We have an ioctl to inform the PCM protocol version the running kernel supports, but there is no way to know which protocol version the user-space can understand. This lack of information caused headaches in the past when we tried to extend the ABI. For example, because we couldn't guarantee the validity of the reserved bytes, we had to introduce a new ioctl SNDRV_PCM_IOCTL_STATUS_EXT for assigning a few new fields in the formerly reserved bits. If we could know that it's a new alsa-lib, we could assume the availability of the new fields, thus we could have reused the existing SNDRV_PCM_IOCTL_STATUS. In order to improve the ABI extensibility, this patch adds a new ioctl for user-space to inform its supporting protocol version to the kernel. By reporting the supported protocol from user-space, the kernel can judge which feature should be provided and which not. With the addition of the new ioctl, the PCM protocol version is bumped to 2.0.14, too. User-space checks the kernel protocol version via SNDRV_PCM_INFO_PVERSION, then it sets the supported version back via SNDRV_PCM_INFO_USER_PVERSION.
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| @@ -152,7 +152,7 @@ struct snd_hwdep_dsp_image { · 151 unmodified lines | |||
| 152 | * * | 152 | * * |
| 153 | *****************************************************************************/ | 153 | *****************************************************************************/ |
| 154 | 154 | ||
| 155 | #define SNDRV_PCM_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 13) | 155 | #define SNDRV_PCM_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 14) |
| 156 | 156 | ||
| 157 | typedef unsigned long snd_pcm_uframes_t; | 157 | typedef unsigned long snd_pcm_uframes_t; |
| 158 | typedef signed long snd_pcm_sframes_t; | 158 | typedef signed long snd_pcm_sframes_t; |
| @@ -564,6 +564,7 @@ enum { · 405 unmodified lines | |||
| 564 | #define SNDRV_PCM_IOCTL_INFO _IOR('A', 0x01, struct snd_pcm_info) | 564 | #define SNDRV_PCM_IOCTL_INFO _IOR('A', 0x01, struct snd_pcm_info) |
| 565 | #define SNDRV_PCM_IOCTL_TSTAMP _IOW('A', 0x02, int) | 565 | #define SNDRV_PCM_IOCTL_TSTAMP _IOW('A', 0x02, int) |
| 566 | #define SNDRV_PCM_IOCTL_TTSTAMP _IOW('A', 0x03, int) | 566 | #define SNDRV_PCM_IOCTL_TTSTAMP _IOW('A', 0x03, int) |
| 567 | #define SNDRV_PCM_IOCTL_USER_PVERSION _IOW('A', 0x04, int) | ||
| 567 | #define SNDRV_PCM_IOCTL_HW_REFINE _IOWR('A', 0x10, struct snd_pcm_hw_params) | 568 | #define SNDRV_PCM_IOCTL_HW_REFINE _IOWR('A', 0x10, struct snd_pcm_hw_params) |
| 568 | #define SNDRV_PCM_IOCTL_HW_PARAMS _IOWR('A', 0x11, struct snd_pcm_hw_params) | 569 | #define SNDRV_PCM_IOCTL_HW_PARAMS _IOWR('A', 0x11, struct snd_pcm_hw_params) |
| 569 | #define SNDRV_PCM_IOCTL_HW_FREE _IO('A', 0x12) | 570 | #define SNDRV_PCM_IOCTL_HW_FREE _IO('A', 0x12) |