Experimental Physics and
Industrial Control System

Ron Sluiter <[email protected]> · Wed, 17 Apr 2013 17:19:10 -0500

Hello Vesna,

Two points...

1st, I checked this change into saveData.c

#ifdef vxWorks
    file= creat(tmpfile, 0640);
#else
    file= creat(tmpfile, O_RDWR);
#endif

on March 15, 2012.  We, here at APS, have been using that change
ever since, but it has not yet made it into an "official" sscan module
release (i.e, it is not available from the sscan web page). I think that
explains why you are having problems and we are not.

2nd, I believe Andrew's suggest is the better modification, i.e.,
replace the creat() call with,

    file = open(tmpfile, O_CREAT|O_RDWR|O_TRUNC, 0666);

As I understand it, the purpose of creating a file here is
verify R/W permissions. The above should be an OSI method
of doing that.

Ron

On 4/17/2013 10:36 AM, Tim Mooney wrote:

Hi Vesna,

If it were a bug in creat(), I'd expect the same behavior here with vxWorks
6.9, but Ron Sluiter verified that it works here.  Of course it may be that
your 6.9 is differently configured.  If so, saveData's sensitivity to the
difference might be good information to have, as more folks start using
vxWorks 6.x.

I'm concerned that there is something different about your system that might
have hard-to-diagnose consequences later, and I think we should turn over a
few more stones before just moving on.  I think open(..., O_CREAT, ...) is
not exactly the same as creat().  It would succeed if the file already
existed - perhaps because saveData lacks the ability to delete files - so it's
not a bulletproof indicator that saveData can create a new file.

Are you confident that you're using NFS?  vxWorks is pretty sneaky about
silently falling back to netDrv if an NFS mount to the path it needs is not
available.  But saveData is not tested with netDrv.  On vxWorks, saveData only
works reliably with NFS.

If you are using NFS, which version are you using?

Tim

----- Original Message -----

From: "Vesna Samardzic-Boban"<[email protected]>
To: "Tim Mooney"<[email protected]>, "Andrew Johnson"<[email protected]>
Cc:[email protected]
Sent: Wednesday, April 17, 2013 4:56:27 AM
Subject: RE: sscan/ saveData problem with RW permission, and not an NFS issue

Hi Tim and Andrew,

Agree with Andrew it is a vxWorks bug in creat().
But it's easier (for me) to replace the line/creat() in saveData.c
     file= creat(tmpfile, O_RDWR);
with open() e.g.
#ifdef vxWorks
     file = open (tmpfile, O_CREAT | O_RDWR, 0666);
#else
     file = creat (tmpfile, O_RDWR);       /* if this is needed by
     other OS's*/
#endif
That way we do not depend on Wind River and their bug/fix.

REgards Vesna

________________________________________
From: Andrew Johnson [[email protected]]
Sent: Wednesday, 17 April 2013 1:31 AM
To:[email protected]
Cc: Tim Mooney; Vesna Samardzic-Boban
Subject: Re: sscan/ saveData problem with RW permission, and not an
NFS issue

Hi Tim,

On 2013-04-16 Tim Mooney wrote:

Thanks for the information.  I haven't tested sscan on vxWorks 6.9,
though
I'm told it works on vxWorks 6.8.  I don't think creat() uses
O_RDRW as a
file-permission mask, and I don't understand why open() would work
while
creat() does not.  I'm ok with making this change, but I'd like to
understand it better first.

I don't think there's going to be any difference in the behavior
between
VxWorks 6.8 and 6.9.  This is one of those things that I believe Wind
River
got wrong very early in the life of VxWorks and it has never been
fixed
properly.  This is from the documentation for creat():
     The parameter mode is set to O_RDONLY (0), O_WRONLY (1), or
     O_RDWR (2)
     for the duration of time the file is open. On NFS and POSIX
     compliant
     file systems such as HRFS, mode refers instead to the UNIX style
     file
     permission bits.
They even say that the second argument has a different meaning on
different
file-systems, which means there is /no/ way to write code using this
routine
that works properly on all file-systems, because you have to know
what kind of
file-system it is to give the right parameter.
I recommend that creat() not be used in code that runs on vxWorks,
and that
all calls to it be replaced with the equivalent open() call instead.
  The
Linux man-page for creat() says:
     creat() is equivalent to open() with flags equal to
     O_CREAT|O_WRONLY|O_TRUNC.
You will also need to add the mode parameter 0666.
- Andrew
--
It is difficult to get a man to understand something, when his salary
depends upon his not understanding it. -- Upton Sinclair

________________________________________
From: Tim Mooney [[email protected]]
Sent: Wednesday, 17 April 2013 1:18 AM
To: Vesna Samardzic-Boban
Cc:[email protected]
Subject: Re: sscan/ saveData problem with RW permission, and not an
NFS issue

Hi Vesna,

Thanks for the information.  I haven't tested sscan on vxWorks 6.9,
though
I'm told it works on vxWorks 6.8.  I don't think creat() uses O_RDRW
as a
file-permission mask, and I don't understand why open() would work
while
creat() does not.  I'm ok with making this change, but I'd like to
understand
it better first.

Tim

----- Original Message -----

From: "Vesna Samardzic-Boban"
<[email protected]>
To:[email protected]
Sent: Monday, April 15, 2013 8:52:30 PM
Subject: sscan/ saveData problem with RW permission, and not an NFS
issue

Hi All,

Found a problem as follows:

Running a scan record on a vxWorks IOC and when entering 'File
system' in scan_saveData.adl screen, an error message in the 'Save
status' field follows:
"RW permission denied !!!"

At first I suspected NFS but after checking it found that my
problem
was in the sscan's saveData.c and/or VxWorks is 6.9

Tried two versions of sscan, 2-6-6 and 2-8-2, they gave the same
result as above. These two versions are same regarding the
saveData.c and its function
     checkRWpermission(char* path)
and specifically the line

     file= creat(tmpfile, O_RDWR);

that creates test file "rix_" with file permissions 002 (because
O_RDRW = 2)
(O_RDRW is flag "Open for reading and writing" or File Access
Options)

The file permissions 002 become
-------w-  in   terms of    rwxrwxrwx
and hence the error "RW permission denied !!!"

Found a solution by using vxWorks function open() instead of
creat().
open() - opens a file and optionally creates a file if it does not
exist.
open() - also offers a parameter for "mode" i.e. file permissions,
which i set to 0x666 in the example below

      file = open (tmpfile, O_CREAT | O_RDWR, 0666);

Then scan data can be saved as expected.

BTW
saveData.c uses open() for creating 'subdirectory'.
           fd = open (local_pathname, O_RDWR | O_CREAT,
                            FSTAT_DIR | DEFAULT_DIR_PERM | 0775);

Has anyone had similar problems ?
Is this an sscan/saveData.c issue or vxWorks 6.9 issue (I do not
have
any other version of vxWorks) ?
How about sscan/saveData on OS's other than vxWorks?

Thanks Vesna

P.S.
In my vxWorks 6.9 and its ioLib.c, creat() does not offer file
permissions (set to 0 as below):
int creat
     (
     const char *name,           /* name of the file to create */
     int         flag            /* file permissions */
     )
     {
     return (ioCreateOrOpen (name, flag, 0, TRUE));
     }

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System