diff --git a/check.c b/check.c
index c7e841a8..a13280db 100644
--- a/check.c
+++ b/check.c
@@ -1185,7 +1185,7 @@ close_and_continue:
 			char path[PATH_MAX];
 			struct stat st;
 			struct snapraid_file* file;
-			int failed = 0;
+			int unsuccesful = 0;
 
 			file = node->data;
 			node = node->next; /* next node */
@@ -1204,24 +1204,24 @@ close_and_continue:
 			pathprint(path, sizeof(path), "%s%s", disk->dir, file->sub);
 			ret = stat(path, &st);
 			if (ret == -1) {
-				failed = 1;
+				unsuccesful = 1;
 
 				fprintf(stdlog, "Error stating empty file '%s'. %s.\n", path, strerror(errno));
 				fprintf(stdlog, "error:%s:%s: Empty file stat error\n", disk->name, file->sub);
 				++error;
 			} else if (!S_ISREG(st.st_mode)) {
-				failed = 1;
+				unsuccesful = 1;
 
 				fprintf(stdlog, "error:%s:%s: Empty file error for not regular file\n", disk->name, file->sub);
 				++error;
 			} else if (st.st_size != 0) {
-				failed = 1;
+				unsuccesful = 1;
 
 				fprintf(stdlog, "error:%s:%s: Empty file error for size '%"PRIu64"'\n", disk->name, file->sub, st.st_size);
 				++error;
 			}
 
-			if (fix && failed) {
+			if (fix && unsuccesful) {
 				int f;
 
 				/* create the ancestor directories */
@@ -1297,7 +1297,7 @@ close_and_continue:
 			struct stat st;
 			struct stat stto;
 			struct snapraid_link* link;
-			int failed = 0;
+			int unsuccesful = 0;
 			int unrecoverable = 0;
 
 			link = node->data;
@@ -1313,13 +1313,13 @@ close_and_continue:
 				pathprint(path, sizeof(path), "%s%s", disk->dir, link->sub);
 				ret = stat(path, &st);
 				if (ret == -1) {
-					failed = 1;
+					unsuccesful = 1;
 
 					fprintf(stdlog, "Error stating hardlink '%s'. %s.\n", path, strerror(errno));
 					fprintf(stdlog, "hardlinkerror:%s:%s:%s: Hardlink stat error\n", disk->name, link->sub, link->linkto);
 					++error;
 				} else if (!S_ISREG(st.st_mode)) {
-					failed = 1;
+					unsuccesful = 1;
 
 					fprintf(stdlog, "hardlinkerror:%s:%s:%s: Hardlink error for not regular file\n", disk->name, link->sub, link->linkto);
 					++error;
@@ -1329,7 +1329,7 @@ close_and_continue:
 				pathprint(pathto, sizeof(pathto), "%s%s", disk->dir, link->linkto);
 				ret = stat(pathto, &stto);
 				if (ret == -1) {
-					failed = 1;
+					unsuccesful = 1;
 
 					if (errno == ENOENT) {
 						unrecoverable = 1;
@@ -1349,12 +1349,12 @@ close_and_continue:
 					fprintf(stdlog, "hardlinkerror:%s:%s:%s: Hardlink to stat error\n", disk->name, link->sub, link->linkto);
 					++error;
 				} else if (!S_ISREG(stto.st_mode)) {
-					failed = 1;
+					unsuccesful = 1;
 
 					fprintf(stdlog, "hardlinkerror:%s:%s:%s: Hardlink-to error for not regular file\n", disk->name, link->sub, link->linkto);
 					++error;
-				} else if (!failed && st.st_ino != stto.st_ino) {
-					failed = 1;
+				} else if (!unsuccesful && st.st_ino != stto.st_ino) {
+					unsuccesful = 1;
 
 					fprintf(stdlog, "Mismatch hardlink '%s' and '%s'. Different inode.\n", path, pathto);
 					fprintf(stdlog, "hardlinkerror:%s:%s:%s: Hardlink mismatch for different inode\n", disk->name, link->sub, link->linkto);
@@ -1365,13 +1365,13 @@ close_and_continue:
 				pathprint(path, sizeof(path), "%s%s", disk->dir, link->sub);
 				ret = readlink(path, linkto, sizeof(linkto));
 				if (ret < 0) {
-					failed = 1;
+					unsuccesful = 1;
 
