Index: uspace/srv/fs/exfat/exfat_bitmap.c
===================================================================
--- uspace/srv/fs/exfat/exfat_bitmap.c	(revision bf848717e8d508127f8be22655d603fdd89fe773)
+++ uspace/srv/fs/exfat/exfat_bitmap.c	(revision 63bcbbccef2e1a74b2296d6a3d6df3f70784cdaa)
@@ -45,5 +45,4 @@
 #include <assert.h>
 #include <fibril_synch.h>
-#include <malloc.h>
 #include <mem.h>
 
Index: uspace/srv/fs/exfat/exfat_dentry.c
===================================================================
--- uspace/srv/fs/exfat/exfat_dentry.c	(revision bf848717e8d508127f8be22655d603fdd89fe773)
+++ uspace/srv/fs/exfat/exfat_dentry.c	(revision 63bcbbccef2e1a74b2296d6a3d6df3f70784cdaa)
@@ -101,11 +101,30 @@
 bool exfat_valid_char(wchar_t ch)
 {
-	/* TODO */
-	return true;
+	switch (ch) {
+	case 0x01 ... 0x1F:
+	case '/':
+	case '\\':
+	case '?':
+	case '|':
+	case '>':
+	case '<':
+	case '"':
+	case '*':
+	case ':':
+		return false;
+	default:
+		return true;
+	}
 }
 
 bool exfat_valid_name(const char *name)
 {
-	/* TODO */
+	size_t off = 0;
+	wchar_t ch;
+
+	while ((ch = str_decode(name, &off, STR_NO_LIMIT)) != 0) {
+		if (!exfat_valid_char(ch))
+			return false;
+	}
 	return true;
 }
Index: uspace/srv/fs/exfat/exfat_directory.c
===================================================================
--- uspace/srv/fs/exfat/exfat_directory.c	(revision bf848717e8d508127f8be22655d603fdd89fe773)
+++ uspace/srv/fs/exfat/exfat_directory.c	(revision 63bcbbccef2e1a74b2296d6a3d6df3f70784cdaa)
@@ -112,4 +112,6 @@
 		rc = block_put(di->b);
 		di->b = NULL;
+		if (rc != EOK)
+			return rc;
 	}
 	if (!di->b) {
@@ -266,5 +268,6 @@
 		if (idx == 2 || idx == 3)
 			continue;
-		checksum = ((checksum << 15) | (checksum >> 1)) + (uint16_t)bytes[idx];
+		checksum = ((checksum << 15) | (checksum >> 1)) +
+		    (uint16_t)bytes[idx];
 	}
 	return checksum;
@@ -310,5 +313,6 @@
 	array[1].stream.valid_data_size = host2uint64_t_le(ds->valid_data_size);
 	array[1].stream.data_size = host2uint64_t_le(ds->data_size);
-	array[0].file.checksum = host2uint16_t_le(exfat_directory_set_checksum((uint8_t *)array,
+	array[0].file.checksum =
+	    host2uint16_t_le(exfat_directory_set_checksum((uint8_t *)array,
 	    count * sizeof(exfat_dentry_t)));
 
@@ -352,5 +356,6 @@
 	uctablep = EXFAT_NODE(fn);
 
-	uctable_chars = ALIGN_DOWN(uctablep->size, sizeof(uint16_t)) / sizeof(uint16_t); 
+	uctable_chars = ALIGN_DOWN(uctablep->size,
+	    sizeof(uint16_t)) / sizeof(uint16_t); 
 	uctable = (uint16_t *) malloc(uctable_chars * sizeof(uint16_t));
 	rc = exfat_read_uctable(di->bs, uctablep, (uint8_t *)uctable);
@@ -417,6 +422,9 @@
 			return rc;
 
-		if (i == df.file.count - 2)
-			chars = ds.stream.name_size - EXFAT_NAME_PART_LEN*(df.file.count - 2);
+		if (i == df.file.count - 2) {
+			chars = ds.stream.name_size -
+			    EXFAT_NAME_PART_LEN*(df.file.count - 2);
+		}
+
 		rc = exfat_directory_get(di, &de);
 		if (rc != EOK)
Index: uspace/srv/fs/exfat/exfat_fat.c
===================================================================
--- uspace/srv/fs/exfat/exfat_fat.c	(revision bf848717e8d508127f8be22655d603fdd89fe773)
+++ uspace/srv/fs/exfat/exfat_fat.c	(revision 63bcbbccef2e1a74b2296d6a3d6df3f70784cdaa)
@@ -50,4 +50,5 @@
 #include <malloc.h>
 #include <mem.h>
+#include <str.h>
 
