[Qemu-devel] [PATCHv4 11/11] rewrite iov_send_recv() and move it to iov.c

[Michael Tokarev]

Make it much more understandable, add a missing
iov_cnt argument (number of iovs in the iov), and
add comments to it.

The new implementation has been extensively tested
by splitting a large buffer into many small
randomly-sized chunks, sending it over socket to
another, slow process and verifying the receiving
data is the same.

Signed-off-by: Michael Tokarev <address@hidden>
---
 cutils.c            |   83 ----------------------------------------
 iov.c               |  105 +++++++++++++++++++++++++++++++++++++++++++++++++++
 iov.h               |   15 ++++---
 qemu-coroutine-io.c |    2 +-
 4 files changed, 115 insertions(+), 90 deletions(-)

diff --git a/cutils.c b/cutils.c
index cb6f638..e2bc1b8 100644
--- a/cutils.c
+++ b/cutils.c
@@ -375,86 +375,3 @@ int qemu_parse_fd(const char *param)
     }
     return fd;
 }
-
-ssize_t iov_send_recv(int sockfd, struct iovec *iov,
-                      size_t offset, size_t bytes,
-                      bool do_sendv)
-{
-    int iovlen;
-    ssize_t ret;
-    size_t diff;
-    struct iovec *last_iov;
-
-    /* last_iov is inclusive, so count from one.  */
-    iovlen = 1;
-    last_iov = iov;
-    bytes += offset;
-
-    while (last_iov->iov_len < bytes) {
-        bytes -= last_iov->iov_len;
-
-        last_iov++;
-        iovlen++;
-    }
-
-    diff = last_iov->iov_len - bytes;
-    last_iov->iov_len -= diff;
-
-    while (iov->iov_len <= offset) {
-        offset -= iov->iov_len;
-
-        iov++;
-        iovlen--;
-    }
-
-    iov->iov_base = (char *) iov->iov_base + offset;
-    iov->iov_len -= offset;
-
-    {
-#if defined CONFIG_IOVEC && defined CONFIG_POSIX
-        struct msghdr msg;
-        memset(&msg, 0, sizeof(msg));
-        msg.msg_iov = iov;
-        msg.msg_iovlen = iovlen;
-
-        do {
-            if (do_sendv) {
-                ret = sendmsg(sockfd, &msg, 0);
-            } else {
-                ret = recvmsg(sockfd, &msg, 0);
-            }
-        } while (ret == -1 && errno == EINTR);
-#else
-        struct iovec *p = iov;
-        ret = 0;
-        while (iovlen > 0) {
-            int rc;
-            if (do_sendv) {
-                rc = send(sockfd, p->iov_base, p->iov_len, 0);
-            } else {
-                rc = qemu_recv(sockfd, p->iov_base, p->iov_len, 0);
-            }
-            if (rc == -1) {
-                if (errno == EINTR) {
-                    continue;
-                }
-                if (ret == 0) {
-                    ret = -1;
-                }
-                break;
-            }
-            if (rc == 0) {
-                break;
-            }
-            ret += rc;
-            iovlen--, p++;
-        }
-#endif
-    }
-
-    /* Undo the changes above */
-    iov->iov_base = (char *) iov->iov_base - offset;
-    iov->iov_len += offset;
-    last_iov->iov_len += diff;
-    return ret;
-}
diff --git a/iov.c b/iov.c
index fd518dd..6c79b68 100644
--- a/iov.c
+++ b/iov.c
@@ -18,6 +18,14 @@
 
 #include "iov.h"
 
+#ifdef _WIN32
+# include <windows.h>
+# include <winsock2.h>
+#else
+# include <sys/types.h>
+# include <sys/socket.h>
+#endif
+
 size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
                     size_t offset, const void *buf, size_t bytes)
 {
@@ -87,6 +95,103 @@ size_t iov_size(const struct iovec *iov, const unsigned int 
iov_cnt)
     return len;
 }
 
