+
+struct pipe {
+ struct charbuf data;
+ size_t bufmax;
+ int closed;
+ struct muth *r, *w;
+};
+
+static void freepipe(struct pipe *p)
+{
+ buffree(p->data);
+ free(p);
+}
+
+static ssize_t piperead(void *pdata, void *buf, size_t len)
+{
+ struct pipe *p = pdata;
+ ssize_t ret;
+
+ while(p->data.d == 0) {
+ if(p->closed & 2)
+ return(0);
+ if(p->r) {
+ errno = EBUSY;
+ return(-1);
+ }
+ p->r = current;
+ yield();
+ p->r = NULL;
+ }
+ ret = min(len, p->data.d);
+ memcpy(buf, p->data.b, ret);
+ memmove(p->data.b, p->data.b + ret, p->data.d -= ret);
+ if(p->w)
+ resume(p->w, 0);
+ return(ret);
+}
+
+static int piperclose(void *pdata)
+{
+ struct pipe *p = pdata;
+
+ if(p->closed & 2) {
+ freepipe(p);
+ } else {
+ p->closed |= 1;
+ if(p->w)
+ resume(p->w, 0);
+ }
+ return(0);
+}
+
+static ssize_t pipewrite(void *pdata, const void *buf, size_t len)
+{
+ struct pipe *p = pdata;
+ ssize_t ret;
+
+ if(p->closed & 1) {
+ errno = EPIPE;
+ return(-1);
+ }
+ while(p->data.d >= p->bufmax) {
+ if(p->w) {
+ errno = EBUSY;
+ return(-1);
+ }
+ p->w = current;
+ yield();
+ p->w = NULL;
+ if(p->closed & 1) {
+ errno = EPIPE;
+ return(-1);
+ }
+ }
+ ret = min(len, p->bufmax - p->data.d);
+ sizebuf(p->data, p->data.d + ret);
+ memcpy(p->data.b + p->data.d, buf, ret);
+ p->data.d += ret;
+ if(p->r)
+ resume(p->r, 0);
+ return(ret);
+}
+
+static int pipewclose(void *pdata)
+{
+ struct pipe *p = pdata;
+
+ if(p->closed & 1) {
+ freepipe(p);
+ } else {
+ p->closed |= 2;
+ if(p->r)
+ resume(p->r, 0);
+ }
+ return(0);
+}
+
+void mtiopipe(FILE **read, FILE **write)
+{
+ struct pipe *p;
+
+ omalloc(p);
+ p->bufmax = 4096;
+ *read = funstdio(p, piperead, NULL, NULL, piperclose);
+ *write = funstdio(p, NULL, pipewrite, NULL, pipewclose);
+}