Split big IO requests

OCF cannot allocate request map bigger than 4MiB (due to kmalloc
limitations), thus we need to split bigger IOs into series smaller
ones to reduce request map size.

Signed-off-by: Robert Baldyga <robert.baldyga@intel.com>

configure.d/1_bio_split.conf

@@ -0,0 +1,88 @@
+#!/bin/bash
+#
+# Copyright(c) 2012-2021 Intel Corporation
+# SPDX-License-Identifier: BSD-3-Clause-Clear
+#
+
+. $(dirname $3)/conf_framework
+
+check() {
+	cur_name=$(basename $2)
+	config_file_path=$1
+    if compile_module $cur_name "bio_split(NULL, 0, 0, 0);" "linux/bio.h"
+    then
+        echo $cur_name "1" >> $config_file_path
+    elif compile_module $cur_name "bio_split(NULL, 0);" "linux/bio.h"
+    then
+        echo $cur_name "2" >> $config_file_path
+    else
+        echo $cur_name "X" >> $config_file_path
+    fi
+}
+
+apply() {
+    case "$1" in
+    "1")
+        add_function "
+    static inline struct bio *cas_bio_split(struct bio *bio, int sectors)
+    {
+        return bio_split(bio, sectors, GFP_NOIO, NULL);
+    }" ;;
+    "2")
+        add_function "
+    static inline struct bio *cas_bio_split(struct bio *bio, int sectors)
+    {
+        struct bio *split, copy;
+        int bytes = sectors << 9;
+        uint32_t idx, vecs = 0;
+        int ret;
+
+        copy = *bio;
+        copy.bi_io_vec = &copy.bi_io_vec[copy.bi_idx];
+        copy.bi_vcnt -= copy.bi_idx;
+        copy.bi_idx = 0;
+
+        BUG_ON(bytes >= bio->bi_size);
+
+        // For simplicity we assume that split is alligned.
+        // Otherwise bvec modification would be required.
+        while (bytes) {
+            if (bytes >= bio_iovec_idx(&copy, vecs)->bv_len) {
+                bytes -= bio_iovec_idx(&copy, vecs)->bv_len;
+                vecs++;
+            } else {
+                vecs++;
+                break;
+            }
+        }
+
+        split = bio_alloc_bioset(GFP_NOIO, vecs, NULL);
+        if (!split)
+            return NULL;
+
+        copy.bi_max_vecs = vecs;
+        __bio_clone(split, &copy);
+        split->bi_size = sectors << 9;
+        split->bi_vcnt = vecs;
+
+        if (bio_integrity((&copy))) {
+            ret = bio_integrity_clone(split, bio, GFP_NOIO);
+            if (ret < 0) {
+                bio_put(split);
+                return NULL;
+            }
+            for (idx = 0, bytes = 0; idx < bio->bi_idx; idx++)
+                bytes += bio_iovec_idx(bio, idx)->bv_len;
+            bio_integrity_trim(split, bytes >> 9, sectors);
+        }
+
+        bio_advance(bio, split->bi_size);
+
+        return split;
+    }" ;;
+    *)
+        exit 1
+    esac
+}
+
+conf_run $@