diff --git a/drivers/loop/loop.c b/drivers/loop/loop.c
index 01ccee4a9d9..2b2a412b5bd 100644
--- a/drivers/loop/loop.c
+++ b/drivers/loop/loop.c
@@ -40,10 +40,8 @@
  * Private Function Prototypes
  ****************************************************************************/
 
-static ssize_t loop_readv(FAR struct file *filep,
-                          FAR const struct uio *uio);
-static ssize_t loop_writev(FAR struct file *filep,
-                           FAR const struct uio *uio);
+static ssize_t loop_readv(FAR struct file *filep, FAR struct uio *uio);
+static ssize_t loop_writev(FAR struct file *filep, FAR struct uio *uio);
 static int     loop_ioctl(FAR struct file *filep, int cmd,
                  unsigned long arg);
 
@@ -74,8 +72,7 @@ static const struct file_operations g_loop_fops =
  * Name: loop_readv
  ****************************************************************************/
 
-static ssize_t loop_readv(FAR struct file *filep,
-                          FAR const struct uio *uio)
+static ssize_t loop_readv(FAR struct file *filep, FAR struct uio *uio)
 {
   return 0; /* Return EOF */
 }
@@ -84,10 +81,14 @@ static ssize_t loop_readv(FAR struct file *filep,
  * Name: loop_writev
  ****************************************************************************/
 
-static ssize_t loop_writev(FAR struct file *filep,
-                           FAR const struct uio *uio)
+static ssize_t loop_writev(FAR struct file *filep, FAR struct uio *uio)
 {
-  return uio_total_len(uio); /* Say that everything was written */
+  /* Say that everything was written */
+
+  size_t ret = uio->uio_resid;
+
+  uio_advance(uio, ret);
+  return ret;
 }
 
 /****************************************************************************
diff --git a/drivers/misc/dev_null.c b/drivers/misc/dev_null.c
index da37ddbf8ec..0c196fc7c71 100644
--- a/drivers/misc/dev_null.c
+++ b/drivers/misc/dev_null.c
@@ -40,10 +40,8 @@
  * Private Function Prototypes
  ****************************************************************************/
 
-static ssize_t devnull_readv(FAR struct file *filep,
-                             FAR const struct uio *uio);
-static ssize_t devnull_writev(FAR struct file *filep,
-                              FAR const struct uio *uio);
+static ssize_t devnull_readv(FAR struct file *filep, FAR struct uio *uio);
+static ssize_t devnull_writev(FAR struct file *filep, FAR struct uio *uio);
 static int     devnull_poll(FAR struct file *filep, FAR struct pollfd *fds,
                             bool setup);
 
@@ -74,8 +72,7 @@ static const struct file_operations g_devnull_fops =
  * Name: devnull_readv
  ****************************************************************************/
 
-static ssize_t devnull_readv(FAR struct file *filep,
-                             FAR const struct uio *uio)
+static ssize_t devnull_readv(FAR struct file *filep, FAR struct uio *uio)
 {
   UNUSED(filep);
   UNUSED(uio);
@@ -87,12 +84,16 @@ static ssize_t devnull_readv(FAR struct file *filep,
  * Name: devnull_writev
  ****************************************************************************/
 
-static ssize_t devnull_writev(FAR struct file *filep,
-                              FAR const struct uio *uio)
+static ssize_t devnull_writev(FAR struct file *filep, FAR struct uio *uio)
 {
   UNUSED(filep);
 
-  return uio_total_len(uio); /* Say that everything was written */
+  /* Say that everything was written */
+
+  size_t ret = uio->uio_resid;
+
+  uio_advance(uio, ret);
+  return ret;
 }
 
 /****************************************************************************
diff --git a/drivers/misc/dev_zero.c b/drivers/misc/dev_zero.c
index 1ea18e9d982..38be2fd9fcc 100644
--- a/drivers/misc/dev_zero.c
+++ b/drivers/misc/dev_zero.c
@@ -40,10 +40,8 @@
  * Private Function Prototypes
  ****************************************************************************/
 
-static ssize_t devzero_readv(FAR struct file *filep,
-                             FAR const struct uio *uio);
-static ssize_t devzero_writev(FAR struct file *filep,
-                              FAR const struct uio *uio);
+static ssize_t devzero_readv(FAR struct file *filep, FAR struct uio *uio);
+static ssize_t devzero_writev(FAR struct file *filep, FAR struct uio *uio);
 static int     devzero_poll(FAR struct file *filep, FAR struct pollfd *fds,
                             bool setup);
 
