Struct kref linux. Aug 21, 2019 · 在Linux内核中，使用了struct kref这个结构体来进行对象管理的引用计数，对该结构体的操作为“原子”操作，常用的函数接口有用来初始化引用计数器的kref_init ()、引用计数加1操作的kref_get ()和引用计数减1操作的kref_put ()，通过引用计数，能够方便地进行对象管理。 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Allocation ¶ The first thing a driver needs to do is to allocate a struct tty_driver. This material is adapted from a tutorial document, so the alert reader may notice a few departures from the typical standards-document style. For example, if you allocate some data and then pass it to another thread to process: Rather than having kernel code implement its own reference counting via atomic_t types and simple "get" and "put" wrapper functions, developers are encouraged to use the kref type and its helpers to provide a common and known-correct reference counting mechanism in the kernel. It deserves a cross however because the kref only encapsulates part of the story about reference counting. This is done by tty_alloc_driver() (or __tty_alloc_driver()). pdf”和描述“kref_example, struct kref, reference counting made easy”表明该文件很可能是关于Linux内核编程中kref引用计数机制的一个实例或教程。 kref是一种用于管理内核对象引用计数的数据 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Members of tty_struct are documented in TTY Struct Jul 11, 2013 · It's strange that struct cdev has struct kobject member, do any body knows the reason? Sep 6, 2020 · Yes, looks like kref_read is the right way to go. Dec 19, 2007 · If all that you want to use a kobject for is to provide a reference counter for your structure, please use the struct kref instead; a kobject would be overkill. to construct name If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). There are May 8, 2010 · } But note that the struct kref member needs to remain in valid memory for a rcu grace period after release_entry_rcu was called. This is done by tty_alloc_driver () (or __tty_alloc_driver()). For example, if you allocate some data and then pass it to another thread to process: Source code of linux/include/linux/kref. The caller must hold sufficient locks/counts to ensure that their existing reference cannot go away void tty_kref_put(struct tty_struct *tty) release a tty kref Parameters struct tty_struct *tty tty device Description Release a reference to the tty device and if need be let the kref layer destruct the 这将kref中的refcount设置为1。 Kref规则 一旦你有一个初始化的kref，你必须遵循以下规则: 如果你对一个指针做了一个非临时性的拷贝，特别是如果它可以被传递给另一个执 行线程，你必须在传递之前用kref_get ()增加refcount: In future releases of the Linux kernel, the struct kobject will probably loose its in-ternal reference count and use the struct kref instead. At the core of a kref is an atomic_t counter which contains the number of outstanding references. For example, if you allocate some data and then pass it to another thread to process: Sep 18, 2025 · Bluetooth: L2CAP: Fix user-after-free This uses l2cap_chan_hold_unless_zero () after calling __l2cap_get_chan_blah () to prevent the following trace: Bluetooth: l2cap_core. 转自： Linux内核引用计数器kref结构 - liangliangge - 博客园 1、前言 struct kref结构体 是一个引用计数器，它被嵌套进其它的结构体中，记录所嵌套结构的引用计数。引用计数用于检测内核中有多少地方使用了某个对象，每当内核的一个部分需要某个对象所包含的信息时，则该对象的引用计数加1，如果不 Dec 19, 2007 · If all that you want to use a kobject for is to provide a reference counter for your structure, please use the struct kref instead; a kobject would be overkill. 对于规则一，其实主要是针对多条执行路径（比如另起一个线程）的情况。 Linux kernel source tree. static inline unsigned int kref_read(const struct kref *kref) { return refcount_read(&kref->refcount); } Jul 3, 2013 · Reference counting is used by the kernel to know when a data structure is unused and can be disposed of. If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). It brings an OO-like programming style to the kernel, and is mainly used for reference - Selection from Linux Device Drivers Development [Book] TTY Struct ¶ Initialization Name Reference counting Install Read & Write Start & Stop Wakeup Hangup Misc TTY Struct Flags TTY Struct Reference struct tty_struct is allocated by the TTY layer upon the first open of the TTY device and released after the last close. txt blob: ddf85a5dde0c12a435b9cbcc30f44159de5acc0b [file] [log] [blame] Dec 9, 2023 · 这将将kref中的refcount设置为1。 Kref规则 一旦您有了初始化的kref，您必须遵循以下规则： 如果您复制指针的非临时副本，特别是如果它可以传递给另一个执行线程，则必须在传递之前使用kref_get ()增加引用计数： Linux kernel source tree. So, how does it helps to map these structures? Given below is a pragraph from ULK 3rd 这将kref中的refcount设置为1。 