diff --git a/SConstruct b/SConstruct
index 361f96e..074c164 100644
--- a/SConstruct
+++ b/SConstruct
@@ -185,6 +185,7 @@ SConscript('bin/ethinject/SConscript', variant_dir='build/bin/ethinject')
 SConscript('bin/false/SConscript', variant_dir='build/bin/false')
 SConscript('bin/ls/SConscript', variant_dir='build/bin/ls')
 SConscript('bin/shell/SConscript', variant_dir='build/bin/shell')
+SConscript('bin/stat/SConscript', variant_dir='build/bin/stat')
 SConscript('bin/true/SConscript', variant_dir='build/bin/true')
 SConscript('sbin/ifconfig/SConscript', variant_dir='build/sbin/ifconfig')
 SConscript('sbin/init/SConscript', variant_dir='build/sbin/init')
@@ -217,12 +218,14 @@ if env["BOOTDISK"] == "1":
     Depends(bootdisk, "#build/bin/false/false")
     Depends(bootdisk, "#build/bin/ls/ls")
     Depends(bootdisk, "#build/bin/shell/shell")
+    Depends(bootdisk, "#build/bin/stat/stat")
     Depends(bootdisk, "#build/bin/true/true")
     Depends(bootdisk, "#build/sbin/ifconfig/ifconfig")
     Depends(bootdisk, "#build/sbin/init/init")
     Depends(bootdisk, "#build/sbin/sysctl/sysctl")
     Depends(bootdisk, "#build/sys/castor")
     #Depends(bootdisk, "#build/tests/lwiptest")
+    Depends(bootdisk, "#build/tests/fiotest")
     Depends(bootdisk, "#build/tests/pthreadtest")
     Depends(bootdisk, "#build/tests/spawnanytest")
     Depends(bootdisk, "#build/tests/spawnmultipletest")
diff --git a/bin/stat/SConscript b/bin/stat/SConscript
new file mode 100644
index 0000000..3c38171
--- /dev/null
+++ b/bin/stat/SConscript
@@ -0,0 +1,23 @@
+import sys
+
+Import('env')
+
+init_env = env.Clone()
+
+src = [ ]
+
+src_common = [
+    "stat.c"
+]
+
+src.append(env["CRTBEGIN"])
+src.append(src_common)
+src.append(env["CRTEND"])
+
+init_env.Append(LINKFLAGS = ['-nostdlib'])
+init_env.Append(CPPFLAGS = ['-fno-builtin', '-nostdinc'])
+init_env.Append(CPPPATH = ['#build/include'])
+init_env.Append(LIBPATH = ['#build/lib/libc'], LIBS = ['c'])
+
+init_env.Program("stat", src)
+
diff --git a/bin/stat/stat.c b/bin/stat/stat.c
new file mode 100644
index 0000000..4c4a0f8
--- /dev/null
+++ b/bin/stat/stat.c
@@ -0,0 +1,42 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <sys/stat.h>
+
+// Castor Only
+#include <syscall.h>
+
+int
+main(int argc, const char *argv[])
+{
+    int i;
+    int status, fd;
+    struct stat sb;
+    char buf[256];
+
+    if (argc < 2) {
+	fputs("Requires an argument\n", stdout);
+	return 1;
+    }
+
+    if (argc > 2) {
+	fputs("Too many arguments, expected one\n", stdout);
+	return 1;
+    }
+
+    status = OSStat(argv[1], &sb);
+    if (status != 0) {
+	fputs("Cannot stat file\n", stdout);
+	return 0;
+    }
+
+    printf("  File: \"%s\"\n", argv[1]);
+    printf("  Size: %d\n", sb.st_size);
+    printf("Blocks: %d\n", sb.st_blocks);
+    printf(" Inode: %d\n", sb.st_ino);
+
+    return 0;
+}
+
diff --git a/include/errno.h b/include/errno.h
index cc8f0ce..37be525 100644
--- a/include/errno.h
+++ b/include/errno.h
@@ -25,6 +25,7 @@ int *__error();
 #define ETIMEDOUT	0x1BAD0010
 #define EACCES		0x1BAD0011
 #define EPERM		0x1BAD0012
+#define ENOSPC		0x1BAD0013
 
