Why dynamic debug in Linux does not show variable values?

Question

The outputs of dynamic debug for different drivers do not show any values. They instead show the formatting string values for expected data type. How can I fix it? Here is an extraction of file sys/kernel/debug/dynamic_debug/control for different drivers:

drivers/misc/mei/hw-me.c:994 [mei_me]mei_me_d0i3_exit_sync =_ "d0i3 exit ret = %d\012"
drivers/misc/mei/hw-me.c:970 [mei_me]mei_me_d0i3_exit_sync =_ "d0i3 exit wait not needed\012"
drivers/misc/mei/hw-me.c:963 [mei_me]mei_me_d0i3_exit_sync =_ "d0i3 exit not needed\012"
drivers/misc/mei/hw-me.c:940 [mei_me]mei_me_d0i3_enter =_ "d0i3 enter\012"
drivers/misc/mei/hw-me.c:932 [mei_me]mei_me_d0i3_enter =_ "already d0i3 : set not needed\012"
drivers/misc/mei/hw-me.c:910 [mei_me]mei_me_d0i3_enter_sync =_ "d0i3 enter ret = %d\012"
drivers/misc/mei/hw-me.c:887 [mei_me]mei_me_d0i3_enter_sync =_ "d0i3 enter wait not needed\012"
drivers/misc/mei/hw-me.c:859 [mei_me]mei_me_d0i3_enter_sync =_ "d0i3 set not needed\012"
drivers/misc/mei/hw-me.c:794 [mei_me]mei_me_pg_is_enabled =_ "pg: not supported: d0i3 = %d HGP = %d hbm version %d.%d ?= %d.%d\012"
drivers/misc/mei/hw-me.c:590 [mei_me]mei_me_count_full_read_slots =_ "filled_slots =%08x\012"
drivers/misc/mei/hw-me.c:541 [mei_me]mei_me_hbuf_write =_ "empty slots = %hu.\012"
drivers/misc/mei/hw-me.c:538 [mei_me]mei_me_hbuf_write =_ "hdr:host=%02d me=%02d len=%d internal=%1d comp=%1d"
drivers/misc/mei/hw-me.c:445 [mei_me]mei_me_hw_start =_ "hw is ready\012"
sound/core/init.c:116 [snd]init_info_for_card =_ "unable to create card entry\012"
sound/core/control.c:1537 [snd]snd_ctl_ioctl =_ "unknown ioctl = 0x%x\012"
sound/core/device.c:156 [snd]snd_device_free =_ "device free %p (from %pF), not found\012"
sound/core/device.c:132 [snd]snd_device_disconnect =_ "device disconnect %p (from %pF), not found\012"
sound/core/timer.c:262 [snd_timer]snd_timer_open =_ "ALSA: timer: invalid slave class %i\012"
net/bluetooth/af_bluetooth.c:574 [bluetooth]bt_sock_wait_ready =_ "sk %p\012"
net/bluetooth/af_bluetooth.c:537 [bluetooth]bt_sock_wait_state =_ "sk %p\012"
net/bluetooth/af_bluetooth.c:490 [bluetooth]bt_sock_ioctl =_ "sk %p cmd %x arg %lx\012"
net/bluetooth/af_bluetooth.c:446 [bluetooth]bt_sock_poll =_ "sock %p, sk %p\012"
net/bluetooth/af_bluetooth.c:330 [bluetooth]bt_sock_stream_recvmsg =_ "sk %p size %zu\012"
net/bluetooth/af_bluetooth.c:251 [bluetooth]bt_sock_recvmsg =_ "sock %p sk %p len %zu\012"
net/bluetooth/af_bluetooth.c:203 [bluetooth]bt_accept_dequeue =_ "sk %p, already unlinked\012"
net/bluetooth/af_bluetooth.c:189 [bluetooth]bt_accept_dequeue =_ "parent %p\012"
net/bluetooth/af_bluetooth.c:175 [bluetooth]bt_accept_unlink =_ "sk %p state %d\012"
net/bluetooth/af_bluetooth.c:159 [bluetooth]bt_accept_enqueue =_ "parent %p, sk %p\012"
net/bluetooth/hci_core.c:4263 [bluetooth]hci_cmd_work =_ "%s cmd_cnt %d cmd queued %d\012"
net/bluetooth/hci_core.c:4246 [bluetooth]hci_rx_work =_ "%s SCO data packet\012"
net/bluetooth/hci_core.c:4241 [bluetooth]hci_rx_work =_ "%s ACL data packet\012"
net/bluetooth/hci_core.c:4236 [bluetooth]hci_rx_work =_ "%s Event packet\012"
net/bluetooth/hci_core.c:4207 [bluetooth]hci_rx_work =_ "%s\012"
net/bluetooth/hci_core.c:4147 [bluetooth]hci_req_cmd_complete =_ "opcode 0x%04x status 0x%02x\012"
net/bluetooth/hci_core.c:4087 [bluetooth]hci_scodata_packet =_ "%s len %d handle 0x%4.4x\012"
net/bluetooth/hci_core.c:4054 [bluetooth]hci_acldata_packet =_ "%s len %d handle 0x%4.4x flags 0x%4.4x\012"
net/bluetooth/hci_core.c:4023 [bluetooth]hci_tx_work =_ "%s acl %d sco %d le %d\012"
net/bluetooth/hci_core.c:3991 [bluetooth]hci_sched_le =_ "chan %p skb %p len %d priority %u\012"
net/bluetooth/hci_core.c:3972 [bluetooth]hci_sched_le =_ "%s\012"
net/bluetooth/hci_core.c:3956 [bluetooth]hci_sched_esco =_ "skb %p len %d\012"
net/bluetooth/hci_core.c:3948 [bluetooth]hci_sched_esco =_ "%s\012"
net/bluetooth/hci_core.c:3932 [bluetooth]hci_sched_sco =_ "skb %p len %d\012"

I am using Ubuntu 16.04 LTS.

Answer 1

You misunderstand the purpose of that file. It doesn't represent the dynamic debug output. It's used to control the output. Reading the file shows you the things you can control with the facility. Writing it lets you specify what you wish to be displayed in the output.

See https://www.kernel.org/doc/html/v4.14/admin-guide/dynamic-debug-howto.html (or in your kernel source directory as .../Documentation/dynamic-debug-howto.txt)

...<debugfs>/dynamic_debug/control which can be read to display the complete list of known debug statements, to help guide you.