ALSA: ctl: Fix copy of updated id with element read/write
When control_compat.c:copy_ctl_value_to_user() is used, by ctl_elem_read_user() & ctl_elem_write_user(), it must also copy back the snd_ctl_elem_id value that may have been updated (filled in) by the call to snd_ctl_elem_read/snd_ctl_elem_write(). This matches the functionality provided by snd_ctl_elem_read_user() and snd_ctl_elem_write_user(), via snd_ctl_build_ioff(). Without this, and without making additional calls to snd_ctl_info() which are unnecessary when using the non-compat calls, a userspace application will not know the numid value for the element and consequently will not be able to use the poll/read interface on the control file to determine which elements have updates. Signed-off-by:Alan Young <consult.awy@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20211202150607.543389-1-consult.awy@gmail.com Signed-off-by:
Takashi Iwai <tiwai@suse.de>
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6665bb30