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Subject:	No errno set after too many open("/dev/ptmx", ...)
To:	cygwin AT cygwin DOT com
Message-ID:	<48de5cb5-5150-9f88-d744-2ab66a561b1e@t-online.de>
Date:	Sun, 30 Mar 2025 15:01:36 +0200
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From:	Christian Franke via Cygwin <cygwin AT cygwin DOT com>
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Found because 'stress-ng --pty 1' reports "open /dev/ptmx failed, errno=0":

$ uname -r # also with 3.5.7-1 and 3.6.0-1.x86_64
3.7.0-0.19.g6c5537c0298e.x86_64

$ cat manyptmx.c
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

int main()
{
   int fd;
   errno = __ELASTERROR;
   do {
     fd = open("/dev/ptmx", O_RDWR);
     printf("%d, %d\n", fd, errno);
   } while (fd >= 0);
   return 0;
}

$ gcc -o manyptmx manyptmx.c

$ ./manyptmx
3, 2000
4, 2000
...
127, 2000
128, 2000
       0 [main] manyptmx 204 tty_list::allocate: No pty allocated
                                                       -1, 2000

-- 
Regards,
Christian


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