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.
Unified · Split
| @@ -218,6 +218,7 @@ struct snd_pcm_ops { · 217 unmodified lines | ||
| 218 | 218 | struct snd_pcm_file { |
| 219 | 219 | struct snd_pcm_substream *substream; |
| 220 | 220 | int no_compat_mmap; |
| 221 | + unsigned int user_pversion; /* supported protocol version */ | |
| 221 | 222 | }; |
| 222 | 223 | |
| 223 | 224 | struct snd_pcm_hw_rule; |
| @@ -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 | 157 | typedef unsigned long snd_pcm_uframes_t; |
| 158 | 158 | typedef signed long snd_pcm_sframes_t; |
| @@ -564,6 +564,7 @@ enum { · 405 unmodified lines | ||
| 564 | 564 | #define SNDRV_PCM_IOCTL_INFO _IOR('A', 0x01, struct snd_pcm_info) |
| 565 | 565 | #define SNDRV_PCM_IOCTL_TSTAMP _IOW('A', 0x02, int) |
| 566 | 566 | #define SNDRV_PCM_IOCTL_TTSTAMP _IOW('A', 0x03, int) |
| 567 | +#define SNDRV_PCM_IOCTL_USER_PVERSION _IOW('A', 0x04, int) | |
| 567 | 568 | #define SNDRV_PCM_IOCTL_HW_REFINE _IOWR('A', 0x10, struct snd_pcm_hw_params) |
| 568 | 569 | #define SNDRV_PCM_IOCTL_HW_PARAMS _IOWR('A', 0x11, struct snd_pcm_hw_params) |
| 569 | 570 | #define SNDRV_PCM_IOCTL_HW_FREE _IO('A', 0x12) |
| @@ -676,6 +676,7 @@ static long snd_pcm_ioctl_compat(struct file *file, unsigned int cmd, unsigned l · 675 unmodified lines | ||
| 676 | 676 | case SNDRV_PCM_IOCTL_INFO: |
| 677 | 677 | case SNDRV_PCM_IOCTL_TSTAMP: |
| 678 | 678 | case SNDRV_PCM_IOCTL_TTSTAMP: |
| 679 | + case SNDRV_PCM_IOCTL_USER_PVERSION: | |
| 679 | 680 | case SNDRV_PCM_IOCTL_HWSYNC: |
| 680 | 681 | case SNDRV_PCM_IOCTL_PREPARE: |
| 681 | 682 | case SNDRV_PCM_IOCTL_RESET: |
| @@ -2770,6 +2770,8 @@ static int snd_pcm_common_ioctl(struct file *file, · 2769 unmodified lines | ||
| 2770 | 2770 | struct snd_pcm_substream *substream, |
| 2771 | 2771 | unsigned int cmd, void __user *arg) |
| 2772 | 2772 | { |
| 2773 | + struct snd_pcm_file *pcm_file = file->private_data; | |
| 2774 | + | |
| 2773 | 2775 | switch (cmd) { |
| 2774 | 2776 | case SNDRV_PCM_IOCTL_PVERSION: |
| 2775 | 2777 | return put_user(SNDRV_PCM_VERSION, (int __user *)arg) ? -EFAULT : 0; |
| @@ -2779,6 +2781,11 @@ static int snd_pcm_common_ioctl(struct file *file, · 3 unmodified lines | ||
| 2779 | 2781 | return 0; |
| 2780 | 2782 | case SNDRV_PCM_IOCTL_TTSTAMP: |
| 2781 | 2783 | return snd_pcm_tstamp(substream, arg); |
| 2784 | + case SNDRV_PCM_IOCTL_USER_PVERSION: | |
| 2785 | + if (get_user(pcm_file->user_pversion, | |
| 2786 | + (unsigned int __user *)arg)) | |
| 2787 | + return -EFAULT; | |
| 2788 | + return 0; | |
| 2782 | 2789 | case SNDRV_PCM_IOCTL_HW_REFINE: |
| 2783 | 2790 | return snd_pcm_hw_refine_user(substream, arg); |
| 2784 | 2791 | case SNDRV_PCM_IOCTL_HW_PARAMS: |