 #define EAFNOSUPPORT	0x1BAD0020
 #define ENOPROTOOPT	0x1BAD0021
diff --git a/release/bootdisk.manifest b/release/bootdisk.manifest
index fa384da..cce7202 100644
--- a/release/bootdisk.manifest
+++ b/release/bootdisk.manifest
@@ -11,6 +11,7 @@ DIR /
     FILE false build/bin/false/false
     FILE ls build/bin/ls/ls
     FILE shell build/bin/shell/shell
+    FILE stat build/bin/stat/stat
     FILE true build/bin/true/true
   END
   DIR sbin
@@ -21,6 +22,7 @@ DIR /
     FILE sysctl build/sbin/sysctl/sysctl
   END
   DIR tests
+    FILE fiotest build/tests/fiotest
     FILE pthreadtest build/tests/pthreadtest
     FILE spawnsingletest build/tests/spawnsingletest
     FILE spawnmultipletest build/tests/spawnmultipletest
diff --git a/sbin/newfs_o2fs/newfs_o2fs.c b/sbin/newfs_o2fs/newfs_o2fs.c
index f12b08c..08797ea 100644
--- a/sbin/newfs_o2fs/newfs_o2fs.c
+++ b/sbin/newfs_o2fs/newfs_o2fs.c
@@ -15,6 +15,8 @@
 
 #include <o2fs.h>
 
+#define ROUND_UP(_a, _b) (((_a) + (_b) - 1)/(_b))
+
 #define MAXBLOCKSIZE (64*1024*1024)
 
 char tempbuf[MAXBLOCKSIZE];
@@ -25,6 +27,7 @@ bool hasManifest = false;
 uint64_t diskSize = 0;
 uint64_t diskOffset = 0;
 uint64_t blockSize = 16*1024;
+uint64_t bitmapSize;
 int diskfd;
 struct stat diskstat;
 
@@ -230,6 +233,30 @@ ObjID *AddDirectory()
     return id;
 }
 
+void BlockBitmap()
+{
+    off_t off = lseek(diskfd, 0, SEEK_CUR) / blockSize;
+
+    /* Code below only supports using the first 16K blocks */
+    assert(off < blockSize);
+
+    memset(tempbuf, 0, MAXBLOCKSIZE);
+
+    /* Mark the blocks in use up to the current offset */
+    assert(off > 8);
+    for (off_t i = 0; i < (off / 8); i++) {
+	tempbuf[i] = 0xFF;
+    }
+    for (off_t i = 0; i < (off % 8); i++) {
+	tempbuf[off / 8] |= 1 << i;
+    }
+
+    lseek(diskfd, blockSize, SEEK_SET);
+
+    for (int i = 0; i < bitmapSize; i++)
+	AppendBlock(tempbuf + (blockSize * i), blockSize);
+}
+
 void Superblock(ObjID *objid)
 {
     SuperBlock sb;
@@ -242,6 +269,8 @@ void Superblock(ObjID *objid)
     sb.versionMinor = O2FS_VERSION_MINOR;
     sb.blockCount = diskSize / blockSize;
     sb.blockSize = blockSize;
+    sb.bitmapSize = bitmapSize;
+    sb.bitmapOffset = blockSize;
 
     if (objid)
 	memcpy(&sb.root, objid, sizeof(ObjID));
@@ -332,10 +361,16 @@ int main(int argc, char * const *argv)
 	lseek(diskfd, 0, SEEK_SET);
     }
 
+    /* Skip superblock */
     diskOffset = blockSize;
     lseek(diskfd, diskOffset, SEEK_SET);
     memset(zerobuf, 0, MAXBLOCKSIZE);
 