 					fprintf(stdlog, "Error reading symlink '%s'. %s.\n", path, strerror(errno));
 					fprintf(stdlog, "symlinkerror:%s:%s: Symlink read error\n", disk->name, link->sub);
 					++error;
 				} else if (ret >= PATH_MAX) {
-					failed = 1;
+					unsuccesful = 1;
 
 					fprintf(stdlog, "Error reading symlink '%s'. Symlink too long.\n", path);
 					fprintf(stdlog, "symlinkerror:%s:%s: Symlink read error\n", disk->name, link->sub);
@@ -1380,7 +1380,7 @@ close_and_continue:
 					linkto[ret] = 0;
 
 					if (strcmp(linkto, link->linkto) != 0) {
-						failed = 1;
+						unsuccesful = 1;
 
 						fprintf(stdlog, "symlinkerror:%s:%s: Symlink data error '%s' instead of '%s'\n", disk->name, link->sub, linkto, link->linkto);
 						++error;
@@ -1388,7 +1388,7 @@ close_and_continue:
 				}
 			}
 
-			if (fix && failed && !unrecoverable) {
+			if (fix && unsuccesful && !unrecoverable) {
 				/* create the ancestor directories */
 				ret = mkancestor(path);
 				if (ret != 0) {
@@ -1467,7 +1467,7 @@ close_and_continue:
 			char path[PATH_MAX];
 			struct stat st;
 			struct snapraid_dir* dir;
-			int failed = 0;
+			int unsuccesful = 0;
 
 			dir = node->data;
 			node = node->next; /* next node */
@@ -1481,19 +1481,19 @@ close_and_continue:
 			pathprint(path, sizeof(path), "%s%s", disk->dir, dir->sub);
 			ret = stat(path, &st);
 			if (ret == -1) {
-				failed = 1;
+				unsuccesful = 1;
 
 				fprintf(stdlog, "Error stating dir '%s'. %s.\n", path, strerror(errno));
 				fprintf(stdlog, "dir_error:%s:%s: Dir stat error\n", disk->name, dir->sub);
 				++error;
 			} else if (!S_ISDIR(st.st_mode)) {
-				failed = 1;
+				unsuccesful = 1;
 
 				fprintf(stdlog, "dir_error:%s:%s: Dir error for not directory\n", disk->name, dir->sub);
 				++error;
 			}
 
-			if (fix && failed) {
+			if (fix && unsuccesful) {
 				/* create the ancestor directories */
 				ret = mkancestor(path);
 				if (ret != 0) {
diff --git a/configure.ac b/configure.ac
index 5a54b7a7..254aa023 100644
--- a/configure.ac
+++ b/configure.ac
@@ -148,6 +148,19 @@ AC_ARG_ENABLE([debug],
 	],
 	[])
 
+AC_ARG_ENABLE([warning],
+	[AS_HELP_STRING([--enable-warning],[enable extra warning])],
+	[
+	AC_CHECK_CC_OPT([-Wpointer-arith], CFLAGS="$CFLAGS -Wpointer-arith", [])
+	AC_CHECK_CC_OPT([-Wcast-qual], CFLAGS="$CFLAGS -Wcast-qual", [])
+	AC_CHECK_CC_OPT([-Wunused], CFLAGS="$CFLAGS -Wunused", [])
+	AC_CHECK_CC_OPT([-Wunreachable-code], CFLAGS="$CFLAGS -Wunreachable-code", [])
+	AC_CHECK_CC_OPT([-Wpadded], CFLAGS="$CFLAGS -Wpadded", [])
+	AC_CHECK_CC_OPT([-Wshadow], CFLAGS="$CFLAGS -Wshadow", [])
+	AC_CHECK_CC_OPT([-Weverything], CFLAGS="$CFLAGS -Weverything", [])
+	],
+	[])
+
 AC_ARG_VAR([TESTENV], [Test environment])
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT
diff --git a/import.c b/import.c
index a3d4ffbe..56b3d198 100644
--- a/import.c
+++ b/import.c
@@ -45,7 +45,7 @@ int import_block_prevhash_compare(const void* void_arg, const void* void_data)
  */
 static inline tommy_uint32_t import_block_hash(const unsigned char* hash)
 {
-	return *(tommy_uint32_t*)hash;
+	return *(const tommy_uint32_t*)hash;
 }
 
 static void import_file(struct snapraid_state* state, const char* path, uint64_t size)
diff --git a/murmur3.c b/murmur3.c
index dddf62b3..54dc1961 100644
--- a/murmur3.c
+++ b/murmur3.c
@@ -82,10 +82,10 @@ void MurmurHash3_x86_128(const void* key, unsigned len, const uint8_t* seed, voi
 	unsigned i;
 	const uint32_t* blocks;
 
