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Date: Wed, 20 Aug 2008 19:06:55 +0200
From: Philippe Gerum <rpm@xenomai.org>
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Subject: Re: [Xenomai-help] uClinux write to pipe returning -ENOMEM
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To: Filip Van Rillaer <Filip.VanRillaer@domain.hid>
Cc: xenomai@xenomai.org

Filip Van Rillaer wrote:
> Hello,
> 
> Thank you for your work-around.
> Though I have some problems with the implementation:
> pipe_i_handler (Xenomai side) does not know when the xnpipe_write got
> errno=ENOMEM (the pipe_i_handler is I think even not called in case
> ENOMEM is returned).  So there is I think with the current Xenomai
> implementation no way for the pipe_i_handler to correctly fill in the
> value of buffer_filled_up_p.  This would mean that my writer-thread
> 'userland' would have to set this 'variable'.
> Then I was thinking about moving the <<rt_sem_p(&bsync, TM_INFINITE)>>
> to the writer-thread when errno-ENOMEM is returned, but that would
> require that the writer-thread has to bind the semaphore that was
> created in another program.  This is probably possible via the Xenomai
> registry.
>

This patch should be better. We need to retry allocating the buffer once the
monitoring handler has returned with success (i.e. returning 0 causes the retry).

--- include/native/pipe.h	(revision 4105)
+++ include/native/pipe.h	(working copy)
@@ -35,6 +35,7 @@
 #define P_EVENT_INPUT	1
 #define P_EVENT_OUTPUT	2
 #define P_EVENT_CLOSE	3
+#define P_EVENT_FULL	4

 typedef struct rt_pipe_placeholder {
     xnhandle_t opaque;
Index: ksrc/skins/native/pipe.c
===================================================================
--- ksrc/skins/native/pipe.c	(revision 4105)
+++ ksrc/skins/native/pipe.c	(working copy)
@@ -89,9 +89,15 @@
 static void *__pipe_alloc_handler(int bminor, size_t size, void *cookie)
 {
 	RT_PIPE *pipe = (RT_PIPE *)cookie;
+	void *buf;

 	/* Allocate memory for the incoming message. */
-	return xnheap_alloc(pipe->bufpool, size);
+	buf = xnheap_alloc(pipe->bufpool, size);
+	if (buf == NULL && pipe->monitor != NULL &&
+	    pipe->monitor(pipe, P_EVENT_FULL) == 0)
+		buf = xnheap_alloc(pipe->bufpool, size);
+
+	return buf;
 }

 static int __pipe_output_handler(int bminor,

-- 
Philippe.