@@ -74,26 +72,22 @@ static const struct file_operations g_devzero_fops =
  * Name: devzero_readv
  ****************************************************************************/
 
-static ssize_t devzero_readv(FAR struct file *filep,
-                             FAR const struct uio *uio)
+static ssize_t devzero_readv(FAR struct file *filep, FAR struct uio *uio)
 {
-  ssize_t total =  uio_total_len(uio);
+  size_t total = uio->uio_resid;
   FAR const struct iovec *iov = uio->uio_iov;
   int iovcnt = uio->uio_iovcnt;
   int i;
 
   UNUSED(filep);
 
-  if (total < 0)
-    {
-      return total;
-    }
-
   for (i = 0; i < iovcnt; i++)
     {
       memset(iov[i].iov_base, 0, iov[i].iov_len);
     }
 
+  uio_advance(uio, total);
+
   return total;
 }
 
@@ -101,12 +95,15 @@ static ssize_t devzero_readv(FAR struct file *filep,
  * Name: devzero_writev
  ****************************************************************************/
 
-static ssize_t devzero_writev(FAR struct file *filep,
-                              FAR const struct uio *uio)
+static ssize_t devzero_writev(FAR struct file *filep, FAR struct uio *uio)
 {
+  size_t total;
   UNUSED(filep);
 
-  return uio_total_len(uio);
+  total = uio->uio_resid;
+
+  uio_advance(uio, total);
+  return total;
 }
 
 /****************************************************************************
diff --git a/fs/vfs/fs_read.c b/fs/vfs/fs_read.c
index fce68e0d68b..1d93af0e04b 100644
--- a/fs/vfs/fs_read.c
+++ b/fs/vfs/fs_read.c
@@ -50,8 +50,7 @@
  *
  ****************************************************************************/
 
-static ssize_t file_readv_compat(FAR struct file *filep,
-                                 FAR const struct uio *uio)
+static ssize_t file_readv_compat(FAR struct file *filep, FAR struct uio *uio)
 {
   FAR const struct iovec *iov = uio->uio_iov;
   int iovcnt = uio->uio_iovcnt;
@@ -102,6 +101,11 @@ static ssize_t file_readv_compat(FAR struct file *filep,
       remaining -= nread;
     }
 
+  if (ntotal >= 0)
+    {
+      uio_advance(uio, ntotal);
+    }
+
   return ntotal;
 }
 
@@ -130,7 +134,7 @@ static ssize_t file_readv_compat(FAR struct file *filep,
  *
  ****************************************************************************/
 
-ssize_t file_readv(FAR struct file *filep, FAR const struct uio *uio)
+ssize_t file_readv(FAR struct file *filep, FAR struct uio *uio)
 {
   FAR struct inode *inode;
   ssize_t ret = -EBADF;
@@ -204,11 +208,16 @@ ssize_t file_read(FAR struct file *filep, FAR void *buf, size_t nbytes)
 {
   struct iovec iov;
   struct uio uio;
+  ssize_t ret;
 
   iov.iov_base = buf;
   iov.iov_len = nbytes;
-  uio.uio_iov = &iov;
-  uio.uio_iovcnt = 1;
+  ret = uio_init(&uio, &iov, 1);
+  if (ret != 0)
+    {
+      return ret;
+    }
+
   return file_readv(filep, &uio);
 }
 
@@ -251,9 +260,12 @@ ssize_t nx_readv(int fd, FAR const struct iovec *iov, int iovcnt)
 
   /* Then let file_readv do all of the work. */
 
-  uio.uio_iov = iov;
-  uio.uio_iovcnt = iovcnt;
-  ret = file_readv(filep, &uio);
+  ret = uio_init(&uio, iov, iovcnt);
+  if (ret == 0)
+    {
+      ret = file_readv(filep, &uio);
+    }
+
   fs_putfilep(filep);
   return ret;
 }
diff --git a/fs/vfs/fs_uio.c b/fs/vfs/fs_uio.c
index 5c6e260d559..0ee178bfbfe 100644
--- a/fs/vfs/fs_uio.c
+++ b/fs/vfs/fs_uio.c
@@ -35,19 +35,19 @@
 #include <errno.h>
 
 /****************************************************************************
- * Public Functions
+ * Private Functions
  ****************************************************************************/
 
