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[Patch] linux: serial backend find too many ports #1562

michaelrsweet opened this issue Apr 14, 2006 · 2 comments


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commented Apr 14, 2006

Version: 1.2rc2 User: cryptic

When called without arguments, the serial backend on linux lists all potential serial ports instead of all present serial ports. Many of those ports do not correspond to actual hardware.

This happens because under Linux additional serial port hardware is setup using the device node. So this node needs to be present for any potential port, and serial finds it and lists it.

I fixed this by using an (Linux-specific) ioctl to check whether the serial port was setup, and to skip it if it is not. This only skips ports that are not usable. Ports that do not support the ioctl (i.e. are always setup/present) are listed as before.

Please (feel free to) apply!

Patch is against 1.2rc2


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commented Apr 14, 2006 User: mike

Fixed in Subversion repository.

I made the code conditional based on the TIOCGSERIAL definition.


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commented Apr 14, 2006


--- cups-1.2rc2/backend/serial.c 2006-03-07 23:07:44.000000000 +0100
+++ 2006-04-13 15:44:03.000000000 +0200
@@ -87,6 +87,10 @@

include <IOKit/IOBSD.h>

#endif /* APPLE */

+#if defined(linux) || defined(linux) || defined(__linux)
+# include <linux/serial.h>
+# include <linux/ioctl.h>


  • Local functions...
    @@ -670,13 +674,22 @@
    int i, j; /* Looping vars /
    int fd; /
    File descriptor */

    char device[255]; /* Device filename */

    • struct serial_struct serinfo; /* serial port info */

    for (i = 0; i < 100; i ++)
    sprintf(device, "/dev/ttyS%d", i);
    if ((fd = open(device, O_WRONLY | O_NOCTTY | O_NDELAY)) >= 0)

    •  serinfo.reserved_char[0] = 0; /\* setserial does this as well */
    •  if (ioctl(fd, TIOCGSERIAL, &serinfo)!=-1) /\* unsupported ioctl? */
    •  {
    • if (serinfo.type==PORT_UNKNOWN)
    • {
    • close(fd);
    • continue;
    • }
    •  }

      if defined(_ARCH_PPC) || defined(powerpc) || defined(__powerpc)

      printf("serial serial:%s?baud=230400 "Unknown" "Serial Port #%d"\n",
@michaelrsweet michaelrsweet added this to the Stable milestone Mar 17, 2016
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