ALSA: Avoid using timespec for struct snd_pcm_status

The struct snd_pcm_status will use 'timespec' type variables to record
timestamp, which is not year 2038 safe on 32bits system.

Userspace will use SNDRV_PCM_IOCTL_STATUS and SNDRV_PCM_IOCTL_STATUS_EXT
as commands to issue ioctl() to fill the 'snd_pcm_status' structure in
userspace. The command number is always defined through _IOR/_IOW/IORW,
so when userspace changes the definition of 'struct timespec' to use
64-bit types, the command number also changes.

Thus in the kernel, we now need to define two versions of each such ioctl
and corresponding ioctl commands to handle 32bit time_t and 64bit time_t
in native mode:
struct snd_pcm_status32 {
	......

	s32 trigger_tstamp_sec;
	s32 trigger_tstamp_nsec;

	......

	s32 audio_tstamp_sec;
	s32 audio_tstamp_nsec;

	......
};

struct snd_pcm_status64 {
	......

	s32 trigger_tstamp_sec;
	s32 trigger_tstamp_nsec;

	......

	s32 audio_tstamp_sec;
	s32 audio_tstamp_nsec;

	......
};

Moreover in compat file, we renamed or introduced new structures to handle
32bit/64bit time_t in compatible mode. The 'struct snd_pcm_status32' and
snd_pcm_status_user32() are used to handle 32bit time_t in compat mode.
'struct compat_snd_pcm_status64' and snd_pcm_status_user_compat64() are used
to handle 64bit time_t.

The implicit padding before timespec is made explicit to avoid incompatible
structure layout between 32-bit and 64-bit x86 due to the different
alignment requirements, and the snd_pcm_status structure is now hidden
from the kernel to avoid relying on the timespec definitio definitionn

Finally we can replace SNDRV_PCM_IOCTL_STATUS and SNDRV_PCM_IOCTL_STATUS_EXT
with new commands and introduce new functions to fill new 'struct snd_pcm_status64'
instead of using unsafe 'struct snd_pcm_status'. Then in future, the new
commands can be matched when userspace changes 'timespec' to 64bit type
to make a size change of 'struct snd_pcm_status'. When glibc changes time_t
to 64-bit, any recompiled program will issue ioctl commands that the kernel
does not understand without this patch.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 40a23d8418fe..d2c88c098b20 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -456,8 +456,13 @@ enum {
 	SNDRV_PCM_AUDIO_TSTAMP_TYPE_LAST = SNDRV_PCM_AUDIO_TSTAMP_TYPE_LINK_SYNCHRONIZED
 };
 
+#ifndef __KERNEL__
+/* explicit padding avoids incompatibility between i386 and x86-64 */
+typedef struct { unsigned char pad[sizeof(time_t) - sizeof(int)] __time_pad;
+
 struct snd_pcm_status {
 	snd_pcm_state_t state;		/* stream state */
+	__time_pad pad1;		/* align to timespec */
 	struct timespec trigger_tstamp;	/* time when stream was started/stopped/paused */
 	struct timespec tstamp;		/* reference timestamp */
 	snd_pcm_uframes_t appl_ptr;	/* appl ptr */
@@ -473,6 +478,7 @@ struct snd_pcm_status {
 	__u32 audio_tstamp_accuracy;	/* in ns units, only valid if indicated in audio_tstamp_data */
 	unsigned char reserved[52-2*sizeof(struct timespec)]; /* must be filled with zero */
 };
+#endif
 
 struct snd_pcm_mmap_status {
 	snd_pcm_state_t state;		/* RO: state - SNDRV_PCM_STATE_XXXX */