I have a program that is listening to a certain event file handle. Is there a file I can read to get details about the specific event's device that I am listening to?
Assuming that (a) you're on Linux and (b) you have sysfs mounted (typically on /sys), you can look at /sys/class/input/eventX. This will be a symlink into the device tree; this should provide you some device details. For example:
$ readlink /sys/class/input/event4
../../devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4/2-1.4:1.1/input/input4/event4
For USB devices, you could then probably mount a usbfs filesystem and check out the devices file for more information.
Do you have access to the file descriptor or is this an external program? If this is your fd to the actual device, a list of ioctls provides you with most info you'll need. Have a look at print_device_info from evtest, it does exactly that:
http://cgit.freedesktop.org/evtest/tree/evtest.c#n753
Related
I would like to know the mechanism in which the Linux Kernel knows which file descriptor (e.g. /dev/input/eventX) to write the input to. For example, I know that when the user clicks the mouse, an interrupt occurs, which gets handled by the driver and propagated to the Linux input core via input_event (drivers/input/input.c), which eventually gets written to the appropriate file in /dev/input/. Specifically, I want to know which source files I need to go through to see how the kernel knows which file to write to based on the information given about the input event. My goal is to see if I can determine the file descriptors corresponding to specific input event codes before the kernel writes them to the /dev/input/eventX character files.
You may go through two files:
drivers/input/input.c
drivers/input/evdev.c
In evdev.c, evdev_init() will call input_register_handler() to initialize input_handler_list.
Then in an input device driver, after initialize input_dev, it will call:
input_register_device(input_dev)
-> get device kobj path, like /devices/soc/78ba000.i2c/i2c-6/6-0038/input/input2
-> input_attach_handler()
-> handler->connect(handler, dev, id);
-> evdev_connect()
In evdev_connect(), it will do below:
1. dynamic allocate a minor for a new evdev.
2. dev_set_name(&evdev->dev, "event%d", dev_no);
3. call input_register_handle() to connect input_dev and evdev->handle.
4. create a cdev, and call device_add().
After this, you will find input node /dev/input/eventX, X is value of dev_no.
Using wpa_supplicant 2.4 on ARM Debian.
Is there a way to get signal level, in decibels or percents, of the wireless network I’m currently connected to?
STATUS command only returns the following set of values: bssid, freq, ssid, id, mode, pairwise_cipher, group_cipher, key_mgmt, wpa_state, ip_address, p2p_device_address, address, uuid
I can run SCAN afterwards, wait for results and search by SSID. But that’s slow and error-prone, I'd like to do better.
The driver should already know that information (because connected, and adjusting transmit levels for energy saving), is there a way to just query for that?
This question is not about general computing hardware and software. I'm using wpa_supplicant through a C API defined in wpa_ctrl.h header, interacting with the service through a pair of unix domain sockets (one for commands, another one for unsolicited events).
One reason I don’t like my current SCAN + SCAN_RESULT solution, it doesn’t work for hidden SSID networks. Scan doesn’t find the network, therefore I’m not getting signal level this way. Another issue is minor visual glitch at application startup. My app is launched by systemd, After=multi-user.target. Unless it’s the very first launch, Linux is already connected to Wi-Fi by then. In my app’s GUI (the product will feature a touch screen), I render a phone-like status bar, that includes WiFi signal strength icon. Currently, it initially shows minimal level (I know it's connected because STATUS command shows SSID), only after ~1 second I’m getting CTRL-EVENT-SCAN-RESULTS event from wpa_supplicant, run SCAN_RESULT command and update signal strength to the correct value.
On the API level my code is straightforward. I have two threads for that, both call wpa_ctrl_open, the command thread calls wpa_ctrl_request, the event thread has an endless loop that calls poll passing wpa_ctrl_get_fd() descriptor and POLLIN event mask, followed by wpa_ctrl_pending and wpa_ctrl_recv.
