[Xcb] [PATCH] Allow xcb_send_request with >UIO_MAXIOV iovecs

[Peter Harris]

This allows an application to do a scatter/gather operation on a large
image buffer to avoid the extra memcpy.

MacOSX 10.6 mentions UIO_MAXIOV in the man page for writev, but does not
define it in any header. Use autoconf to test for MAX_IOV from
<limits.h> in that case.

Signed-off-by: Peter Harris <pharris at opentext.com>
---

Unfortunately, AC_USE_SYSTEM_EXTENSIONS didn't work on Debian. Could you
please try this version and let me know what it does for you?

 configure.ac   |    7 +++++++
 src/xcb_conn.c |    7 ++++++-
 2 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/configure.ac b/configure.ac
index e94e32c..4e9eab2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -110,6 +110,13 @@ dnl check for support for Solaris Trusted Extensions
 AC_CHECK_HEADERS([tsol/label.h])
 AC_CHECK_FUNCS([is_system_labeled])
 
+dnl check for UIO_MAXIOV, or at least IOV_MAX
+AC_CHECK_DECL([UIO_MAXIOV], [],
+	      [AC_CHECK_DECL([IOV_MAX], [AC_DEFINE([UIO_MAXIOV], [IOV_MAX])],
+					[AC_DEFINE([UIO_MAXIOV], [16], [Define if not provided by <sys/uio.h>])],
+					[[#include <limits.h>]])],
+	      [[#include <sys/uio.h>]])
+
 xcbincludedir='${includedir}/xcb'
 AC_SUBST(xcbincludedir)
 
diff --git a/src/xcb_conn.c b/src/xcb_conn.c
index 725502a..9abd640 100644
--- a/src/xcb_conn.c
+++ b/src/xcb_conn.c
@@ -32,6 +32,7 @@
 #include <stdlib.h>
 #include <fcntl.h>
 #include <errno.h>
+#include <limits.h>
 
 #include "xcb.h"
 #include "xcbint.h"
@@ -204,7 +205,11 @@ static int write_vec(xcb_connection_t *c, struct iovec **vector, int *count)
          i++;
     }
 #else
-    n = writev(c->fd, *vector, *count);
+    n = *count;
+    if (n > UIO_MAXIOV)
+	n = UIO_MAXIOV;
+
+    n = writev(c->fd, *vector, n);
     if(n < 0 && errno == EAGAIN)
         return 1;
 #endif /* _WIN32 */    
-- 
1.7.2.5