ioctl | The missing tool to call arbitrary ioctls on devices

I am trying to use the write protection feature of Linux's userfaultfd, but it does not appear to be enabled in my kernel even though I am using version 5.13 (write protection should be fully supported in 5.10+).

When I run

I have to modify a driver that runs on linux to add a callback function that is invoked from an external application. I already have the code implemented but when it is executed when the computer starts up, the system gives an error and is blocked.

This is my new code on the driver side:

I've got this power monitor that I'm attempting to interface with to retrieve it's fault log LTC2977 (data sheet: https://www.analog.com/media/en/technical-documentation/data-sheets/ltc2977.pdf)

I'm new to i2c / pmbus / smbus things so forgive my poor terminology or incorrect descriptions of how things work. On page 18 the data sheet states that I can interface with it like so:

The LTC2977 is a slave device. The master can communicate with the LTC2977 using the following formats:

• Master transmitter, slave receiver
• Master receiver, slave transmitter

The following SMBus protocols are supported:

• Write Byte, Write Word, Send Byte
• Read Byte, Read Word, Block Read
• Alert Response Address

Figure 1a-12 illustrate the aforementioned SMBus protocols. All transactions support PEC (packet error check) and GCP (group command protocol). The Block Read supports 255 bytes of returned data. For this reason, the PMBus timeout may be extended using the Mfr_config_all_ longer_pmbus_timeout setting.

The log in question can be accessed with SMBus (PMBus?) command 0xEE, wherein it will spit out 0xFF followed by 255 bytes containing the log data. Now I can see the device and all its internal commands/registers(?) by doing i2cdump, and similarly if I do i2cget ... 0xEE I get the output 0xff, which is what the first entry in the log is supposed to be. I can also do i2cget ... 0xEE w, so outputting as a word to get 0x--ff where the '-'s are values changing everytime I call i2cget, my log data perhaps?

My problem is I'm attempting to read this as a block like the document stated I could do above. I'm not entirely sure how to do this so I tried the following:

I am trying to realize DMA in Xilinx, using DMA Engine. FPGA guys give me an AXI DMA IP-Core with DMA support, so I need to write a driver, which will transfer data from kernel to user space buffer. Here you can find an example of the driver and app, which works so:

The following program uses a PF_PACKET socket to send a TCP SYN packet to web server read from a file which is a list of web server IPv4 addresses - one address per line. The code is quite long because it takes a lot of code to obtain the gateway router MAC and IP address necessary for filling in the ethernet and IP headers. The good news is you can just skip all the functions in the preamble and just go to main which is where the problem is.

My program works perfectly for the first iteration of the while loop in main. Here is the output:

Hello experts i am using InAppWebView plugin for loading web from the assets folder when i run it on debug mode its working fine when used release mode app show blank page any expert know this issue i am trying find there solution everywhere but no solution fine if any friend can help i will appreciate him?

You have done it a thousand times: you unplug some USB equipment and any device associated with that USB equipment is removed by the driver. Any program that uses some previously opened file handle will get an error. Somehow most Linux drivers take care of that.

I am currently struggling to implement the same in a simple driver. My driver creates a character device. When the device is opened, I set the private_data member of struct file to the address of some management data that exists once per character device. That management data also includes a mutex that I use to synchronize operations like read, write, and ioctl.

The problem now arises when the USB equipment is unplugged. I must not free the memory where that management data lives. First, any currently running read, write, or ioctl should finish. Any such running call will likely also hold a lock on the mutex and will attempt to unlock it. So the memory where the mutex lives will be accessed.

Any read, write, or ioctl call subsequent to unplugging the equipment should fail, so every such call must read some variable telling whether the USB equipment is still plugged in or not. Again, that variable must live somewhere and the memory where it lives must stay allocated as long as there are open file handles.

Long story short, it seems to me that I must do some sort reference counting: The management data must stay allocated until all file handles have been closed. I could implement that myself, but I have the feeling that I would reinvent the wheel. Such a thing must already exist, I'm not the first to have this problem.

Does Linux internally keep track of the number of open file handles? Can I define a callback that is called when all file handles have been closed? Is that even a viable thing? What is the proper way to remove a character device from the system?

Global variables shall not be avoided, since any number of USB devices can be attached.

I'm trying to use C/C++ to communicate with a CAN bus. I'm using sockets to read and write on the bus. I've created a write thread and a read thread. The read thread is constantly trying to read and the socket, and when a write request arrives, the write thread take control of the socket using a mutex and do the write.

I'm having a big issue with speed using this method, as a write request can sometimes take 500 ms to be completed (which is completely unfeasible for my application). I've tried to put a timeout on the read command to make it non-blocking when nothing comes on the bus, but if the timeout is too short, I have reliability issues with the read. On the other hand, if I make it too long, the speed increase is insufficient.

It's my first time working with CAN. Would you have some advices on implementation of fast, two-way CAN communication node in C/C++ ? Which library should I use to interface with the bus itself ? Which architecture would yield the lowest read and write latency ?

To give a few metrics for the application, the bus bitrate is 1MBits/sec, I'm using CAN-Open with 64 bits data packets (each message contains 32 bits for indexes and 32 bits of data). I would like a write frequency from 300 to 500hz, same for the read frequency.

Thanks a lot for your help !

EDIT :

Thanks a lot for all your comments. Here are some clarifications on my application and problems.

I'm working on a mobile robot project, and I'm using CAN-Open to communicate with motor drivers and sensors. The code will run on a Raspberry Pi CM4 running Raspbian OS mounted on a custom IO board integrating a MCP2515 CAN controller. I want to implement fast communication interface between the ROS architecture and the CAN bus. The language used could be either C or C++.

I'm currently using a homemade interface build around standard C sockets, but the speed is very low, and is a big bottleneck to the robot's performance. So I'm looking for a better solution, either:

• An open-source library build for this purpose
• Architecture suggestion to implement such a program
• A combination of both

Here are the socket creation, the read and the write functions I use. Read and write being each called in a while loop in different threads (I'm using pthread):

Thank you for watching this.

I'm having difficulties with my BBB on CAN communication like for months... I'd be really pleased if you could give me just a little help!

I'm working on CAN protocol between BBB and another CAN device. The another device is confirmed to be working alright with CAN. I'm using my BBB with Cloud9 platform on windows laptop, and on the another device, it's using CAN0.

I have set the 'config-pin' on BBB like below using CAN1, and I tried 'cansend' utility. The bitratre value on the another device is also set to be equal.