+    /* Zero the bitmap (and skip past it) */
+    bitmapSize = ROUND_UP(diskSize / (blockSize * 8), blockSize);
+    for (int i = 0; i < bitmapSize; i++)
+	AppendBlock(zerobuf, blockSize);
+
     ObjID *root = NULL;
     if (hasManifest) {
 	int tok;
@@ -359,6 +394,9 @@ int main(int argc, char * const *argv)
 	}
     }
 
+    /* Write bitmap */
+    BlockBitmap();
+
     Superblock(root);
     free(root);
 
diff --git a/sys/dev/x86/ide.c b/sys/dev/x86/ide.c
index e0c56a5..8275b20 100644
--- a/sys/dev/x86/ide.c
+++ b/sys/dev/x86/ide.c
@@ -34,10 +34,10 @@
 #define IDE_COMMAND		7   /* Write */
 #define IDE_STATUS		7   /* Read */
 
-// IDE Commands
+// IDE Commands (PIO)
 #define IDE_CMD_READ		0x20
 #define IDE_CMD_READ_EXT	0x24
-#define IDE_CMD_WRITE
+#define IDE_CMD_WRITE		0x30
 #define IDE_CMD_WRITE_EXT	0x34
 #define IDE_CMD_FLUSH		0xE7
 #define IDE_CMD_IDENTIFY	0xEC
@@ -77,6 +77,7 @@ int IDE_Read(Disk *disk, void *buf, SGArray *sga, DiskCB, void *arg);
 int IDE_Write(Disk *disk, void *buf, SGArray *sga, DiskCB, void *arg);
 int IDE_Flush(Disk *disk, void *buf, SGArray *sga, DiskCB, void *arg);
 int IDE_ReadOne(IDEDrive *drive, void *buf, uint64_t off, uint64_t len);
+int IDE_WriteOne(IDEDrive *drive, void *buf, uint64_t off, uint64_t len);
 
 IDE primary;
 IDEDrive primaryDrives[2];
@@ -291,7 +292,23 @@ IDE_Read(Disk *disk, void *buf, SGArray *sga, DiskCB cb, void *arg)
 int
 IDE_Write(Disk *disk, void *buf, SGArray *sga, DiskCB cb, void *arg)
 {
-    return -1;
+    int i;
+    int status;
+    IDEDrive *idedrive;
+
+    idedrive = disk->handle;
+
+    for (i = 0; i < sga->len; i++) {
+	status = IDE_WriteOne(idedrive,
+			      buf,
+			      sga->entries[i].offset / 512,
+			      sga->entries[i].length / 512);
+	buf += sga->entries[i].length;
+	if (status < 0)
+	    return status;
+    }
+
+    return 0;
 }
 
 int
@@ -401,7 +418,7 @@ IDE_WriteOne(IDEDrive *drive, void *buf, uint64_t off, uint64_t len)
     uint8_t status;
     IDE *ide = drive->ide;
 
-    Log(ide, "Write %llx %llx\n", off, len);
+    DLOG(ide, "read %llx %llx\n", off, len);
 
     ASSERT(drive->drive == 0 || drive->drive == 1);
 
@@ -425,33 +442,46 @@ IDE_WriteOne(IDEDrive *drive, void *buf, uint64_t off, uint64_t len)
 	}
 	ide->lastDriveCode = driveCode;
     }
-    outb(ide->base + IDE_SECTORCOUNT, len >> 8);
-    outb(ide->base + IDE_LBALOW, off >> 24);
-    outb(ide->base + IDE_LBAMID, off >> 32);
-    outb(ide->base + IDE_LBAHIGH, off >> 40);
-    outb(ide->base + IDE_SECTORCOUNT, len);
-    outb(ide->base + IDE_LBALOW, off);
-    outb(ide->base + IDE_LBAMID, off >> 8);
-    outb(ide->base + IDE_LBAHIGH, off >> 16);
-    outb(ide->base + IDE_COMMAND, IDE_CMD_WRITE_EXT);
 
