osdc/Striper: add get_file_offset function

This commit adds a get_file_offset translating (object_no, object_off) -> file_offset.
This is useful for encryption object dispatch layer in librbd
to comply with disk-encryption standards that require the file offset as input.

Signed-off-by: Or Ozeri <oro@il.ibm.com>

3 files changed, 38 insertions, 0 deletions

diff --git a/src/osdc/Striper.cc b/src/osdc/Striper.cc
index 7510ac946c3..2c7f0a96087 100644
--- a/src/osdc/Striper.cc
+++ b/src/osdc/Striper.cc
@@ -296,6 +296,26 @@ uint64_t Striper::get_num_objects(const file_layout_t& layout,
   return num_periods * stripe_count - remainder_objs;
 }
 
+uint64_t Striper::get_file_offset(CephContext *cct,
+        const file_layout_t *layout, uint64_t objectno, uint64_t off) {
+  ldout(cct, 10) << "get_file_offset " << objectno << " " << off  << dendl;
+
+  __u32 object_size = layout->object_size;
+  __u32 su = layout->stripe_unit;
+  __u32 stripe_count = layout->stripe_count;
+  ceph_assert(object_size >= su);
+  uint64_t stripes_per_object = object_size / su;
+  ldout(cct, 20) << " stripes_per_object " << stripes_per_object << dendl;
+
+  uint64_t off_in_block = off % su;
+
+  uint64_t stripepos = objectno % stripe_count;
+  uint64_t objectsetno = objectno / stripe_count;
+  uint64_t stripeno = off / su + objectsetno * stripes_per_object;
+  uint64_t blockno = stripeno * stripe_count + stripepos;
+  return blockno * su + off_in_block;
+}
+
 // StripedReadResult
 
 void Striper::StripedReadResult::add_partial_result(
diff --git a/src/osdc/Striper.h b/src/osdc/Striper.h
index ddfb2c570ed..2ebc29a1213 100644
--- a/src/osdc/Striper.h
+++ b/src/osdc/Striper.h
@@ -73,6 +73,9 @@
 
     static uint64_t get_num_objects(const file_layout_t& layout,
 				    uint64_t size);
+
+    static uint64_t get_file_offset(CephContext *cct,
+            const file_layout_t *layout, uint64_t objectno, uint64_t off);
     /*
      * helper to assemble a striped result
      */
diff --git a/src/test/test_striper.cc b/src/test/test_striper.cc
index 200c2279ded..c294d646820 100644
--- a/src/test/test_striper.cc
+++ b/src/test/test_striper.cc
@@ -70,3 +70,18 @@ TEST(Striper, GetNumObj)
   numobjs = Striper::get_num_objects(l, size);
   ASSERT_EQ(6u, numobjs);
 }
+
+TEST(Striper, GetFileOffset)
+{
+  file_layout_t l;
+
+  l.object_size = 262144;
+  l.stripe_unit = 4096;
+  l.stripe_count = 3;
+
+  uint64_t object_no = 100;
+  uint64_t object_off = 200000;
+  uint64_t file_offset = Striper::get_file_offset(
+          g_ceph_context, &l, object_no, object_off);
+  ASSERT_EQ(26549568u, file_offset);
+}