11/24/2023 0 Comments Listhead linux kernel example![]() What I'm doing wrong? I need that the key be the same name present in the struct h_node. My first question is: Why our struct has to have the struct h_list inside it? If we're gonna access our struct through the struct h_list our struct shouldn't be within struct h_list and not the opposite? After reading the tutorial I've tried to write the following code: DECLARE_HASHTABLE(nodes_hash, 3)Ĭhar name /*The key is the name of lua state*/īut this does not even compile. If (list_empty(&mydrv_wq.I'm trying to understand and use the kernel hash tables and I've already read this and this link, but I didn't understand none of them. Look at Figure 3.1 to see the physical structure of the work list.įigure 3.1. It uses list_add_tail() to add a work function to the tail of the list. Listing 3.3 implements a function that other parts of the kernel can use to submit work. See Listing 3.4 */ĬLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD) īefore examining the worker thread that executes submitted work, let's look at work submission itself. INIT_LIST_HEAD(&mydrv_wq.mydrv_worklist) * Initialize the wait queue for communication * Initialize the lock to protect against The driver initialization routine mydrv_init() in Listing 3.2 initializes the spinlock, the list head, and the wait queue, and kick starts the worker thread. This is done using a spinlock that is also a part of mydrv_wq. The list helper functions do not protect accesses to list members, so you need to use concurrency mechanisms to serialize simultaneous pointer references. Its members include a pointer to the head of the work list, and a wait queue to communicate between driver functions that submit work and the kernel thread that performs the work. Mydrv_wq is global to all work submissions. Void *worker_data /* Argument to worker_func */ Void (*worker_func)(void *) /* Work to perform */ Struct list_head mydrv_workitem /* The work chain */ Wait_queue_head_t todo /* Synchronize submitter Struct list_head mydrv_worklist /* Work List */ Let's first introduce the key driver data structures used by our example: Before understanding this example, however, be aware that we will use the work queue interface in Listing 3.5 to implement the same task in a simpler manner. Of course, the rest of the driver needs to be designed to suit this scheme of deferred execution. The driver submits work functions to the tail of the list, while the kernel thread ploughs its way from the head of the list, thus ensuring that work queued first gets done first. The actual work is performed by a kernel thread, which traverses the list and executes the work functions in the background. ![]() So, whenever the driver needs to perform this expensive work, it defers execution by adding the corresponding routine to a linked list of work functions. Naturally, your driver doesn't like to block until the task finishes, because that slows down the responsiveness of applications relying on it. ![]() An example is a task that forces the calling thread to sleep-wait. Assume that your kernel driver needs to perform a heavy-duty task from an entry point. The example also serves as a foundation to understand the concept of work queues, which is discussed in the next section. To illustrate list usage, let's implement an example. Checks whether there are any elements in the list
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