-    // XXX: Need timeout
-    while (1) {
-	status = inb(ide->base + IDE_STATUS);
-	if ((status & IDE_STATUS_BSY) == 0)
-	    break;
+    if (lba48) {
+	outb(ide->base + IDE_SECTORCOUNT, len >> 8);
+	outb(ide->base + IDE_LBALOW, off >> 24);
+	outb(ide->base + IDE_LBAMID, off >> 32);
+	outb(ide->base + IDE_LBAHIGH, off >> 40);
     }
+    outb(ide->base + IDE_SECTORCOUNT, len);
+    outb(ide->base + IDE_LBALOW, off & 0xff);
+    outb(ide->base + IDE_LBAMID, (off >> 8) & 0xff);
+    outb(ide->base + IDE_LBAHIGH, (off >> 16) & 0xff);
 
+    if (lba48)
+	outb(ide->base + IDE_COMMAND, IDE_CMD_WRITE_EXT);
+    else
+	outb(ide->base + IDE_COMMAND, IDE_CMD_WRITE);
+
+    status = IDEWaitForBusy(ide, false);
     if ((status & IDE_STATUS_ERR) != 0) {
 	Spinlock_Unlock(&ide->lock);
-	Log(ide, "Error trying write from drive %d\n", drive);
+	Log(ide, "Error trying read from drive %d\n", drive->drive);
 	return -1;
     }
+
+    int sectors;
+    for (sectors = 0; sectors < len; sectors++)
+    {
+	uint8_t *b = buf + sectors * IDE_SECTOR_SIZE;
+	outsw(ide->base + IDE_DATAPORT, b, 256);
+
+	status = IDEWaitForBusy(ide, true);
+	if ((status & IDE_STATUS_ERR) != 0) {
+	    Spinlock_Unlock(&ide->lock);
+	    Log(ide, "Error reading from drive %d\n", drive->drive);
+	    return -1;
+	}
+    }
     Spinlock_Unlock(&ide->lock);
 
-    // XXX: Loop on outw(ide->base, b + sectorOffset);
-
-    // XXX: CACHE FLUSH
+    // XXX: Flush cache ...
 
     return 0;
 }
diff --git a/sys/fs/o2fs/o2fs.c b/sys/fs/o2fs/o2fs.c
index 209af02..1740f0b 100644
--- a/sys/fs/o2fs/o2fs.c
+++ b/sys/fs/o2fs/o2fs.c
@@ -71,11 +71,30 @@ O2FS_Mount(Disk *disk)
 	return NULL;
     }
 
+    // Read bitmap
+    for (int i = 0; i < sb->bitmapSize; i++) {
+	ASSERT(i < 16);
+
+	BufCacheEntry *bentry;
+	uint64_t offset = sb->bitmapOffset + i * sb->blockSize;
+
+	if (BufCache_Read(disk, offset, &bentry) < 0) {
+	    Alert(o2fs, "Bitmap read failed\n");
+	    for (i = 0; i < 16; i++)
+		BufCache_Release(fs->bitmap[i]);
+	    BufCache_Release(entry);
+	    return NULL;
+	}
+
+	fs->bitmap[i] = bentry;
+    }
+
     DLOG(o2fs, "File system mounted\n");
     DLOG(o2fs, "Root @ 0x%llx\n", sb->root.offset);
 
     fs->fsptr = entry;
     fs->fsval = sb->root.offset;
+    fs->blksize = sb->blockSize;
 
     // Setup VFS structure
     fs->op = &O2FSOperations;
@@ -101,6 +120,91 @@ O2FS_Unmount(VFS *fs)
     return -1;
 }
 
