added diskstore.c, currently just a stub

src/diskstore.c

+/* diskstore.c implements a very simple disk backed key-value store used
+ * by Redis for the "disk" backend. This implementation uses the filesystem
+ * to store key/value pairs. Every file represents a given key.
+ *
+ * The key path is calculated using the SHA1 of the key name. For instance
+ * the key "foo" is stored as a file name called:
+ *
+ *  /0b/ee/0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33
+ *
+ * The couples of characters from the hex output of SHA1 are also used
+ * to locate two two levels of directories to store the file (as most
+ * filesystems are not able to handle too many files in a single dir).
+ *
+ * In the end there are 65536 final directories (256 directories inside
+ * every 256 top level directories), so that with 1 billion of files every
+ * directory will contain in the average 15258 entires, that is ok with
+ * most filesystems implementation.
+ *
+ * The actaul implementation of this disk store is highly related to the
+ * filesystem implementation. This implementation may be replaced by
+ * a B+TREE implementation in future implementations.
+ *
+ * Data ok every key is serialized using the same format used for .rdb
+ * serialization. Everything is serialized on every entry: key name,
+ * ttl information in case of keys with an associated expire time, and the
+ * serialized value itself.
+ *
+ * Because the format is the same of the .rdb files it is trivial to create
+ * an .rdb file starting from this format just by mean of scanning the
+ * directories and concatenating entries, with the sole addition of an
+ * .rdb header at the start and the end-of-db opcode at the end.
+ *
+ * -------------------------------------------------------------------------
+ *
+ * Copyright (c) 2010-2011, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "redis.h"
+
+#include <fcntl.h>
+#include <sys/stat.h>
+
+int dsOpen(void) {
+    struct stat sb;
+    int retval;
+    char *path = server.diskstore_path;
+
+    if ((retval = stat(path,&sb) == -1) && errno != ENOENT) {
+        redisLog(REDIS_WARNING, "Error opening disk store at %s: %s",
+                path, strerror(errno));
+        return REDIS_ERR;
+    }
+
+    /* Directory already in place. Assume everything is ok. */
+    if (retval == 0 && S_ISDIR(sb.st_mode)) return REDIS_OK;
+
+    /* File exists but it's not a directory */
+    if (retval == 0 && !S_ISDIR(sb.st_mode)) {
+        redisLog(REDIS_WARNING,"Disk store at %s is not a directory", path);
+        return REDIS_ERR;
+    }
+
+    /* New disk store, create the directory structure now, as creating
+     * them in a lazy way is not a good idea, after very few insertions
+     * we'll need most of the 65536 directories anyway. */
+    if (mkdir(path) == -1) {
+        redisLog(REDIS_WARNING,"Disk store init failed creating dir %s: %s",
+            path, strerror(errno));
+        return REDIS_ERR;
+    }
+    return REDIS_OK;
+}
+
+int dsClose(void) {
+    return REDIS_OK;
+}
+
+int dsSet(redisDb *db, robj *key, robj *val) {
+}
+
+robj *dsGet(redisDb *db, robj *key) {
+}
+
+int dsExists(redisDb *db, robj *key) {
+}