-	uint32_t h1 = ((uint32_t*)seed)[0];
-	uint32_t h2 = ((uint32_t*)seed)[1];
-	uint32_t h3 = ((uint32_t*)seed)[2];
-	uint32_t h4 = ((uint32_t*)seed)[3];
+	uint32_t h1 = ((const uint32_t*)seed)[0];
+	uint32_t h2 = ((const uint32_t*)seed)[1];
+	uint32_t h3 = ((const uint32_t*)seed)[2];
+	uint32_t h4 = ((const uint32_t*)seed)[3];
 
 #if WORDS_BIGENDIAN
 	h1 = util_swap32(h1);
diff --git a/scan.c b/scan.c
index ed67307f..a70913e4 100644
--- a/scan.c
+++ b/scan.c
@@ -874,7 +874,7 @@ struct dirent_sorted {
 #if HAVE_STRUCT_DIRENT_D_STAT
 	struct stat d_stat; /**< Stat result. */
 #endif
-	char d_name[1]; /**< Variable length name. It must be the last field. */
+	char d_name[]; /**< Variable length name. It must be the last field. */
 };
 
 #if HAVE_STRUCT_DIRENT_D_INO
@@ -995,7 +995,7 @@ static int scan_dir(struct snapraid_scan* scan, int output, const char* dir, con
 		}
 
 		name_len = strlen(dd->d_name);
-		entry = malloc_nofail(sizeof(struct dirent_sorted) + name_len);
+		entry = malloc_nofail(sizeof(struct dirent_sorted) + name_len + 1);
 
 		/* copy the dir entry */
 #if HAVE_STRUCT_DIRENT_D_INO
diff --git a/scrub.c b/scrub.c
index d80e52ea..7d94aeeb 100644
--- a/scrub.c
+++ b/scrub.c
@@ -134,7 +134,6 @@ static int state_scrub_process(struct snapraid_state* state, struct snapraid_par
 		int error_on_this_block;
 		int silent_error_on_this_block;
 		int block_is_unsynced;
-		int ret;
 		int rehash;
 
 		/* if it's unused */
diff --git a/spooky2.c b/spooky2.c
index c4a393e5..14a48dd4 100644
--- a/spooky2.c
+++ b/spooky2.c
@@ -123,8 +123,8 @@ void SpookyHash128(const void* message, size_t length, const uint8_t* seed, uint
 	unsigned i;
 #endif
 
-	h9 = ((uint64_t*)seed)[0];
-	h10 = ((uint64_t*)seed)[1];
+	h9 = ((const uint64_t*)seed)[0];
+	h10 = ((const uint64_t*)seed)[1];
 
 #if WORDS_BIGENDIAN
 	h9 = util_swap64(h9);
diff --git a/state.c b/state.c
index 8b8e3368..bbe7c94d 100644
--- a/state.c
+++ b/state.c
@@ -452,20 +452,20 @@ void state_config(struct snapraid_state* state, const char* path, const char* co
 		) {
 			char device[PATH_MAX];
 			char* slash;
-			unsigned l;
+			unsigned level;
 
 			switch (tag[0]) {
-			case 'p' : l = 0; break;
-			case 'q' : l = 1; break;
-			case 'r' : l = 2; break;
-			case '1' : l = 0; break;
-			case '2' : l = 1; break;
-			case '3' : l = 2; break;
-			case '4' : l = 3; break;
-			case '5' : l = 4; break;
-			case '6' : l = 5; break;
+			case 'p' : level = 0; break;
+			case 'q' : level = 1; break;
+			case 'r' : level = 2; break;
+			case '1' : level = 0; break;
+			case '2' : level = 1; break;
+			case '3' : level = 2; break;
+			case '4' : level = 3; break;
+			case '5' : level = 4; break;
+			case '6' : level = 5; break;
 			case 'z' :
-				l = 2;
+				level = 2;
 				state->raid_mode = RAID_MODE_VANDERMONDE;
 				break;
 			default:
@@ -475,7 +475,7 @@ void state_config(struct snapraid_state* state, const char* path, const char* co
 				/* LCOV_EXCL_STOP */
 			}
 