 /****************************************************************************
- * Name: uio_total_len
+ * Name: uio_calc_resid
  *
  * Description:
- *   Return the total length of data in bytes.
- *   Or -EOVERFLOW.
+ *   Return the remaining length of data in bytes.
+ *   Or -EINVAL.
  *
  ****************************************************************************/
 
-ssize_t uio_total_len(FAR const struct uio *uio)
+ssize_t uio_calc_resid(FAR const struct uio *uio)
 {
   const struct iovec *iov = uio->uio_iov;
   int iovcnt = uio->uio_iovcnt;
@@ -58,7 +58,7 @@ ssize_t uio_total_len(FAR const struct uio *uio)
     {
       if (SSIZE_MAX - len < iov[i].iov_len)
         {
-          return -EOVERFLOW;
+          return -EINVAL;
         }
 
       len += iov[i].iov_len;
@@ -66,3 +66,164 @@ ssize_t uio_total_len(FAR const struct uio *uio)
 
   return len;
 }
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: uio_advance
+ *
+ * Description:
+ *   Advance the pointer/offset in uio by the specified amount.
+ *
+ ****************************************************************************/
+
+void uio_advance(FAR struct uio *uio, size_t sz)
+{
+  FAR const struct iovec *iov = uio->uio_iov;
+  int iovcnt = uio->uio_iovcnt;
+  size_t offset_in_iov = uio->uio_offset_in_iov;
+
+  DEBUGASSERT(sz <= SSIZE_MAX);
+  DEBUGASSERT(uio->uio_resid <= SSIZE_MAX);
+  DEBUGASSERT(sz <= uio->uio_resid);
+  DEBUGASSERT(uio->uio_offset_in_iov + uio->uio_resid ==
+              uio_calc_resid(uio));
+  uio->uio_resid -= sz;
+  while (iovcnt > 0)
+    {
+      DEBUGASSERT(offset_in_iov <= iov->iov_len);
+      if (sz < iov->iov_len - offset_in_iov)
+        {
+          offset_in_iov += sz;
+          break;
+        }
+
+      sz -= iov->iov_len - offset_in_iov;
+      iov++;
+      iovcnt--;
+      offset_in_iov = 0;
+    }
+
+  uio->uio_iov = iov;
+  uio->uio_iovcnt = iovcnt;
+  uio->uio_offset_in_iov = offset_in_iov;
+  DEBUGASSERT(uio->uio_offset_in_iov + uio->uio_resid ==
+              uio_calc_resid(uio));
+}
+
+/****************************************************************************
+ * Name: uio_init
+ *
+ * Description:
+ *   Initialize the uio structure with reasonable default values.
+ *
+ ****************************************************************************/
+
+int uio_init(FAR struct uio *uio, FAR const struct iovec *iov, int iovcnt)
+{
+  ssize_t resid;
+
+  memset(uio, 0, sizeof(*uio));
+  uio->uio_iov = iov;
+  uio->uio_iovcnt = iovcnt;
+  resid = uio_calc_resid(uio);
+  if (resid < 0)
+    {
+      return -EINVAL;
+    }
+
+  uio->uio_resid = resid;
+  return 0;
+}
+
+/****************************************************************************
+ * Name: uio_copyfrom
+ *
+ * Description:
+ *   Copy data from the linear buffer to uio.
+ *
+ ****************************************************************************/
+
+void uio_copyfrom(FAR struct uio *uio, size_t offset, FAR const void *buf,
+                  size_t len)
+{
+  FAR const struct iovec *iov = uio->uio_iov;
+
+  DEBUGASSERT(uio->uio_resid >= 0);
+  DEBUGASSERT(uio->uio_resid <= SSIZE_MAX);
+  DEBUGASSERT(len <= uio->uio_resid);
+  DEBUGASSERT(offset <= uio->uio_resid - len);
+  DEBUGASSERT(SSIZE_MAX - offset >= uio->uio_offset_in_iov);
+  DEBUGASSERT(uio->uio_offset_in_iov + uio->uio_resid ==
+              uio_calc_resid(uio));
+
+  offset += uio->uio_offset_in_iov;
+  while (offset > iov->iov_len)
+    {
+      offset -= iov->iov_len;
+      iov++;
+    }
+
+  while (len > 0)
+    {
+      size_t blen = len;
+      if (blen > iov->iov_len - offset)
+        {
+          blen = iov->iov_len - offset;
+        }
+
+      memcpy((FAR uint8_t *)iov->iov_base + offset, buf, blen);
+
+      len -= blen;
+      buf = (const uint8_t *)buf + blen;
+      iov++;
+      offset = 0;
+    }
+}
+
+/****************************************************************************
+ * Name: uio_copyto
+ *
+ * Description:
+ *   Copy data to the linear buffer from uio.
+ *
+ ****************************************************************************/
+
+void uio_copyto(FAR struct uio *uio, size_t offset, FAR void *buf,
+                size_t len)
+{
+  FAR const struct iovec *iov = uio->uio_iov;
+
+  DEBUGASSERT(uio->uio_resid >= 0);
+  DEBUGASSERT(uio->uio_resid <= SSIZE_MAX);
+  DEBUGASSERT(len <= uio->uio_resid);
+  DEBUGASSERT(offset <= uio->uio_resid - len);
+  DEBUGASSERT(SSIZE_MAX - offset >= uio->uio_offset_in_iov);
+  DEBUGASSERT(uio->uio_offset_in_iov + uio->uio_resid ==
+              uio_calc_resid(uio));
+
+  offset += uio->uio_offset_in_iov;
+  while (offset > iov->iov_len)
+    {
+      offset -= iov->iov_len;
+      iov++;
+    }
+
+  while (len > 0)
+    {
+      size_t blen = len;
+      if (blen > iov->iov_len - offset)
+        {
+          blen = iov->iov_len - offset;
+        }
+
+      memcpy(buf, (FAR const uint8_t *)iov->iov_base + offset, blen);
+
+      len -= blen;
+      buf = (uint8_t *)buf + blen;
+      iov++;
+      offset = 0;
+    }
+}
diff --git a/fs/vfs/fs_write.c b/fs/vfs/fs_write.c
index 39f49517bea..16be9ea957f 100644
--- a/fs/vfs/fs_write.c
+++ b/fs/vfs/fs_write.c
@@ -51,7 +51,7 @@
  ****************************************************************************/
 