+/**
+ * O2FSBAlloc --
+ *
+ * Allocate a block.
+ *
+ * @param [in] vfs VFS Instance.
+ *
+ * @return Block number.
+ */
+uint64_t
+O2FSBAlloc(VFS *fs)
+{
+    for (int i = 0; i < 16; i++) {
+	char *bitmap;
+	BufCacheEntry *bentry = fs->bitmap[i];
+
+	if (fs->bitmap[i] == NULL)
+	    break;
+
+	bitmap = bentry->buffer;
+	// XXX: Check for end of disk
+	for (int b = 0; b < fs->blksize; b++) {
+	    for (int bi = 0; bi < 8; bi++) {
+		if (((bitmap[b] >> bi) & 0x1) == 0) {
+		    /* Set bit */
+		    bitmap[b] |= (1 << bi);
+
+		    /* Write bitmap */
+		    BufCache_Write(bentry);
+
+		    /*
+		     * Block index is the sum of:
+		     *   blksize*8 blocks per bitmap entry
+		     *   8 blocks per bitmap byte
+		     *   bit #
+		     */
+		    uint64_t blk = fs->blksize*8*i + 8*b + bi;
+		    DLOG(o2fs, "BAlloc %lu\n", blk);
+		    return blk;
+		}
+	    }
+	}
+    }
+
+    Alert(o2fs, "Out of space!\n");
+    return 0;
+}
+
+/**
+ * O2FSBFree --
+ *
+ * Free a block.
+ *
+ * @param [in] vfs VFS Instance.
+ * @param [in] block Block number.
+ */
+void
+O2FSBFree(VFS *fs, uint64_t block)
+{
+    uint64_t bitoff = block & 0x7;
+    uint64_t bytoff = (block >> 8) % fs->blksize;
+    uint64_t bufoff = block / (fs->blksize*8);
+
+    DLOG(o2fs, "BFree %lu\n", block);
+
+    BufCacheEntry *bentry = fs->bitmap[bufoff];
+    ASSERT(bentry != NULL);
+
+    char *bitmap = bentry->buffer;
+
+    /* Mask out the bit */
+    bitmap[bytoff] &= ~(1 << bitoff);
+
+    /* Write the bitmap */
+    BufCache_Write(bentry);
+}
+
+/**
+ * O2FSLoadVNode --
+ *
+ * Load a VNode from the disk given an ObjID.
+ *
+ * @param [in] vfs VFS Instance.
+ * @param [in] oobjid Object ID.
+ */
 VNode *
 O2FSLoadVNode(VFS *fs, ObjID *objid)
 {
@@ -143,12 +247,66 @@ O2FSLoadVNode(VFS *fs, ObjID *objid)
     return vn;
 }
 
+/**
+ * O2FSGrowVNode --
+ *
+ * Grow a VNode.
+ *
+ * @param [in] vfs VFS Instance.
+ * @param [in] bn BNode for the object.
+ * @param [in] filesz New file size.
+ *
+ * @return 0 on success, otherwise error code.
+ */
+int
+O2FSGrowVNode(VNode *vn, uint64_t filesz)
+{
+    VFS *vfs = vn->vfs;
+    BufCacheEntry *vnEntry = (BufCacheEntry *)vn->fsptr;
+    BNode *bn = vnEntry->buffer;
+
+    if (filesz > (vfs->blksize * 64))
+	return -EINVAL;
+
+    for (int i = 0; i < ((filesz + vfs->blksize - 1) / vfs->blksize); i++) {
+	if (bn->direct[i].offset == 0) {
+	    uint64_t blkno = O2FSBAlloc(vfs);
+	    if (blkno == 0) {
+		return -ENOSPC;
+	    }
+
+	    bn->direct[i].offset = blkno * vfs->blksize;
+	}
+    }
+
+    DLOG(o2fs, "Growing: %d\n", filesz);
+    bn->size = filesz;
+
+    BufCache_Write(vnEntry);
+
+    return 0;
+}
+
+/**
+ * O2FSRetainVNode --
+ *
+ * Increment VNode reference count.
+ *
+ * @param [in] vn VNode.
+ */
 void
 O2FSRetainVNode(VNode *vn)
 {
     vn->refCount++;
 }
 