Kref规则 一旦你有一个初始化的kref，你必须遵循以下规则: 如果你对一个指针做了一个非临时性的拷贝，特别是如果它可以被传递给另一个执 行线程，你必须在传递之前用kref_get ()增加refcount: The caller must hold sufficient locks/counts to ensure that their existing reference cannot go away void tty_kref_put(struct tty_struct *tty) ¶ release a tty kref Parameters struct tty_struct *tty tty device Description Release a reference to the tty device and if need be let the kref layer destruct the object for us. kernel. Abstract This document describes several reference-counting disciplines used in the Linux kernel, and con-cludes by summarizing the memory-barrier, atomic-instruction, and compiler-control required by each. c:static void l2cap_chan_destroy (struct kref *kref) Bluetooth: chan 0000000023c4974d Bluetooth: parent 00000000ae861c08 Jul 14, 2004 · The " kref " mechanism is a simple structure for implementing reference-counted objects in the kernel; it was covered here last March. h kobject structure kobject is the core of the device model, running behind the scenes. See TTY Driver Reference at the end of this document on what actually shall be filled in. That means, dropping the data from the outpu buffer on the device and waiting for sending logic to finish. Mar 13, 2004 · In thinking about people's complaints about the current kobject interface, a lot of people don't like the "complexity" of what is necessary to use a kobject. . For example, if you allocate some data and then pass it to another thread to process: Feb 9, 2014 · The latest kref document from linux kernel can be found: https://www. 5w次，点赞9次，收藏32次。本文介绍了Linux内核中的kref机制，一种用于管理复杂结构引用计数的方法。文章详细解释了kref的实现原理，包括其核心函数kref_get和kref_put的工作流程，并提供了具体的使用案例。 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Creating “simple” kobjects ¶ 标题“kref_example. 4 204/342] drm/dp/mst: deallocate payload on port destruction Greg Kroah-Hartman Tue, 01 Mar 2016 16:46:03 -0800 在Linux内核里，引用计数是通过struct kref结构来实现的。 在介绍如何使用kref之前，我们先来假设一个情景。 假如您开发的是一个 字符设备 驱动，当设备插上时，系统自动建立一个设备节点，用户通过文件操作来访问设备节点。 Aug 6, 2021 · 文章浏览阅读1k次。本文详细介绍了Linux内核如何通过kref结构进行内存管理，特别是对于设备驱动中的对象生命周期管理。kref通过引用计数确保在多线程环境下正确释放资源，避免内存泄漏。文章通过实例代码解释了kref的使用规则，包括kref_init、kref_get和kref_put函数，并强调了使用kref时必须遵循的三 [PATCH 06/12] PM / OPP: Add 'struct kref' to struct dev_pm_opp If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). 7k次。本文详细解析了Linux内核中的引用计数机制，包括kref结构的使用，kref_init、kref_get和kref_put函数的功能，以及如何在内核结构中嵌入kref实现内存对象的安全管理和释放。 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). This runs under the tty_mutex currently so we can be relaxed about ordering. Refcount mechanisms in the Linux kernel typically employ a simple data structure called struct kref which encapsulates an integer as the real counter, and provide APIs (e. The rest of close handling is performed in tty_port_close_end While studying Understanding The Linux Kernel I came across reference counter in Kobject structure and container. For example, if you allocate some data and then pass it to another thread to process: TTY Driver and TTY Operations ¶ Allocation TTY Driver Flags Registration Registering Devices Linking Devices to Ports TTY Driver Reference TTY Operations Reference Allocation ¶ The first thing a driver needs to do is to allocate a struct tty_driver. See TTY Driver If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Creating “simple” kobjects ¶ May 15, 2025 · kref 相关的代码实现主要在 include/linux/kref. h linux v6. The struct kref structure is a reference counter, which is nested into other structures to record the reference count of the nested structure. The TTY layer passes this structure to most of struct tty_operation ’s hooks. Note the specific put_char operation in the driver layer may go away soon. * With a lookup followed by a kref_get_unless_zero *with return value check* * locking in the kref_put path can be deferred to the actual removal from * the lookup structure and RCU lookups become trivial. h 中。 1、kref 数据结构 1）struct kref 可以看到， kref 的结构体中包含了一个 refcount_t 类型，也就是 atomic_t 类型的计数值。 atomic_t 是原子操作，操作时有专用的 API 函数，它在一定程度上可以解决内核的并发和竞态问题，省去额外加锁去锁的过程。（include/linux 引言 ¶ krefs 允许你为对象添加引用计数器。如果你的对象在多个地方使用并传递，并且没有引用计数，那么你的代码几乎肯定是有问题的。如果你需要引用计数，krefs 是一个好方法。 要使用 kref，请像这样将其添加到你的数据结构中： If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). 