compat_ioctl: unknown cmd on serial /dev/console

[Atsushi Nemoto]

After the commit fb07a5f8 ("compat_ioctl: remove all VT ioctl
handling"), I got this error message on 64-bit mips kernel with 32-bit
busybox userland:

ioctl32(init:1): Unknown cmd fd(0) cmd(00005600){t:'V';sz:0} arg(7fd76480) on /dev/console

The cmd 5600 is VT_OPENQRY.  The busybox's init issues this ioctl to
know vt-console or serial-console.  If the console was serial console,
VT ioctls are not handled by the serial driver.

How this error should be fixed?  Is this patch OK?

diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index 332dd00..731478f 100644
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -1005,6 +1005,8 @@ COMPATIBLE_IOCTL(SCSI_IOCTL_SEND_COMMAND)
 COMPATIBLE_IOCTL(SCSI_IOCTL_PROBE_HOST)
 COMPATIBLE_IOCTL(SCSI_IOCTL_GET_PCI)
 #endif
+/* Big V (for serial console case) */
+COMPATIBLE_IOCTL(VT_OPENQRY)
 /* Little p (/dev/rtc, /dev/envctrl, etc.) */
 COMPATIBLE_IOCTL(RTC_AIE_ON)
 COMPATIBLE_IOCTL(RTC_AIE_OFF)

And by quick search, I found some programs using VT_GETMODE to check
vt-console is available or not.  So VT_GETMODE might be an another
candidate, but not sure.

---
Atsushi Nemoto
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