 
@@ -322,9 +323,9 @@
 			    (found == 0) ?  EXFAT_CLST_EOF : lifo[found - 1]);
 			if (rc != EOK)
-				break;
+				goto exit_error;
 			found++;
 			rc = bitmap_set_cluster(bs, service_id, clst);
 			if (rc != EOK)
-				break;
+				goto exit_error;
 
 		}
@@ -339,4 +340,8 @@
 	}
 
+	rc = ENOSPC;
+
+exit_error:
+
 	/* If something wrong - free the clusters */
 	while (found--) {
@@ -347,5 +352,5 @@
 	free(lifo);
 	fibril_mutex_unlock(&exfat_alloc_lock);
-	return ENOSPC;
+	return rc;
 }
 
@@ -537,5 +542,18 @@
 int exfat_sanity_check(exfat_bs_t *bs, service_id_t service_id)
 {
-	/* TODO */
+	if (str_cmp((char const *)bs->oem_name, "EXFAT   "))
+		return ENOTSUP;
+	else if (uint16_t_le2host(bs->signature) != 0xAA55)
+		return ENOTSUP;
+	else if (uint32_t_le2host(bs->fat_sector_count) == 0)
+		return ENOTSUP;
+	else if (uint32_t_le2host(bs->data_clusters) == 0)
+		return ENOTSUP;
+	else if (bs->fat_count != 1)
+		return ENOTSUP;
+	else if ((bs->bytes_per_sector + bs->sec_per_cluster) > 25) {
+		/* exFAT does not support cluster size > 32 Mb */
+		return ENOTSUP;
+	}
 	return EOK;
 }
Index: uspace/srv/fs/exfat/exfat_ops.c
===================================================================
--- uspace/srv/fs/exfat/exfat_ops.c	(revision bf848717e8d508127f8be22655d603fdd89fe773)
+++ uspace/srv/fs/exfat/exfat_ops.c	(revision 63bcbbccef2e1a74b2296d6a3d6df3f70784cdaa)
@@ -657,4 +657,11 @@
 			return rc;
 		}
+
+		rc = exfat_zero_cluster(bs, service_id, nodep->firstc);
+		if (rc != EOK) {
+			(void) exfat_node_put(FS_NODE(nodep));
+			return rc;
+		}
+
 		nodep->size = BPC(bs);
 	} else {
@@ -739,9 +746,14 @@
 	 */
 	rc = exfat_directory_write_file(&di, name);
-	if (rc != EOK)
-		return rc;
+	if (rc != EOK) {
+		(void) exfat_directory_close(&di);
+		fibril_mutex_unlock(&parentp->idx->lock);
+		return rc;
+	}
 	rc = exfat_directory_close(&di);
-	if (rc != EOK)
-		return rc;
+	if (rc != EOK) {
+		fibril_mutex_unlock(&parentp->idx->lock);
+		return rc;
+	}
 
 	fibril_mutex_unlock(&parentp->idx->lock);
@@ -1258,5 +1270,7 @@
 		exfat_directory_t di;
 		rc = exfat_directory_open(nodep, &di);
-		if (rc != EOK) goto err;
+		if (rc != EOK)
+			goto err;
+
 		rc = exfat_directory_seek(&di, pos);
 		if (rc != EOK) {
@@ -1268,7 +1282,9 @@
 		    &df, &ds);
 		if (rc == EOK)
-		    goto hit;
-		if (rc == ENOENT)
-		    goto miss;
+			goto hit;
+		else if (rc == ENOENT)
+			goto miss;
+
+		(void) exfat_directory_close(&di);
 
 err:
@@ -1279,5 +1295,5 @@
 miss:
 		rc = exfat_directory_close(&di);
-		if (rc!=EOK)
+		if (rc != EOK)
 			goto err;
 		rc = exfat_node_put(fn);
@@ -1397,5 +1413,5 @@
 
 	(void) async_data_write_finalize(callid,
-		b->data + pos % BPS(bs), bytes);
+	    b->data + pos % BPS(bs), bytes);
 	b->dirty = true;		/* need to sync block */
 	rc = block_put(b);