16-r on KDAB Codebrowser TTY Struct ¶ Initialization Name Reference counting Install Read & Write Start & Stop Wakeup Hangup Misc TTY Struct Flags TTY Struct Reference struct tty_struct is allocated by the TTY layer upon the first open of the TTY device and released after the last close. Earlier the struct kref had a release field, but all uses turned out to be such that the caller knew the appropriate release function, so that it could be a parameter of kref_put (), saving memory. That can be accomplished by using kfree_rcu(entry, rhead) as done above, or by calling synchronize_rcu() before using kfree, but note that synchronize_rcu() may sleep for a substantial amount of time. Introducing struct kref. Dec 17, 2024 · 文章浏览阅读1. If this happens, struct kref might have to be changed in order to support passing the release callback as a pa-rameter to the kref_put function, in order to save the storage size of the function pointer If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). Jan 10, 2013 · The documentation for this struct was generated from the following file: include/linux/ of. The TTY layer passes this structure to most of struct tty_operation’s hooks. txt The first example in this document is repeated as following: void data_release (struct kr If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). , kref_get and kref_put) for manipulating the counter [13]. If all you want is something to handle reference counting properly, a kobject can seem a bit "large". org/doc/Documentation/kref. Members of tty_struct are documented in TTY Struct If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). kobjects At the heart of the device model is the kobject, which is represented by struct kobject and defined in <linux/kobject. For example, if you allocate some data and then pass it to another thread to process: structtty_struct is allocated by the TTY layer upon the first open of the TTY device and released after the last close. A tiny (only 8 bytes on a 32bit platform) that will properly Jan 10, 2013 · The documentation for this struct was generated from the following file: include/linux/ kref. Mar 16, 2004 · struct kref { atomic_t refcount; void (*release)(struct kref *kref); }; A kref comes with the usual functions one would expect: kref_init () to set it up, and kref_get () and kref_put () to manage the reference count. For more information on how to use struct kref, please see the file Adding reference counters (krefs) to kernel objects in the Linux kernel source tree. The kobject is similar to the Object class in object-oriented languages such as C# or Java. For example, if you allocate some data and then pass it to another thread to process: Jun 8, 2009 · This inclusion of kref in the Linux kernel gives both a tick and a cross to the kernel in terms of explicit support for design patterns. A tick is deserved as the kref clearly embodies an important design pattern, is well documented, and is clearly visible in the code when used. Parameters struct tty_port *port tty_port of the device struct tty_struct *tty tty being closed struct file *filp passed file pointer Description Decrements and checks open count. } But note that the struct kref member needs to remain in valid memory for a rcu grace period after release_entry_rcu was called. Parameters struct tty_struct *tty tty unsigned char ch character to write Description Write one byte to the tty using the provided tty->ops->put_char () method if present. h>. For example, if you allocate some data and then pass it to another thread to process: Linux kernel source tree. Jun 17, 2013 · If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). @@ -32,12 +29,12 @@ struct kref { */ static inline void kref_init (struct kref *kref) { - atomic_set (&kref->refcount, 1); + refcount_set (&kref->refcount, 1 TTY Struct ¶ Initialization Name Reference counting Install Read & Write Start & Stop Wakeup Hangup Misc TTY Struct Flags TTY Struct Reference struct tty_struct is allocated by the TTY layer upon the first open of the TTY device and released after the last close. In future releases of the Linux kernel, the struct kobject will probably loose its in-ternal reference count and use the struct kref instead. Next, the newly allocated structure is filled with information. * * Return: non-zero if the increment succeeded. All told, it's quite simple. For example, if you allocate some data and then pass it to another thread to process: Jun 26, 2020 · 文章浏览阅读1. It provides basic facilities, such as reference counting, a name, and a parent pointer, allowing the creation of a hierarchy of objects. For example, if you allocate some data and then pass it to another thread to process: Mar 1, 2016 · [PATCH 4. ) index index of this tty (e. For example, if you allocate some data and then pass it to another thread to process: 这将kref中的refcount设置为1。 Kref规则 ¶ 一旦你有一个初始化的kref，你必须遵循以下规则: 如果你对一个指针做了一个非临时性的拷贝，特别是如果它可以被传递给另一个执 行线程，你必须在传递之前用 kref_get() 增加refcount: If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). