[ECOS] non blocking serial read returns EAGAIN

[ECOS] non blocking serial read returns EAGAIN

[Phung Te Ha]

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?

Thanks for your idea.

Phungte

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Re: [ECOS] non blocking serial read returns EAGAIN

[Jonathan Larmour]

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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