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This new ioctl only returns the status byte (STB) that was originally sent by the device due to a service request (SRQ) condition. This ioctl checks the srq_asserted bit of the associated file descriptor. If set, the srq_asserted bit is reset and the cached STB with original SRQ information is returned. Otherwise the ioctl returns the error code ENOMSG. This ioctl is useful to support non USBTMC-488 compliant devices. Time sensitive applications can read the cached STB without incurring the cost of an urb transaction over the bus. Tested-by: Jian-Wei Wu <jian-wei_wu@keysight.com> Reviewed-by: Guido Kiener <guido.kiener@rohde-schwarz.com> Signed-off-by: Dave Penkler <dpenkler@gmail.com> Link: https://lore.kernel.org/r/20201215155621.9592-4-dpenkler@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>