 static ssize_t file_writev_compat(FAR struct file *filep,
-                                  FAR const struct uio *uio)
+                                  FAR struct uio *uio)
 {
   FAR const struct iovec *iov = uio->uio_iov;
   int iovcnt = uio->uio_iovcnt;
@@ -102,6 +102,11 @@ static ssize_t file_writev_compat(FAR struct file *filep,
       remaining -= nwritten;
     }
 
+  if (ntotal >= 0)
+    {
+      uio_advance(uio, ntotal);
+    }
+
   return ntotal;
 }
 
@@ -133,7 +138,7 @@ static ssize_t file_writev_compat(FAR struct file *filep,
  *
  ****************************************************************************/
 
-ssize_t file_writev(FAR struct file *filep, FAR const struct uio *uio)
+ssize_t file_writev(FAR struct file *filep, FAR struct uio *uio)
 {
   FAR struct inode *inode;
   ssize_t ret = -EBADF;
@@ -202,11 +207,16 @@ ssize_t file_write(FAR struct file *filep, FAR const void *buf,
 {
   struct iovec iov;
   struct uio uio;
+  ssize_t ret;
 
   iov.iov_base = (FAR void *)buf;
   iov.iov_len = nbytes;
-  uio.uio_iov = &iov;
-  uio.uio_iovcnt = 1;
+  ret = uio_init(&uio, &iov, 1);
+  if (ret != 0)
+    {
+      return ret;
+    }
+
   return file_writev(filep, &uio);
 }
 
@@ -252,9 +262,12 @@ ssize_t nx_writev(int fd, FAR const struct iovec *iov, int iovcnt)
        * index.  Note that file_writev() will return the errno on failure.
        */
 
-      uio.uio_iov = iov;
-      uio.uio_iovcnt = iovcnt;
-      ret = file_writev(filep, &uio);
+      ret = uio_init(&uio, iov, iovcnt);
+      if (ret == 0)
+        {
+          ret = file_writev(filep, &uio);
+        }
+
       fs_putfilep(filep);
     }
 
diff --git a/include/nuttx/fs/fs.h b/include/nuttx/fs/fs.h
index ed9731683f3..72edf64d655 100644
--- a/include/nuttx/fs/fs.h
+++ b/include/nuttx/fs/fs.h
@@ -240,8 +240,8 @@ struct file_operations
 
