dynamic_debug in kernel

kernel 裡面有很多 pr_debug，這是被合 dynamic_debug 這個功能的 printk function。
在 Documentation/dynamic-debug-howto.txt 有說明。

大概就是：

1. menuconfig 圈選 dynamic_debugCONFIG_DYNAMIC_DEBUG=y
2. 系統啟動後，手動 mount debugfs : #mkdir /mnt/debugfs #mount -t debugfs none /mnt/debugfs
3. 把 /mnt/debugfs/dynamic_debug/control 打開來看..
4. control 會列出所有 pr_debug 所在的source file 和位置，用 echo ... 可以把該 pr_debug 打開或關閉

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control 檔的內容大概是: ... drivers/i2c/busses/mxc_i2c_hs.c:154 [mxc_i2c_hs]mxci2c_hs_bus_busy - "%s: Bus Busy!\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:264 [mxc_v4l2_capture]mxc_free_frames - "In MVC:mxc_free_frames\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:413 [mxc_v4l2_capture]mxc_streamoff - "In MVC:mxc_streamoff\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2825 [mxc_v4l2_capture]camera_init - "In MVC:camera_init\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:574 [mxc_v4l2_capture]start_preview - "MVC: start_preview\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:592 [mxc_v4l2_capture]start_preview - "End of %s: v2f pix widthxheight %d x %d\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:595 [mxc_v4l2_capture]start_preview - "End of %s: crop_bounds widthxheight %d x %d\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:598 [mxc_v4l2_capture]start_preview - "End of %s: crop_defrect widthxheight %d x %d\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:601 [mxc_v4l2_capture]start_preview - "End of %s: crop_current widthxheight %d x %d\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:617 [mxc_v4l2_capture]stop_preview - "MVC: stop preview\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:335 [mxc_v4l2_capture]mxc_streamon - "In MVC:mxc_streamon\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2714 [mxc_v4l2_capture]mxc_v4l2_resume p "In MVC:mxc_v4l2_resume\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2681 [mxc_v4l2_capture]mxc_v4l2_suspend - "In MVC:mxc_v4l2_suspend\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2812 [mxc_v4l2_capture]mxc_v4l2_master_detach - "In MVC:mxc_v4l2_master_detach\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2756 [mxc_v4l2_capture]mxc_v4l2_master_attach - "In MVC: mxc_v4l2_master_attach\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2757 [mxc_v4l2_capture]mxc_v4l2_master_attach - " slave.name = %s\012" drivers/media/video/mxc/capture/mxc_v4l2_capture.c:2758 [mxc_v4l2_capture]mxc_v4l2_master_attach - " master.name = %s\012" .. 中間那個 "-" 就代表不印出來，
若是 "p" 就代表要印出來。

所以要是希望 mxc_v4l2_capture.c 裡所有的 pr_debug 都印出來，可以用： echo 'file mxc_v4l2_capture.c +p' > control 如果不要了，就用： echo 'file mxc_v4l2_capture.c -p' > control 如果只是要第 617 行的 stop preview 印出來，就用： echo 'file mxc_v4l2_capture.c line 617 +p' > control

1. 雖然是enable print，但是 print level 還是follow 當初source code 寫得，所以有些還是要用 dmesg 才會看得到。
2. 可以對 control 使用grep command，不必每次都cat 出來