4.8.22 gpm log spam / input misbehavior when using mc under screen via ssh without root privileges

[Bodo Eggert <7eggert online de>]

Please cc me on replies (reply to all)

If:
- I ssh to my server
- without root privileges
- then start a screen
- then start mc

Then:
- mc hammers gpm to open a connection
- gpm logs:
    Jan 16 14:49:13 nas10 /usr/sbin/gpm[2552]: *** warning
     [daemon/processconn.c(129)]: 
    Jan 16 14:49:13 nas10 /usr/sbin/gpm[2552]: Failed gpm connect attempt
     by uid 1000 for vc /dev/tty0
- mc logs:
    Jan 16 14:49:13 nas10 mc: *** info
    Jan 16 14:49:13 nas10 mc: Warning: closing connection
- mc will react to only each third keypress, no matter if it's a 
   normal character, ESC or a special key
- this causes high cpu usage in rsyslogd + itself
- similar but not same to https://midnight-commander.org/ticket/3208

Distribution: Devuan Beowulf
GNU Midnight Commander 4.8.22
Built with GLib 2.58.2
Using the S-Lang library with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm and Linux console
With support for X11 events
With internationalization support
With multiple codepages support
Virtual File Systems: cpiofs, tarfs, sfs, extfs, ext2undelfs, ftpfs, 
sftpfs, fish
Data types: char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

Home directory: /home/7eggert
Profile root directory: /home/7eggert

[System data]
    Config directory: /etc/mc/
    Data directory:   /usr/share/mc/
    File extension handlers: /usr/libexec/mc/ext.d/
    VFS plugins and scripts: /usr/libexec/mc/
        extfs.d:        /usr/libexec/mc/extfs.d/

[User data]
    Config directory: /home/7eggert/.config/mc/
    Data directory:   /home/7eggert/.local/share/mc/
        skins:          /home/7eggert/.local/share/mc/skins/
        extfs.d:        /home/7eggert/.local/share/mc/extfs.d/
        mcedit macros:  /home/7eggert/.local/share/mc/mc.macros
        mcedit external macros: 
/home/7eggert/.local/share/mc/mcedit/macros.d/macro.*
    Cache directory:  /home/7eggert/.cache/mc/

strace:

rt_sigaction(SIGTSTP, {sa_handler=SIG_IGN, sa_mask=[], 
sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, {sa_handler=SIG_DFL, 
sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, 8) = 0
rt_sigaction(SIGTSTP, {sa_handler=0x7fb0e3fd4990, sa_mask=[], 
sa_flags=SA_RESTORER|SA_NODEFER, sa_restorer=0x7fb0e3e13730}, NULL, 8) = 0
rt_sigaction(SIGINT, {sa_handler=0x55de15c7e690, sa_mask=[], 
sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, NULL, 8) = 0
select(10, [3 4 9], NULL, NULL, NULL)   = 1 (in [9])
rt_sigaction(SIGINT, {sa_handler=SIG_IGN, sa_mask=[], 
sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, NULL, 8) = 0
read(9, "", 28)                         = 0
sendto(10, "<14>Jan 16 15:18:09 mc: *** info"..., 33, MSG_NOSIGNAL, NULL, 
0) = 33
sendto(10, "<14>Jan 16 15:18:09 mc: Warning:"..., 51, MSG_NOSIGNAL, NULL, 
0) = 51
close(9)                                = 0
rt_sigaction(SIGTSTP, {sa_handler=SIG_DFL, sa_mask=[], 
sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, NULL, 8) = 0
rt_sigaction(SIGWINCH, {sa_handler=0x55de15c7d7f0, sa_mask=[], 
sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7fb0e3e13730}, NULL, 8) = 0
close(8)                                = 0
getpid()                                = 22829
ioctl(0, TCGETS, {B38400 -opost isig -icanon -echo ...}) = 0
ioctl(0, TCGETS, {B38400 -opost isig -icanon -echo ...}) = 0
fstat(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x7), ...}) = 0
readlink("/proc/self/fd/0", "/dev/pts/7", 4095) = 10
stat("/dev/pts/7", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x7), 
...}) = 0
openat(AT_FDCWD, "/dev/pts/7", O_WRONLY) = 8
ioctl(8, TIOCGWINSZ, {ws_row=81, ws_col=210, ws_xpixel=0, ws_ypixel=0}) = 
0
socket(AF_UNIX, SOCK_STREAM, 0)         = 9
connect(9, {sa_family=AF_UNIX, sun_path="/dev/gpmctl"}, 13) = 0
write(9, "\376\377\1\0\0\0\0\0-Y\0\0\0\0\0\0", 16) = 16
rt_sigaction(SIGWINCH, {sa_handler=0x7fb0e3fd3f50, sa_mask=[], 
sa_flags=SA_RESTORER, sa_restorer=0x7fb0e3e13730}, 
{sa_handler=0x55de15c7d7f0, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART, 
sa_restorer=0x7fb0e3e13730}, 8) = 0