snd_pcm_sgbuf_ops_page 1246 include/sound/pcm.h #define snd_pcm_sgbuf_ops_page	NULL
snd_pcm_sgbuf_ops_page  264 sound/core/pcm_memory.c struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, unsigned long offset)