up to want),
+      // and advance the iterator by that amount.
+      size_t get_ptr_and_advance(size_t want, const char **p);
+
       friend bool operator==(const iterator_impl& lhs,
                             const iterator_impl& rhs) {
        return &lhs.get_bl() == &rhs.get_bl() && lhs.get_off() == rhs.get_off();

diff --git a/src/test/bufferlist.cc b/src/test/bufferlist.cc
index 43eb76d8362a320b77ef138488252f8e826a1bdf..0f1696f46b5bf386bcec26bbf9756f229f3905aa 100644 (file)
--- a/src/test/bufferlist.cc
+++ b/src/test/bufferlist.cc
@@ -1037,6 +1037,27 @@ TEST(BufferListIterator, advance) {
   }
 }
 
+TEST(BufferListIterator, get_ptr_and_advance)
+{
+  bufferptr a("one", 3);
+  bufferptr b("two", 3);
+  bufferptr c("three", 5);
+  bufferlist bl;
+  bl.append(a);
+  bl.append(b);
+  bl.append(c);
+  const char *ptr;
+  bufferlist::iterator p = bl.begin();
+  ASSERT_EQ(3u, p.get_ptr_and_advance(11, &ptr));
+  ASSERT_EQ(0, memcmp(ptr, "one", 3));
+  ASSERT_EQ(2u, p.get_ptr_and_advance(2, &ptr));
+  ASSERT_EQ(0, memcmp(ptr, "tw", 2));
+  ASSERT_EQ(1u, p.get_ptr_and_advance(4, &ptr));
+  ASSERT_EQ(0, memcmp(ptr, "o", 1));
+  ASSERT_EQ(5u, p.get_ptr_and_advance(5, &ptr));
+  ASSERT_EQ(0, memcmp(ptr, "three", 5));
+}
+
 TEST(BufferListIterator, seek) {
   bufferlist bl;
   bl.append("ABC", 3);