+/**
+ * O2FSReleaseVNode --
+ *
+ * Decrement VNode reference count and release it if reaches zero.
+ *
+ * @param [in] vn VNode.
+ */
 void
 O2FSReleaseVNode(VNode *vn)
 {
@@ -160,6 +318,16 @@ O2FSReleaseVNode(VNode *vn)
     }
 }
 
+/**
+ * O2FS_GetRoot --
+ *
+ * Read the root directory Inode.
+ *
+ * @param [in] fs VFS Instance.
+ * @param [out] dn VNode of the root directory.
+ *
+ * @return 0 on success, otherwise error.
+ */
 int
 O2FS_GetRoot(VFS *fs, VNode **dn)
 {
@@ -212,6 +380,17 @@ O2FSDumpDirEntry(BDirEntry *entry)
     VLOG(o2fs, "%16s %08llx %08llx\n", entry->name, entry->objId.offset, entry->size);
 }
 
+/**
+ * O2FS_Lookup --
+ *
+ * Lookup a directory entry within a given directory.
+ *
+ * @param [in] vn VNode of the directory to look through.
+ * @param [out] fn VNode of the entry if found.
+ * @param [in] name Name of the file.
+ *
+ * @return 0 on success, otherwise error.
+ */
 int
 O2FS_Lookup(VNode *dn, VNode **fn, const char *name)
 {
@@ -266,6 +445,16 @@ O2FS_Close(VNode *fn)
     return 0;
 }
 
+/**
+ * O2FS_Stat --
+ *
+ * Stat a VNode.
+ *
+ * @param [in] fn VNode of the file to stat.
+ * @param [out] statinfo Stat structure.
+ *
+ * @return 0 on success.
+ */
 int
 O2FS_Stat(VNode *fn, struct stat *statinfo)
 {
@@ -275,14 +464,28 @@ O2FS_Stat(VNode *fn, struct stat *statinfo)
     BufCacheEntry *fileEntry = (BufCacheEntry *)fn->fsptr;
     BNode *fileBN = fileEntry->buffer;
 
+    DLOG(o2fs, "O2FS %p %d\n", fileBN, fileBN->size);
+
+    statinfo->st_ino = fileEntry->diskOffset;
     statinfo->st_size = fileBN->size;
-    // XXX: support other fields
     statinfo->st_blocks = (fileBN->size + sb->blockSize - 1) / sb->blockSize;
     statinfo->st_blksize = sb->blockSize;
 
     return 0;
 }
 
+/**
+ * O2FS_Read --
+ *
+ * Read from a VNode.
+ *
+ * @param [in] fn VNode of the file.
+ * @param [out] buf Buffer to read into.
+ * @param [in] off Offset within the file.
+ * @param [in] len Length of the buffer to read.
+ *
+ * @return number of bytes on success, otherwise negative error code.
+ */
 int
 O2FS_Read(VNode *fn, void *buf, uint64_t off, uint64_t len)
 {
@@ -337,13 +540,85 @@ O2FS_Read(VNode *fn, void *buf, uint64_t off, uint64_t len)
     return readBytes;
 }
 
