Adding io.h and io_posix.c

- DAG and memo file creation will now be taken care of in libethash
  itself.

- To that end we crete a very minimal IO module for ethash.

- Depending on the target system io_posix or io_win32 will be used.

- Implemented ethash_io_prepare() for posix

CMakeLists.txt

@@ -19,6 +19,12 @@ set(FILES 	util.c
           	fnv.h
           	data_sizes.h)
 
+if (MSVC)
+	list(APPEND FILES io_win32.c)
+else()
+	list(APPEND FILES io_posix.c)
+endif()
+
 if (NOT CRYPTOPP_FOUND)
 	find_package(CryptoPP 5.6.2)
 endif()

io.h

@@ -0,0 +1,53 @@
+/*
+  This file is part of ethash.
+
+  ethash is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  ethash is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with ethash.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/** @file io.h
+ * @author Lefteris Karapetsas <lefteris@ethdev.com>
+ * @date 2015
+ */
+#pragma once
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include "ethash.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Prepares io for ethash
+ * @param dirname        A null terminated c-string of the path of the ethash
+ *                       data directory. If it does not exist it's created.
+ * @param block_number   The current block number. Used in seedhash calculation.
+ * @returns              True if all went fine, and false if there was any kind
+ *                       of error
+ */
+bool ethash_io_prepare(char const *dirname, uint32_t block_number);
+void ethash_io_write();
+static inline void ethash_io_serialize_info(uint32_t revision,
+                                            uint32_t block_number,
+                                            char *output)
+{
+    // if .info is only consumed locally we don't really care about endianess
+    memcpy(output, &revision, 4);
+    ethash_get_seedhash((uint8_t*)(output + 4), block_number);
+}
+
+
+#ifdef __cplusplus
+}
+#endif

io_posix.c

@@ -0,0 +1,82 @@
+/*
+  This file is part of ethash.
+
+  ethash is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  ethash is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with ethash.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/** @file io_posix.c
+ * @author Lefteris Karapetsas <lefteris@ethdev.com>
+ * @date 2015
+ */
+#include "io.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <libgen.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+
+static const char DAG_FILE_NAME[] = "full";
+static const char DAG_MEMO_NAME[] = "full.info";
+static const unsigned int DAG_MEMO_BYTESIZE = 36;
+
+bool ethash_io_prepare(char const *dirname, uint32_t block_number)
+{
+    char read_buffer[DAG_MEMO_BYTESIZE];
+    char expect_buffer[DAG_MEMO_BYTESIZE];
+    bool ret = false;
+
+    // assert directory exists, full owner permissions and read/search for others
+    int rc = mkdir(dirname, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
+    if (rc == -1 && errno != EEXIST) {
+        goto end;
+    }
+
+    // try to open memo file
+    char *memofile = malloc(strlen(dirname) + sizeof(DAG_MEMO_NAME));
+    if (!memofile) {
+        goto end;
+    }
+
+    FILE *f = fopen(memofile, "rb");
+    if (!f) {
+        // file does not exist, so no checking happens. All is fine.
+        ret = true;
+        goto free_memo;
+    }
+
+    if (fread(read_buffer, 1, DAG_MEMO_BYTESIZE, f) != DAG_MEMO_BYTESIZE) {
+        goto free_memo;
+    }
+
+    ethash_io_serialize_info(REVISION, block_number, expect_buffer);
+    if (memcmp(read_buffer, expect_buffer, DAG_MEMO_BYTESIZE) != 0) {
+        // we have different memo contents so delete the memo file
+        if (unlink(memofile) != 0) {
+            goto free_memo;
+        }
+    }
+
+    ret = true;
+
+free_memo:
+    free(memofile);
+end:
+    return ret;
+}
+
+void ethash_io_write()
+{
+}
+