From 5b8cb7299a9e60f7bfeb3fe5f3d7556e2357d485 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Mon, 15 Jun 2009 13:31:41 +0100
Subject: [PATCH] WIP MIT-SHM; can create shm segment

---
 pctb/pages.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/pctb/pages.c b/pctb/pages.c
index ab3a2b0..1fba5a6 100644
--- a/pctb/pages.c
+++ b/pctb/pages.c
@@ -37,6 +37,10 @@
 #include <X11/keysym.h>
 #include <X11/Xutil.h>
 
+#include <X11/extensions/XShm.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
 CanonImage *page_images[MAX_PAGES];
 int npages;
 
@@ -49,6 +53,9 @@ static struct timeval tv_startup;
 static unsigned wwidth, wheight;
 static int max_relevant_y= -1;
 
+static XImage *shmim;
+static XShmSegmentInfo shminfo;
+
 DEBUG_DEFINE_DEBUGF(pages)
 
 #define xassert(what)					\
@@ -307,6 +314,55 @@ static void raise_and_get_details(void) {
     fatal("YPP client window is implausibly small?");
 
   check_client_window_all_on_screen();
+
+  int shm= XShmQueryExtension(disp);
+  if (shm) {
+    xassert( shmim= XShmCreateImage(disp, attr.visual, attr.depth, ZPixmap,
+				    0,&shminfo, wwidth,wheight) );
+
+    sigset_t oldset, all;
+    sigfillset(&all);
+    sysassert(! sigprocmask(SIG_BLOCK,&all,&oldset) );
+
+    int pfd[2];
+    pid_t cleaner;
+    sysassert(! pipe(pfd) );
+    sysassert( (cleaner= fork()) != -1 );
+    if (!cleaner) {
+      sysassert(! close(pfd[1]) );
+      for (;;) {
+	int r= read(pfd[0], &shminfo.shmid, sizeof(shminfo.shmid));
+	if (!r) exit(0);
+	if (r==sizeof(shminfo.shmid)) break;
+	assert(r==-1 && errno==EINTR);
+      }
+      for (;;) {
+	char bc;
+	int r= read(pfd[0],&bc,1);
+	if (r>=0) break;
+	assert(r==-1 && errno==EINTR);
+      }
+      sysassert(! shmctl(shminfo.shmid,IPC_RMID,0) );
+      exit(0);
+    }
+    sysassert(! close(pfd[0]) );
+
+    sysassert(! sigprocmask(SIG_SETMASK,&oldset,0) );
+
+    assert(shmim->height == wheight);
+    sysassert( (shminfo.shmid=
+		shmget(IPC_PRIVATE, shmim->bytes_per_line * wheight,
+		       IPC_CREAT|0600)) >= 0 );
+
+    sysassert( write(pfd[1],&shminfo.shmid,sizeof(shminfo.shmid)) ==
+	       sizeof(shminfo.shmid) );
+    sysassert( shminfo.shmaddr= shmat(shminfo.shmid,0,0) );
+    shmim->data= shminfo.shmaddr;
+    shminfo.readOnly= False;
+    xassert( XShmAttach(disp,&shminfo) );
+
+    close(pfd[1]); /* causes IPC_RMID */
+  }
 }
 
 static void set_focus(void) {
-- 
2.30.2