[sane-devel] Microtek SANE bug and fix for ADF

[Maurice Hilarius]

If you have a Microtek or similar scanner with an automatic document feeder 
(ADF) then there is a bug in the SANE code for using this feeder device.

We have been working with a Microtek ScanMaker X12USL, and ran into a 
problem with the code for the ADF handling.
After a multi-page scan, it would crash you right out of X!

As this is not a desirable feature, we have been looking into the reasons 
for this.

Fortunately we have found it, and I include a patch at the end of this message.

The problem is in the 'cancel_scan()' function in microtek2.c.

When using the automatic document feeder, after it has scanned all the 
pages, and there are no more pages to scan, this function is called after 
an I/O error ir produced by the lack of a page to feed.
It is then supposed to stop the scanner from trying to scan any more pages.

A comment in the code says:

"/* READ IMAGE with a transferlength of 0 aborts a scan */".

This is fine, but then 'close(ms->fd[1])'  may be called
ms->fd[1] equal to -1      (which does not have any nasty consequences,)

BUT! a bit below that you effectively have 'kill(-1, SIGTERM);'.

Try 'man 2 kill' to see what this does. :-)

After this patch:

--- sane-backends-1.0.5/backend/microtek2.c~	Sun May 27 04:20:20 2001
+++ sane-backends-1.0.5/backend/microtek2.c	Mon Nov 19 19:11:05 2001
@@ -1403,8 +1403,15 @@
          status = SANE_STATUS_CANCELLED;

      close(ms->fd[1]);
-    kill(ms->pid, SIGTERM);
-    waitpid(ms->pid, NULL, 0);
+    /* if we are aborting a scan because, for example, we run out
+       of material on a feeder, then pid may be already -1 and
+       kill(-1, SIGTERM), i.e. killing all our processes, is not
+       likely what we really want - --mj, 2001/Nov/19 */
+    if (ms->pid > 1)
+      {
+	kill(ms->pid, SIGTERM);
+	waitpid(ms->pid, NULL, 0);
+      }

      return status;
  }

With this revision of the code runs of batch scans using "ADF" settings 
terminate properly and without any other visible side-effects.

I have no idea if other backends have similar problems; 'kill()' call
is used in a number of places.


Meanwhile, an other trivial trouble we see is that 'scanimage' without any 
explicitly specified format is still using an extension of '.pnm' even if 
'--format tiff' is given.

For further excitement the manpage claims that "out%d.tif" is _always_ the 
default; at least in the presence of '--batch'.

Perhaps this is related to the "features" of a given scanner,  but with the 
"ScanMaker X12USL", (while using the microtek2 backend), we are getting 
"stripes" on both sides of scanned images.

'--backend-calibration' options, which some docs suggest may help with 
that, is listed by 'scanimage --help' as "[inactive]".

Indeed, it seems to not make any difference.

Does anyone have any suggestions or ideas for what to do with that problem?

Maurice Hilarius and  Michal Jaegermann

maurice@harddata.com
michal@harddata.com


With our best regards,

Maurice W. Hilarius       Telephone: 01-780-456-9771
Hard Data Ltd.               FAX:       01-780-456-9772
11060 - 166 Avenue        mailto:maurice@harddata.com
Edmonton, AB, Canada      http://www.harddata.com/
    T5X 1Y3