win32: add readv/writev emulation

Commit e9d8fbf (qemu-file: do not use stdio for qemu_fdopen, 2013-03-27)
introduced a usage of writev, which mingw32 does not have.  Even though
qemu_fdopen itself is not used on mingw32, the future-proof solution is
to add an implementation of it.  This is simple and similar to how we
emulate sendmsg/recvmsg in util/iov.c.

Some files include osdep.h without qemu-common.h, so move the definition
of iovec to osdep.h too, and include osdep.h from qemu-common.h
unconditionally (protection against including files when NEED_CPU_H is
defined is not needed since the removal of AREG0).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu-common.h

@@ -84,20 +84,6 @@
 # error Unknown pointer size
 #endif
 
-#ifndef CONFIG_IOVEC
-#define CONFIG_IOVEC
-struct iovec {
-    void *iov_base;
-    size_t iov_len;
-};
-/*
- * Use the same value as Linux for now.
- */
-#define IOV_MAX		1024
-#else
-#include <sys/uio.h>
-#endif
-
 typedef int (*fprintf_function)(FILE *f, const char *fmt, ...)
     GCC_FMT_ATTR(2, 3);
 
@@ -122,16 +108,12 @@ static inline char *realpath(const char *path, char *resolved_path)
 void configure_icount(const char *option);
 extern int use_icount;
 
-/* FIXME: Remove NEED_CPU_H.  */
-#ifndef NEED_CPU_H
-
 #include "qemu/osdep.h"
 #include "qemu/bswap.h"
 
-#else
-
+/* FIXME: Remove NEED_CPU_H.  */
+#ifdef NEED_CPU_H
 #include "cpu.h"
-
 #endif /* !defined(NEED_CPU_H) */
 
 /* main function, renamed */

include/qemu/osdep.h

@@ -1,6 +1,7 @@
 #ifndef QEMU_OSDEP_H
 #define QEMU_OSDEP_H
 
+#include "config-host.h"
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdbool.h>
@@ -161,6 +162,22 @@ int qemu_close(int fd);
 int qemu_create_pidfile(const char *filename);
 int qemu_get_thread_id(void);
 
+#ifndef CONFIG_IOVEC
+struct iovec {
+    void *iov_base;
+    size_t iov_len;
+};
+/*
+ * Use the same value as Linux for now.
+ */
+#define IOV_MAX 1024
+
+ssize_t readv(int fd, const struct iovec *iov, int iov_cnt);
+ssize_t writev(int fd, const struct iovec *iov, int iov_cnt);
+#else
+#include <sys/uio.h>
+#endif
+
 #ifdef _WIN32
 static inline void qemu_timersub(const struct timeval *val1,
                                  const struct timeval *val2,

util/iov.c

@@ -99,7 +99,7 @@ size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt)
 static ssize_t
 do_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, bool do_send)
 {
-#if defined CONFIG_IOVEC && defined CONFIG_POSIX
+#ifdef CONFIG_POSIX
     ssize_t ret;
     struct msghdr msg;
     memset(&msg, 0, sizeof(msg));

util/osdep.c

@@ -429,3 +429,46 @@ int socket_init(void)
 #endif
     return 0;
 }
+
+#ifndef CONFIG_IOVEC
+/* helper function for iov_send_recv() */
+static ssize_t
+readv_writev(int fd, const struct iovec *iov, int iov_cnt, bool do_write)
+{
+    unsigned i = 0;
+    ssize_t ret = 0;
+    while (i < iov_cnt) {
+        ssize_t r = do_write
+            ? write(fd, iov[i].iov_base, iov[i].iov_len)
+            : read(fd, iov[i].iov_base, iov[i].iov_len);
+        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) {
+                ret = -1;
+            }
+            break;
+        }
+        i++;
+    }
+    return ret;
+}
+
+ssize_t
+readv(int fd, const struct iovec *iov, int iov_cnt)
+{
+    return readv_writev(fd, iov, iov_cnt, false);
+}
+
+ssize_t
+writev(int fd, const struct iovec *iov, int iov_cnt)
+{
+    return readv_writev(fd, iov, iov_cnt, true);
+}
+#endif