+/**
+ * O2FS_Write --
+ *
+ * Write to a VNode.
+ *
+ * @param [in] fn VNode of the file.
+ * @param [in] buf Buffer to write out.
+ * @param [in] off Offset within the file.
+ * @param [in] len Length of the buffer to write.
+ *
+ * @return number of bytes on success, otherwise negative error code.
+ */
 int
 O2FS_Write(VNode *fn, void *buf, uint64_t off, uint64_t len)
 {
-    NOT_IMPLEMENTED();
-    return -EINVAL;
+    int status;
+    VFS *vfs = fn->vfs;
+    BufCacheEntry *sbEntry = (BufCacheEntry *)vfs->fsptr;
+    SuperBlock *sb = sbEntry->buffer;
+    BufCacheEntry *fileEntry = (BufCacheEntry *)fn->fsptr;
+    BNode *fileBN = fileEntry->buffer;
+    uint64_t blocks = (fileBN->size + sb->blockSize - 1) / sb->blockSize;
+    uint64_t readBytes = 0;
+
+    DLOG(o2fs, "Write %lld %d\n", fileBN->size, blocks);
+
+    // XXX: Check permissions
+
+    if (fileBN->size < (off+len)) {
+	status = O2FSGrowVNode(fn, off+len);
+	if (status < 0)
+	    return status;
+    }
+
+    while (1) {
+	uint64_t b = off / sb->blockSize;
+	uint64_t bOff = off % sb->blockSize;
+	uint64_t bLen;
+	BufCacheEntry *entry;
+
+	if (bOff + len > sb->blockSize) {
+	    bLen = sb->blockSize - bOff;
+	} else {
+	    bLen = len;
+	}
+
+	status = BufCache_Read(fn->disk, fileBN->direct[b].offset, &entry);
+	if (status < 0)
+	    return status;
+
+	DLOG(o2fs, "WRITE %lx %lx %lld\n", buf, entry->buffer, bLen);
+	memcpy(entry->buffer + bOff, buf, bLen);
+	BufCache_Write(entry);
+	BufCache_Release(entry);
+
+	readBytes += bLen;
+	buf += bLen;
+	off += bLen;
+	len -= bLen;
+
+	if (len == 0)
+	    break;
+    }
+
+    return readBytes;
 }
 
+/**
+ * O2FS_ReadDir --
+ *
+ * Read a directory entry.
+ *
+ * @param [in] fn VNode of the directory.
+ * @param [out] buf Buffer to read the directory entry into.
+ * @param [in] len Length of the buffer.
+ * @param [inout] off Offset to start from and return the next offset.
+ *
+ * @return 0 on success, otherwise error.
+ */
 int
 O2FS_ReadDir(VNode *fn, void *buf, uint64_t len, uint64_t *off)
 {
diff --git a/sys/fs/o2fs/o2fs.h b/sys/fs/o2fs/o2fs.h
index 18dd9b9..ce83cf6 100644
--- a/sys/fs/o2fs/o2fs.h
+++ b/sys/fs/o2fs/o2fs.h
@@ -44,13 +44,15 @@ typedef struct ObjID {
  */
 typedef struct SuperBlock
 {
-    uint8_t		magic[8];
-    uint16_t		versionMajor;
-    uint16_t		versionMinor;
+    uint8_t		magic[8];	/* Superblock Magic */
+    uint16_t		versionMajor;	/* Major Version Number */
+    uint16_t		versionMinor;	/* Minor Version Number */
     uint32_t		_rsvd0;
-    uint64_t		features;
-    uint64_t		blockCount;
-    uint64_t		blockSize;
+    uint64_t		features;	/* Feature Flags */
+    uint64_t		blockCount;	/* Total Blocks */
+    uint64_t		blockSize;	/* Block Size in Bytes */
+    uint64_t		bitmapSize;	/* Free Bitmap Size in Bytes */
+    uint64_t		bitmapOffset;	/* Free Bitmap Offset */
 
     uint64_t		version;	/* Snapshot version */
     ObjID		root;		/* Root Tree */
diff --git a/sys/include/vfs.h b/sys/include/vfs.h
index f54bfe0..f55ee9d 100644
--- a/sys/include/vfs.h
+++ b/sys/include/vfs.h
@@ -16,7 +16,9 @@ typedef struct VFS {
     // FS Fields
     void		*fsptr;
     uint64_t		fsval;
+    uint64_t		blksize;
     VNode		*root;
+    void		*bitmap[16];
 } VFS;
 
 typedef struct VNode {
@@ -54,6 +56,7 @@ int VFS_Stat(const char *path, struct stat *sb);
 int VFS_Open(VNode *fn);
 int VFS_Close(VNode *fn);
 int VFS_Read(VNode *fn, void *buf, uint64_t off, uint64_t len);
+int VFS_Write(VNode *fn, void *buf, uint64_t off, uint64_t len);
 int VFS_ReadDir(VNode *fn, void *buf, uint64_t len, uint64_t *off);
 