And here's the list of files in /sys/class/net/wlan0:
./mtu
./type
./phys_port_name
./netdev_group
./flags
./power/control
./power/async
./power/runtime_enabled
./power/runtime_active_kids
./power/runtime_active_time
./power/autosuspend_delay_ms
./power/runtime_status
./power/runtime_usage
./power/runtime_suspended_time
./speed
./dormant
./name_assign_type
./proto_down
./addr_assign_type
./phys_switch_id
./dev_id
./duplex
./gro_flush_timeout
./iflink
./phys_port_id
./addr_len
./address
./operstate
./carrier_changes
./broadcast
./queues/rx-0/rps_flow_cnt
./queues/rx-0/rps_cpus
./queues/rx-1/rps_flow_cnt
./queues/rx-1/rps_cpus
./queues/rx-2/rps_flow_cnt
./queues/rx-2/rps_cpus
./queues/rx-3/rps_flow_cnt
./queues/rx-3/rps_cpus
./queues/tx-0/xps_cpus
./queues/tx-0/tx_maxrate
./queues/tx-0/tx_timeout
./queues/tx-0/byte_queue_limits/limit
./queues/tx-0/byte_queue_limits/limit_max
./queues/tx-0/byte_queue_limits/limit_min
./queues/tx-0/byte_queue_limits/hold_time
./queues/tx-0/byte_queue_limits/inflight
./queues/tx-1/xps_cpus
./queues/tx-1/tx_maxrate
./queues/tx-1/tx_timeout
./queues/tx-1/byte_queue_limits/limit
./queues/tx-1/byte_queue_limits/limit_max
./queues/tx-1/byte_queue_limits/limit_min
./queues/tx-1/byte_queue_limits/hold_time
./queues/tx-1/byte_queue_limits/inflight
./queues/tx-2/xps_cpus
./queues/tx-2/tx_maxrate
./queues/tx-2/tx_timeout
./queues/tx-2/byte_queue_limits/limit
./queues/tx-2/byte_queue_limits/limit_max
./queues/tx-2/byte_queue_limits/limit_min
./queues/tx-2/byte_queue_limits/hold_time
./queues/tx-2/byte_queue_limits/inflight
./queues/tx-3/xps_cpus
./queues/tx-3/tx_maxrate
./queues/tx-3/tx_timeout
./queues/tx-3/byte_queue_limits/limit
./queues/tx-3/byte_queue_limits/limit_max
./queues/tx-3/byte_queue_limits/limit_min
./queues/tx-3/byte_queue_limits/hold_time
./queues/tx-3/byte_queue_limits/inflight
./tx_queue_len
./uevent
./statistics/rx_fifo_errors
./statistics/collisions
./statistics/rx_errors
./statistics/rx_compressed
./statistics/rx_dropped
./statistics/tx_packets
./statistics/tx_errors
./statistics/rx_missed_errors
./statistics/rx_over_errors
./statistics/tx_carrier_errors
./statistics/tx_heartbeat_errors
./statistics/rx_crc_errors
./statistics/multicast
./statistics/tx_fifo_errors
./statistics/tx_aborted_errors
./statistics/rx_bytes
./statistics/tx_compressed
./statistics/tx_dropped
./statistics/rx_packets
./statistics/tx_bytes
./statistics/tx_window_errors
./statistics/rx_frame_errors
./statistics/rx_length_errors
./dev_port
./ifalias
./ifindex
./link_mode
./carrier
You can get the signal level of the connected wifi by wpa_supplicant cmd SIGNAL_POLL
The wpa_supplicant would return:
RSSI=-60
LINKSPEED=867
NOISE=9999
FREQUENCY=5745
The value of the RSSI is the signal level.
You can get the signal level of the connected wifi by wpa_supplicant cmd BSS <bssid>.
About the bssid of the connected wifi, you can get from wpa_supplicant cmd STATUS.
https://android.googlesource.com/platform/external/wpa_supplicant_8/+/622b66d6efd0cccfeb8623184fadf2f76e7e8206/wpa_supplicant/ctrl_iface.c#1986
For iw compatible devices:
Following command gives the current station(aka AP) signal strength:
iw dev wlp2s0 station dump -v
If you need C API, just dig the source code of iw.
After a quick glance, the function you need is here
For broadcom devices, try search broadcom wl. It is close source, don't know if C API is provided.
What are the differences between ID_SERIAL and ID_SERIAL_SHORT udev properties. How udev is assigning values for these 2 udev property IDs. I am writing USB driver and I am using udev_device_get_property_value() method to get values for udev properties. in this case I can see there are 2 similar attributes as mentioned above. I couldn't find an explaining document for these information.
The ID_SERIAL_SHORT value comes from the iSerial string (if present) in the USB device descriptor. The ID_SERIAL value is constructed in software and made up from various strings (vendor or manufacturer, model or product, and serial number if present) separated with _.
