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Got some statistics information of our custom hardware to be displayed whenever user asks for using a command in the Linux user space. This implementation is currently uses PROC interface. We started adding more statistics information then we encountered a problem wherein the particular statistics command had to be executed twice for getting the entire data as PROC interface was restricted to 1 page.
As mentioned above the data transfer between the kernel and the user space is not critical but as per the data some decisions might be taken by the user. Our requirement for this interface design is that it should be capable of transferring amount of data maybe greater that 8192 bytes and the command needs to use minimal kernel resources (like locks etc.,) and it needs to be quick.
Using ioctl can solve the issue but since the command is exactly not controlling the device but to collect some statistics information, not sure whether it is a good mechanism to use as per Linux. We are currently using 3.4 kernel; not sure whether Netlink is lossy in this version (Previous versions I came across issues like when the queue becomes full, socket starts to drop data). mmap is another option . Can anyone suggest me what would be the best interface to use
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User space programs cannot access system resources directly so access is handled on the program's behalf by the operating system kernel. The user space programs typically make such requests of the operating system through system calls. Kernel threads, processes, stack do not mean the same thing.
The user application will be able to communicate with the kernel module and exchange data. The user application uses ioctl calls to send data to the kernel module. In the following example, these ioctl calls can be used to send application-specific details or send any updates at a later point of time.
The copy_to_user function copies a block of data from the kernel into user space. This function accepts a pointer to a user space buffer, a pointer to a kernel buffer, and a length defined in bytes. The function returns zero on success or non-zero to indicate the number of bytes that weren't transferred.
Netlink supports multicast communications between the kernel and multiple user-space processes, while ioctls are strictly one-to-one.
Netlink messages can be lost for various reasons (e.g. out of memory), while ioctls are generally more reliable due to their immediate-processing nature.
So If you asking for statistics to kernel from user space(application) it is more reliable and easy to use IOCTL while if you generate statistics in kernel space and you want your kernel space to send those data to user space(application) you have to use Netlink sockets.
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