   CODE int     (*poll)(FAR struct file *filep, FAR struct pollfd *fds,
                        bool setup);
-  CODE ssize_t (*readv)(FAR struct file *filep, FAR const struct uio *uio);
-  CODE ssize_t (*writev)(FAR struct file *filep, FAR const struct uio *uio);
+  CODE ssize_t (*readv)(FAR struct file *filep, FAR struct uio *uio);
+  CODE ssize_t (*writev)(FAR struct file *filep, FAR struct uio *uio);
 
   /* The two structures need not be common after this point */
 
@@ -311,8 +311,8 @@ struct mountpt_operations
   CODE int     (*truncate)(FAR struct file *filep, off_t length);
   CODE int     (*poll)(FAR struct file *filep, FAR struct pollfd *fds,
                        bool setup);
-  CODE ssize_t (*readv)(FAR struct file *filep, FAR const struct uio *uio);
-  CODE ssize_t (*writev)(FAR struct file *filep, FAR const struct uio *uio);
+  CODE ssize_t (*readv)(FAR struct file *filep, FAR struct uio *uio);
+  CODE ssize_t (*writev)(FAR struct file *filep, FAR struct uio *uio);
 
   /* The two structures need not be common after this point. The following
    * are extended methods needed to deal with the unique needs of mounted
@@ -1419,7 +1419,7 @@ int close_mtddriver(FAR struct inode *pinode);
  ****************************************************************************/
 
 ssize_t file_read(FAR struct file *filep, FAR void *buf, size_t nbytes);
-ssize_t file_readv(FAR struct file *filep, FAR const struct uio *uio);
+ssize_t file_readv(FAR struct file *filep, FAR struct uio *uio);
 
 /****************************************************************************
  * Name: nx_read
@@ -1473,7 +1473,7 @@ ssize_t nx_readv(int fd, FAR const struct iovec *iov, int iovcnt);
 
 ssize_t file_write(FAR struct file *filep, FAR const void *buf,
                    size_t nbytes);
-ssize_t file_writev(FAR struct file *filep, FAR const struct uio *uio);
+ssize_t file_writev(FAR struct file *filep, FAR struct uio *uio);
 
 /****************************************************************************
  * Name: nx_write
diff --git a/include/nuttx/fs/uio.h b/include/nuttx/fs/uio.h
index e864745a18c..91e84a7a6c2 100644
--- a/include/nuttx/fs/uio.h
+++ b/include/nuttx/fs/uio.h
@@ -45,6 +45,12 @@ struct uio
 {
   FAR const struct iovec *uio_iov;
   int uio_iovcnt;
+  size_t uio_resid;         /* the remaining bytes in the request */
+  size_t uio_offset_in_iov; /* offset in uio_iov[0].iov_base */
+
+#if 0 /* notyet; planned for pread/pwrite */
+  off_t uio_offset;         /* offset in the file */
+#endif
 };
 
 /****************************************************************************
@@ -52,14 +58,52 @@ struct uio
  ****************************************************************************/
 
 /****************************************************************************
- * Name: uio_total_len
+ * Name: uio_advance
  *
  * Description:
- *   Return the total length of data in bytes.
- *   Or -EOVERFLOW.
+ *   Advance the pointer/offset in uio by the specified amount.
  *
  ****************************************************************************/
 
-ssize_t uio_total_len(FAR const struct uio *uio);
+void uio_advance(FAR struct uio *uio, size_t sz);
+
+/****************************************************************************
+ * Name: uio_init
+ *
+ * Description:
+ *   Initialize the uio structure with reasonable default values.
+ *
+ * Return Value:
+ *   0 on success. A negative error number on an error.
+ *
+ *   -EINVAL: The total size of the given iovec is too large.
+ *            (Note: NetBSD's readv returns EINVAL in that case.
+ *            I (yamamoto) couldn't find the specification in POSIX.)
+ *
+ ****************************************************************************/
+
+int uio_init(FAR struct uio *uio, FAR const struct iovec *iov, int iovcnt);
+
+/****************************************************************************
+ * Name: uio_copyto
+ *
+ * Description:
+ *   Copy data to the linear buffer from uio.
+ *
+ ****************************************************************************/
+
+void uio_copyfrom(FAR struct uio *uio, size_t offset, FAR const void *buf,
+                  size_t len);
+
+/****************************************************************************
+ * Name: uio_copyto
+ *
+ * Description:
+ *   Copy data to the linear buffer from uio.
+ *
+ ****************************************************************************/
+
+void uio_copyto(FAR struct uio *uio, size_t offset, FAR void *buf,
+                size_t len);
 
 #endif /* __INCLUDE_NUTTX_FS_UIO_H */