Add the ability for backends to specify

Signed-off-by: Tushar Gohad <tushar.gohad@intel.com>

include/erasurecode/erasurecode_backend.h

@@ -106,6 +106,10 @@ struct ec_backend_common {
     char                        soversion[MAX_LEN]; /* EC backend shared library version */
 
     struct ec_backend_op_stubs  *ops;               /* EC backend stubs */
+    int                         metadata_adder;     /* EC backend custom metadata adder -
+                                                     * metadata_adder bytes are added to
+                                                     * the fragment size when allocating
+                                                     * data/parity fragment buffers */
 };
 
 /* EC backend definition */

src/backends/isa-l/isa_l_vand.c

@@ -588,4 +588,5 @@ struct ec_backend_common backend_isa_l_rs_vand = {
 #endif
     .soversion                  = "2.0",
     .ops                        = &isa_l_rs_vand_op_stubs,
+    .metadata_adder             = 0,
 };

src/backends/jerasure/jerasure_rs_cauchy.c

@@ -384,4 +384,5 @@ struct ec_backend_common backend_jerasure_rs_cauchy = {
 #endif
     .soversion                  = "2.0",
     .ops                        = &jerasure_rs_cauchy_op_stubs,
+    .metadata_adder             = 0,
 };

src/backends/jerasure/jerasure_rs_vand.c

@@ -325,4 +325,5 @@ struct ec_backend_common backend_jerasure_rs_vand = {
 #endif
     .soversion                  = "2.0",
     .ops                        = &jerasure_rs_vand_op_stubs,
+    .metadata_adder             = 0,
 };

src/backends/null/null.c

@@ -223,5 +223,6 @@ struct ec_backend_common backend_null = {
 #endif
     .soversion                  = "1.0",
     .ops                        = &null_op_stubs,
+    .metadata_adder             = 0,
 };
 

src/backends/xor/flat_xor_hd.c

@@ -170,5 +170,6 @@ struct ec_backend_common backend_flat_xor_hd = {
 #endif
     .soversion                  = "1.0",
     .ops                        = &flat_xor_hd_op_stubs,
+    .metadata_adder             = 0,
 };
 

src/erasurecode_helpers.c

@@ -175,6 +175,9 @@ int get_aligned_data_size(ec_backend_t instance, int data_len)
     int alignment_multiple;
     int aligned_size = 0;
 
+    /* Account for any custom metadata the backend wants to add in data_len */
+    data_len += instance->common.metadata_adder;
+
     /*
      * For Cauchy reed-solomon align to k*word_size*packet_size
      * For Vandermonde reed-solomon and flat-XOR, align to k*word_size