+/* helper function for iov_send_recv() */
+static ssize_t
+do_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, bool do_send)
+{
+#if defined CONFIG_IOVEC && defined CONFIG_POSIX
+    ssize_t ret;
+    struct msghdr msg;
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_iov = iov;
+    msg.msg_iovlen = iov_cnt;
+    do {
+        ret = do_send
+            ? sendmsg(sockfd, &msg, 0)
+            : recvmsg(sockfd, &msg, 0);
+    } while (ret < 0 && errno == EINTR);
+    return ret;
+#else
+    /* else send piece-by-piece */
+    /*XXX Note: windows has WSASend() and WSARecv() */
+    unsigned i;
+    size_t count = 0;
+    for(i = 0; i < iov_cnt; ++i) {
+        ssize_t r = do_send
+            ? send(sockfd, iov[i].iov_base, iov[i].iov_len, 0)
+            : recv(sockfd, iov[i].iov_base, iov[i].iov_len, 0);
+        if (r > 0) {
+            ret += r;
+        } else if (!r) {
+            break;
+        } else if (errno == EINTR) {
+            continue;
+        } else {
+            /* else it is some "other" error,
+             * only return if there was no data processed. */
+            if (ret == 0) {
+                return -1;
+            }
+            break;
+        }
+    }
+    return count;
+#endif
+}
+
+ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
+                      size_t offset, size_t bytes,
+                      bool do_send)
+{
+    ssize_t ret;
+    size_t lastlen;
+    unsigned si, ei;            /* start and end indexes */
+
+    /* Find the start position, skipping `offset' bytes:
+     * first, skip all full-sized vector elements, */
+    for(si = 0; si < iov_cnt && offset >= iov[si].iov_len; ++si) {
+        offset -= iov[si].iov_len;
+    }
+    if (offset) {
+        assert(si < iov_cnt);
+        /* second, skip `offset' bytes from the (now) first element,
+         * undo it on exit */
+        iov[si].iov_base += offset;
+        iov[si].iov_len -= offset;
+    }
+    /* Find the end position skipping `bytes' bytes: */
+    /* first, skip all full-sized elements */
+    for(ei = si; ei < iov_cnt && iov[ei].iov_len <= bytes; ++ei) {
+        bytes -= iov[ei].iov_len;
+    }
+    if (bytes) {
+        /* second, fixup the last element, and remember
+         * the length we've cut from the end of it in `bytes' */
+        assert(ei < iov_cnt);
+        assert(iov[ei].iov_len > bytes);
+        lastlen = iov[ei].iov_len;
+        iov[ei].iov_len = bytes;
+        ++ei;
+    } else {
+        lastlen = 0;
+    }
+
+    ret = do_send_recv(sockfd, iov + si, ei - si, do_send);
+
+    /* Undo the changes above */
+    if (offset) {
+        iov[si].iov_base -= offset;
+        iov[si].iov_len += offset;
+    }
+    if (lastlen) {
+        --ei;
+        iov[ei].iov_len = lastlen;
+    }
+
+    return ret;
+}
+
+
 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
                  FILE *fp, const char *prefix, size_t limit)
 {
diff --git a/iov.h b/iov.h
index 9b6a883..381f37a 100644
--- a/iov.h
+++ b/iov.h
@@ -60,7 +60,7 @@ size_t iov_memset(const struct iovec *iov, const unsigned int 
iov_cnt,
  * `offset' bytes in the beginning of iovec buffer are skipped and
  * next `bytes' bytes are used, which must be within data of iovec.
  *
- *   r = iov_send_recv(sockfd, iov, offset, bytes, true);
+ *   r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
  *
  * is logically equivalent to
  *
@@ -68,13 +68,16 @@ size_t iov_memset(const struct iovec *iov, const unsigned 
int iov_cnt,
  *   iov_to_buf(iov, iovcnt, offset, buf, bytes);
  *   r = send(sockfd, buf, bytes, 0);
  *   free(buf);
+ *
+ * For iov_send_recv() _whole_ area being sent or received
+ * should be within the iovec, not only beginning of it.
  */
-ssize_t iov_send_recv(int sockfd, struct iovec *iov,
+ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
                       size_t offset, size_t bytes, bool do_send);
-#define iov_recv(sockfd, iov, offset, bytes) \
-  iov_send_recv(sockfd, iov, offset, bytes, false)
-#define iov_send(sockfd, iov, offset, bytes) \
-  iov_send_recv(sockfd, iov, offset, bytes, true)
+#define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
+  iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
+#define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
+  iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
 
 /**
  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
diff --git a/qemu-coroutine-io.c b/qemu-coroutine-io.c
index 6693c78..5734965 100644
--- a/qemu-coroutine-io.c
+++ b/qemu-coroutine-io.c
@@ -34,7 +34,7 @@ qemu_co_sendv_recvv(int sockfd, struct iovec *iov, unsigned 
iov_cnt,
     size_t done = 0;
     ssize_t ret;
     while (done < bytes) {
-        ret = iov_send_recv(sockfd, iov,
+        ret = iov_send_recv(sockfd, iov, iov_cnt,
                             offset + done, bytes - done, do_send);
         if (ret > 0) {
             done += ret;
-- 
1.7.9.1