You can use udevadm info [DEVPATH|FILE] command to look at the udev properties (specifying a specific DEVPATH or FILE as appropriate).
I've added a MAX7320 i2c expander chip to i2c bus 0 on my ARM Linux board.
The chip works correctly from userspace with commands such as /usr/sbin/i2cset -y 0 0x5d 0x02 and /usr/sbin/i2cget -y 0 0x5d.
There is a drivers/gpio/gpio-max732x.c file in the kernel source, which is compiled into the kernel that I'm running. (I've built it from source.)
How do I tell the kernel that it should instantiate the gpio-max732x driver on "i2c bus 0, chip id 0x5d"?
Do I need to modify the device tree .dts file and put a new .dtb file in /boot/dtbs/?
What would the clause for instantiating a gpio-max732x module look like?
P.S. I've seen https://lkml.org/lkml/2015/1/13/305 but I can't figure out how to get the patch files.
Device Tree
There must be appropriate Device Tree definition for your chip, in order for driver to instantiate. There are 2 ways to do so:
Modify .dts Device Tree file for your board (look in arch/arm/boot/dts/), then recompile it and re-flash it to your device.
This way is preferred in case when you have access you kernel sources for your board and you are able to re-flash .dtb file to your device.
Create Device Tree Overlay file, compile it and load it on your device.
This way is preferred when you don't have access to kernel sources for your board, or you are unable to flash new device tree blob to your device.
Your device definition in Device Tree should look like (according to Documentation/devicetree/bindings/gpio/gpio-max732x.txt):
&i2c0 {
expander: max7320#5d {
compatible = "maxim,max7320";
reg = <0x5d>;
gpio-controller;
#gpio-cells = <2>;
};
};
Kernel configuration
As your expander chip (MAX7320) has no input GPIOs, you don't need IRQ support for MAX732x. So you can disable CONFIG_GPIO_MAX732X_IRQ in your kernel configuration.
Matching device with driver
Once you have your Device Tree loaded (with definition for MAX7320), MAX732x driver will be matched with device definition, and instantiated. Below is explained how matching happens.
In Device Tree file you have compatible property:
compatible = "maxim,max7320";
In MAX732x driver you can see this table:
static const struct of_device_id max732x_of_table[] = {
...
{ .compatible = "maxim,max7320" },
...
When driver is being loaded, and when Device Tree blob is being loaded, kernel tries to find the match for each driver and Device Tree definition. Just by comparing strings above. If strings are matched -- kernel instantiates driver, passing corresponding device parameters to it. Look at i2c_device_match() function for details.
Obtaining patches
The best way is to use kernel sources that already have Device Tree support of MAX732x (v4.0+). But if it's not the case, then...
You can cherry-pick patches from upstream kernel to your kernel:
$ git remote add upstream git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
$ git fetch --all
$ git cherry-pick 43c4bcf9425e
$ git cherry-pick 479f8a5744d8
$ git cherry-pick 09afa276d52e
$ git cherry-pick 996bd13f28e6
And if you still want to apply patches manually (worst option, actually), here you can find direct links to patches. Click (patch) link to get a raw patch.
Also check later patches for gpio-max732x.c here.
Hardware concerns
To be sure that your chip has 0x5d I2C address, check that configuration pins are tied to next lines (as per datasheet):
Pin Line
-----------
AD2 V+
AD0 V+
Recently, I developed a simple file system kernel module.
So, I needed to assign my own ioctl function (.unlocked_ioctl) to the file_operation structure to implement specific commands to my file system module. The Ext4 file system has its own ioctl function, for example.
Then, I created a file using the dd command and mounted it:
# mount -t myfs -o loop simple_file /mnt/
Everything works fine, but how can I access this file system using ioctl with a user space program?
I tryed to do ioctl(fd, MY_COMMAND_1, &my_struct_t); (where fd is the file descriptor of the dev file /dev/loop[0..7]), but it returns me Invalid argument.
If you open /dev/loop0, you're accessing a loop device, and therefore you're talking to the loop driver.
The ioctl handler that you've registered for your filesystem applies to files opened on a mounted filesystem.
fd = open("/mnt/something", O_RDWR);
ioctl(fd, MY_COMMAND_1, &my_struct_t);