diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index eb22d04..8128b64 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -1783,7 +1783,7 @@
         if (iov) {
             buf2_size = iov_size(iov, 3);
             buf2 = g_malloc(buf2_size);
-            iov_to_buf(iov, 3, buf2, 0, buf2_size);
+            iov_to_buf(iov, 3, 0, buf2, buf2_size);
             buf = buf2;
         }
 
diff --git a/hw/usb/core.c b/hw/usb/core.c
index 0e02da7..2641685 100644
--- a/hw/usb/core.c
+++ b/hw/usb/core.c
@@ -522,10 +522,10 @@
     switch (p->pid) {
     case USB_TOKEN_SETUP:
     case USB_TOKEN_OUT:
-        iov_to_buf(p->iov.iov, p->iov.niov, ptr, p->result, bytes);
+        iov_to_buf(p->iov.iov, p->iov.niov, p->result, ptr, bytes);
         break;
     case USB_TOKEN_IN:
-        iov_from_buf(p->iov.iov, p->iov.niov, ptr, p->result, bytes);
+        iov_from_buf(p->iov.iov, p->iov.niov, p->result, ptr, bytes);
         break;
     default:
         fprintf(stderr, "%s: invalid pid: %x\n", __func__, p->pid);
@@ -539,7 +539,7 @@
     assert(p->result >= 0);
     assert(p->result + bytes <= p->iov.size);
     if (p->pid == USB_TOKEN_IN) {
-        iov_clear(p->iov.iov, p->iov.niov, p->result, bytes);
+        iov_memset(p->iov.iov, p->iov.niov, p->result, 0, bytes);
     }
     p->result += bytes;
 }
diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index 075ed87..23effa4 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -77,7 +77,7 @@
         size_t offset = 0;
         uint32_t pfn;
 
-        while (iov_to_buf(elem.out_sg, elem.out_num, &pfn, offset, 4) == 4) {
+        while (iov_to_buf(elem.out_sg, elem.out_num, offset, &pfn, 4) == 4) {
             ram_addr_t pa;
             ram_addr_t addr;
 
@@ -118,7 +118,7 @@
      */
     reset_stats(s);
 
-    while (iov_to_buf(elem->out_sg, elem->out_num, &stat, offset, sizeof(stat))
+    while (iov_to_buf(elem->out_sg, elem->out_num, offset, &stat, sizeof(stat))
            == sizeof(stat)) {
         uint16_t tag = tswap16(stat.tag);
         uint64_t val = tswap64(stat.val);
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index 3f190d4..533aa3d 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -656,8 +656,8 @@
         }
 
         /* copy in packet.  ugh */
-        len = iov_from_buf(sg, elem.in_num,
-                           buf + offset, 0, size - offset);
+        len = iov_from_buf(sg, elem.in_num, 0,
+                           buf + offset, size - offset);
         total += len;
         offset += len;
         /* If buffers can't be merged, at this point we
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index 1e477e5..728f218 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -106,8 +106,8 @@
             break;
         }
 
-        len = iov_from_buf(elem.in_sg, elem.in_num,
-                           buf + offset, 0, size - offset);
+        len = iov_from_buf(elem.in_sg, elem.in_num, 0,
+                           buf + offset, size - offset);
         offset += len;
 
         virtqueue_push(vq, &elem, len);
@@ -467,7 +467,7 @@
             buf = g_malloc(cur_len);
             len = cur_len;
         }
-        iov_to_buf(elem.out_sg, elem.out_num, buf, 0, cur_len);
+        iov_to_buf(elem.out_sg, elem.out_num, 0, buf, cur_len);
 
         handle_control_message(vser, buf, cur_len);
         virtqueue_push(vq, &elem, 0);
diff --git a/iov.c b/iov.c
index 0f96493..bc58cab 100644
--- a/iov.c
+++ b/iov.c
@@ -17,8 +17,8 @@
 
 #include "iov.h"
 
-size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
-                    const void *buf, size_t iov_off, size_t size)
+size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt, size_t iov_off,
+                    const void *buf, size_t size)
 {
     size_t iovec_off, buf_off;
     unsigned int i;
@@ -40,8 +40,8 @@
     return buf_off;
 }
 
-size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
-                  void *buf, size_t iov_off, size_t size)
+size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt, size_t iov_off,
+                  void *buf, size_t size)
 {
     uint8_t *ptr;
     size_t iovec_off, buf_off;
@@ -65,8 +65,8 @@
     return buf_off;
 }
 
-size_t iov_clear(const struct iovec *iov, const unsigned int iov_cnt,
-                 size_t iov_off, size_t size)
+size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
+                 size_t iov_off, int fillc, size_t size)
 {
     size_t iovec_off, buf_off;
     unsigned int i;
@@ -77,7 +77,7 @@
         if (iov_off < (iovec_off + iov[i].iov_len)) {
             size_t len = MIN((iovec_off + iov[i].iov_len) - iov_off , size);
 
-            memset(iov[i].iov_base + (iov_off - iovec_off), 0, len);
+            memset(iov[i].iov_base + (iov_off - iovec_off), fillc, len);
 
             buf_off += len;
             iov_off += len;
diff --git a/iov.h b/iov.h
index 94d2f78..0b4acf4 100644
--- a/iov.h
+++ b/iov.h
@@ -12,12 +12,44 @@
 
 #include "qemu-common.h"
 
-size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
-                    const void *buf, size_t iov_off, size_t size);
-size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
-                  void *buf, size_t iov_off, size_t size);
+/**
+ * count and return data size, in bytes, of an iovec
+ * starting at `iov' of `iov_cnt' number of elements.
+ */
 size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
-size_t iov_clear(const struct iovec *iov, const unsigned int iov_cnt,
-                 size_t iov_off, size_t size);
+
+/**
+ * Copy from single continuous buffer to scatter-gather vector of buffers
+ * (iovec) and back like memcpy() between two continuous memory regions.
+ * Data in single continuous buffer starting at address `buf' and
+ * `bytes' bytes long will be copied to/from an iovec `iov' with
+ * `iov_cnt' number of elements, starting at byte position `offset'
+ * within the iovec.  If the iovec does not contain enough space,
+ * only part of data will be copied, up to the end of the iovec.
+ * Number of bytes actually copied will be returned, which is
+ *  min(bytes, iov_size(iov)-offset)
+ */
+size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
+                    size_t offset, const void *buf, size_t bytes);
+size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
+                  size_t offset, void *buf, size_t bytes);
+
+/**
+ * Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
+ * starting at byte offset `start', to value `fillc', repeating it
+ * `bytes' number of times.
+ * If `bytes' is large enough, only last bytes portion of iovec,
+ * up to the end of it, will be filled with the specified value.
+ * Function return actual number of bytes processed, which is
+ * min(size, iov_size(iov) - offset).
+ */
+size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
+                  size_t offset, int fillc, size_t bytes);
+
+/**
+ * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
+ * in file `fp', prefixing each line with `prefix' and processing not more
+ * than `limit' data bytes.
+ */
 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
                  FILE *fp, const char *prefix, size_t limit);
diff --git a/net.c b/net.c
index 4aa416c..abf0fd0 100644
--- a/net.c
+++ b/net.c
@@ -544,7 +544,7 @@
     uint8_t buffer[4096];
     size_t offset;
 
-    offset = iov_to_buf(iov, iovcnt, buffer, 0, sizeof(buffer));
+    offset = iov_to_buf(iov, iovcnt, 0, buffer, sizeof(buffer));
 
     return vc->info->receive(vc, buffer, offset);
 }