Re: [ECOS] non blocking serial read returns EAGAIN

[Jonathan Larmour <jlarmour at redhat dot com>]

Phung Te Ha wrote:
> 
> Hi everyone,
> 
> Would like to have your idea on the following:
> 
>         . cyg_io_read on a serial port, previously set to non
> blocking returns EAGAIN if less than buffer's len has
> been read.
> 
>         . This  breaks the following situation:
>         1. set to non blocking the serial port
>         2. call select on the port, wait for data.
>         3. on return of select, call read to take the data
> out.
>         4. let's say there's less data than buffer's len, the
> dev_fo_read returns error even before setting read len
> to the uio, and read returns -1, always, even when
> data has been read...
> 
> My question is:
>         . why would cyg_io_read return error in this case?

It's a different interface with different semantics. It returns -EAGAIN if
less data was returned than expected. Instead it should be the code in
dev_fo_read (and dev_fo_write) that tests for this. Something like just:

Index: devfs.cxx
===================================================================
RCS file: /home/cvs/ecc/ecc/io/fileio/current/src/devfs.cxx,v
retrieving revision 1.4
diff -u -5 -p -r1.4 devfs.cxx
--- devfs.cxx	2000/08/01 08:59:43	1.4
+++ devfs.cxx	2001/07/19 18:58:59
@@ -335,10 +335,15 @@ static int dev_fo_read      (struct CYG_
     
         err = cyg_io_read( (cyg_io_handle_t)fp->f_data,
                            iov->iov_base,
                            &len);
 
+        if( EAGAIN == err ) // must be in non-blocking mode
+        {
+            uio->uio_resid -= len;
+            return ENOERR;
+        }
         if( err < 0 ) break;
 
         uio->uio_resid -= len;
     }
     
@@ -361,10 +366,15 @@ static int dev_fo_write     (struct CYG_
     
         err = cyg_io_write( (cyg_io_handle_t)fp->f_data,
                             iov->iov_base,
                             &len);
 
+        if( EAGAIN == err ) // must be in non-blocking mode
+        {
+            uio->uio_resid -= len;
+            return ENOERR;
+        }
         if( err < 0 ) break;
 
         uio->uio_resid -= len;
     }
 


Jifl
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