[ECOS] nonblocking read call (dev_fo_read)

[ECOS] nonblocking read call (dev_fo_read)

[Roland Caßebohm]

Hi,

I have a problem using the serial device nonblocking.

I have enabled CYGOPT_IO_SERIAL_SUPPORT_NONBLOCKING.
In my application I use:

   fd=open("/dev/ser0", O_RDWR | O_NONBLOCK);

If I do a read call:

   received=read(fd,buf,10);
   if (received<0)
      perror("read");
	
I get the error "Try again later", although the read call had get data. With 
debugging I think I have found what is wrong. The serial device driver 
function returns allways with -EAGAIN, if there is data or not. In the 
function "dev_fo_read" will be compared if err is EAGAIN. Here is it going 
wrong, because err is -EAGAIN not EAGAIN.

In "dev_fo_read":

   if( EAGAIN == err ) // must be in non-blocking mode
   {
        uio->uio_resid -= len;
        return ENOERR;
   }

I think this must be:

   if( EAGAIN == -err ) // must be in non-blocking mode
   {
        uio->uio_resid -= len;
        return ENOERR;
   }
 
Does anybody know if this is the right change to make this work?

Thanks,

Roland

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Re: [ECOS] nonblocking read call (dev_fo_read)

[Nick Garnett]

Roland Caßebohm <roland.cassebohm@visionsystems.de> writes:

> Does anybody know if this is the right change to make this work?
> 

Yep, that looks like a bug. It also needs changing in
dev_fo_write(). I've applied the following patch to our repository:


Index: ChangeLog
===================================================================
RCS file: /home/cvs/ecc/ecc/io/fileio/current/ChangeLog,v
retrieving revision 1.45
diff -u -5 -r1.45 ChangeLog
--- ChangeLog	2002/03/07 16:19:27	1.45
+++ ChangeLog	2002/04/05 12:17:43
@@ -1,5 +1,10 @@
+2002-04-05  Nick Garnett  <nickg@redhat.com>
+
+	* src/devfs.cxx: Changed test for EAGAIN in dev_fo_read() and
+	dev_fo_write() to negate value first. 
+
 2002-03-07  Nick Garnett  <nickg@redhat.com>
 
 	* doc/fileio.sgml: Added this file to contain documentation on
 	this package.
 
Index: src/devfs.cxx
===================================================================
RCS file: /home/cvs/ecc/ecc/io/fileio/current/src/devfs.cxx,v
retrieving revision 1.7
diff -u -5 -r1.7 devfs.cxx
--- src/devfs.cxx	2002/01/23 15:35:13	1.7
+++ src/devfs.cxx	2002/04/05 12:17:43
@@ -341,11 +341,11 @@
         else
             err = cyg_io_read( (cyg_io_handle_t)t,
                                iov->iov_base,
                                &len);
 
-        if( EAGAIN == err ) // must be in non-blocking mode
+        if( -EAGAIN == err ) // must be in non-blocking mode
         {
             uio->uio_resid -= len;
             return ENOERR;
         }
         if( err < 0 ) break;
@@ -378,11 +378,11 @@
         else
             err = cyg_io_write( (cyg_io_handle_t)t,
                                 iov->iov_base,
                                 &len);
 
-        if( EAGAIN == err ) // must be in non-blocking mode
+        if( -EAGAIN == err ) // must be in non-blocking mode
         {
             uio->uio_resid -= len;
             return ENOERR;
         }
         if( err < 0 ) break;



-- 
Nick Garnett, eCos Kernel Architect
Red Hat, Cambridge, UK


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