As you can see in Documentation/ioctl/ioctl-number.txt
, the value 0x55 ('U'
) is used by several subsystems.
strace
does not know which of the several subsystem the device file belongs to, and might not recognize some newer ioctl codes.
The latest strace
version knows about SNDRV_CTL_IOCTL_PCM_NEXT_DEVICE
.