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POC: write file from kernel-module correct this way?
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copied!<p>I try to copy/write pcm-bytes (from ALSA-buffer) from the kernel-space into a file within a kernel-module (LKM).</p> <p>The file got's written and the size looks ok for me, but because it's PCM-data I can't see if it's correct (raw audio data, not readable).</p> <p>My audio-players (MPlayer="Invalid seek to negative position ffffffffffffffff!", VLC, Foobar2000) fail to play my written file so I think I have a mistake in my code.</p> <p>When I open the file via SCITE I see many many "NUL" and other cryted stuff (bytes ;).</p> <p>Maybe one of you find a bug?</p> <p>I have this script:</p> <pre><code>unsigned char *dma_area; // this is the source, an mmapped-area int pcm_offset_bytes; // the actual offset in the dma_area int size_bytes; // the amount of bytes to copy struct file *target_file; // the target-file int ret; // used in write-process below int wrote = 0; // used in write-process below mm_segment_t fs; void *data; // dma_area + pcm_offset_bytes // (..) calculate offset and size // open the target file target_file = filp_open("/dev/snd/pcmC0D0p_output", (O_CREAT | O_TRUNC | O_WRONLY), (S_IRWXU | S_IRWXG | S_IRWXO)); data = dma_area + pcm_offset_bytes fs = get_fs(); set_fs (get_ds ()); if (!target_file || !target_file->f_op || !target_file->f_op->write) { LOGI("something's missing\n"); return -EIO; } // loop until every byte is written while (size_bytes > 0) { ret = target_file->f_op->write(target_file, (char *)data, size_bytes, &target_file->f_pos); LOGI ("wrote %d bytes to target_file@%p, return %d\n", size_bytes, target_file, ret); if (ret <= 0) goto done; size_bytes -= ret; data += ret; wrote += ret; } ret = wrote; done: set_fs(fs); LOGI("result %d\n", ret); </code></pre>

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