-			if (*state->parity_path[l]) {
+			if (*state->parity_path[level]) {
 				/* LCOV_EXCL_START */
 				fprintf(stderr, "Multiple '%s' specification in '%s' at line %u\n", tag, path, line);
 				exit(EXIT_FAILURE);
@@ -497,7 +497,7 @@ void state_config(struct snapraid_state* state, const char* path, const char* co
 				/* LCOV_EXCL_STOP */
 			}
 
-			pathimport(state->parity_path[l], sizeof(state->parity_path[l]), buffer);
+			pathimport(state->parity_path[level], sizeof(state->parity_path[level]), buffer);
 
 			if (state->opt.skip_parity_access) {
 				struct stat st;
@@ -516,15 +516,15 @@ void state_config(struct snapraid_state* state, const char* path, const char* co
 					/* LCOV_EXCL_STOP */
 				}
 
-				state->parity_device[l] = st.st_dev;
+				state->parity_device[level] = st.st_dev;
 			} else {
 				/* if parity is skipped, uses a fake device */
-				state->parity_device[l] = -1LL - l;
+				state->parity_device[level] = -1LL - level;
 			}
 
 			/* adjust the level */
-			if (state->level < l + 1)
-				state->level = l + 1;
+			if (state->level < level + 1)
+				state->level = level + 1;
 		} else if (strcmp(tag, "share") == 0) {
 			if (*state->share) {
 				/* LCOV_EXCL_START */
@@ -2615,7 +2615,6 @@ static void state_read_binary(struct snapraid_state* state, const char* path, ST
 	}
 
 	while (1) {
-		char buffer[PATH_MAX];
 		int c;
 
 		/* read the command */
diff --git a/sync.c b/sync.c
index 4f5b9bc7..db087779 100644
--- a/sync.c
+++ b/sync.c
@@ -412,7 +412,6 @@ static int state_sync_process(struct snapraid_state* state, struct snapraid_pari
 		int silent_error_on_this_block;
 		int fixed_error_on_this_block;
 		int parity_needs_to_be_updated;
-		int ret;
 		snapraid_info info;
 		int rehash;
 
diff --git a/tommyhash.c b/tommyhash.c
index 77431417..0bc604d9 100644
--- a/tommyhash.c
+++ b/tommyhash.c
@@ -35,7 +35,7 @@ tommy_inline tommy_uint32_t tommy_le_uint32_read(const void* ptr)
 	/* allow unaligned read on Intel x86 and x86_64 platforms */
 #if defined(__i386__) || defined(_M_IX86) || defined(_X86_) || defined(__x86_64__) || defined(_M_X64)
 	/* defines from http://predef.sourceforge.net/ */
-	return *(tommy_uint32_t*)ptr;
+	return *(const tommy_uint32_t*)ptr;
 #else
 	const unsigned char* ptr8 = tommy_cast(const unsigned char*, ptr);
 	return ptr8[0] + ((tommy_uint32_t)ptr8[1] << 8) + ((tommy_uint32_t)ptr8[2] << 16) + ((tommy_uint32_t)ptr8[3] << 24);
diff --git a/util.c b/util.c
index e48ff2d7..720d6182 100644
--- a/util.c
+++ b/util.c
@@ -1198,14 +1198,14 @@ uint32_t crc32c_x86(uint32_t crc, const unsigned char* ptr, unsigned size)
 #ifdef CONFIG_X86_64
 	crc64 = crc;
 	while (size >= 8) {
-		asm volatile ("crc32q %1, %0\n" : "+r" (crc64) : "rm" (*(uint64_t*)ptr));
+		asm volatile ("crc32q %1, %0\n" : "+r" (crc64) : "rm" (*(const uint64_t*)ptr));
 		ptr += 8;
 		size -= 8;
 	}
 	crc = crc64;
 #else
 	while (size >= 4) {
-		asm volatile ("crc32l %1, %0\n" : "+r" (crc) : "rm" (*(uint32_t*)ptr));
+		asm volatile ("crc32l %1, %0\n" : "+r" (crc) : "rm" (*(const uint32_t*)ptr));
 		ptr += 4;
 		size -= 4;
 	}