 #endif /* __SYS_VFS_H__ */
diff --git a/sys/kern/vfsuio.c b/sys/kern/vfsuio.c
index c297b1d..9fb686d 100644
--- a/sys/kern/vfsuio.c
+++ b/sys/kern/vfsuio.c
@@ -29,7 +29,7 @@ VFSUIO_Write(Handle *handle, void *buf, uint64_t len, uint64_t off)
 
     // XXX: Need to pin memory
 
-    return -EINVAL;
+    return VFS_Write(handle->vnode, buf, len, off);
 }
 
 static int
diff --git a/tests/SConscript b/tests/SConscript
index 7bb73d6..95c5a26 100644
--- a/tests/SConscript
+++ b/tests/SConscript
@@ -9,6 +9,12 @@ test_env.Append(CPPFLAGS = ['-fno-builtin', '-nostdinc'])
 test_env.Append(CPPPATH = ['#build/include'])
 test_env.Append(LIBPATH = ['#build/lib/libc'], LIBS = ['c'])
 
+fiotest_src = []
+fiotest_src.append(env["CRTBEGIN"])
+fiotest_src.append(["fiotest.c"])
+fiotest_src.append(env["CRTEND"])
+test_env.Program("fiotest", fiotest_src)
+
 threadtest_src = []
 threadtest_src.append(env["CRTBEGIN"])
 threadtest_src.append(["threadtest.c"])
diff --git a/tests/fiotest.c b/tests/fiotest.c
new file mode 100644
index 0000000..ca9fe41
--- /dev/null
+++ b/tests/fiotest.c
@@ -0,0 +1,28 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+// Castor Only
+#include <syscall.h>
+
+int
+main(int argc, const char *argv[])
+{
+    printf("FIO Test\n");
+    uint64_t fd = OSOpen("/LICENSE", 0);
+
+    for (int i = 0; i < 100; i++) {
+	int status = OSWrite(fd, "123456789\n", i*10, 10);
+	if (status < 0) {
+	    printf("Error: %x\n", -status);
+	    return 1;
+	}
+    }
+
+    printf("Success!\n");
+
+    return 0;
+}
+
diff --git a/tests/spawnanytest.c b/tests/spawnanytest.c
index af8d1f9..a60f0d2 100644
--- a/tests/spawnanytest.c
+++ b/tests/spawnanytest.c
@@ -10,7 +10,7 @@
 int
 main(int argc, const char *argv[])
 {
-    char *program;
+    const char *program;
     int pid[10];
     int status;
 
diff --git a/tests/spawnmultipletest.c b/tests/spawnmultipletest.c
index 8ac5da5..cfbb35c 100644
--- a/tests/spawnmultipletest.c
+++ b/tests/spawnmultipletest.c
@@ -11,7 +11,7 @@ int
 main(int argc, const char *argv[])
 {
     int origpid[10], pid[10];
-    char *program;
+    const char *program;
     int status;
 
     printf("Spawn parallel test wait any: ");
diff --git a/tests/spawnsingletest.c b/tests/spawnsingletest.c
index f4dc097..46c3332 100644
--- a/tests/spawnsingletest.c
+++ b/tests/spawnsingletest.c
@@ -11,7 +11,7 @@ int
 main(int argc, const char *argv[])
 {
     int origpid, pid;
-    char *program;
+    const char *program;
     int status;
 
     printf("Spawn parallel test wait any: ");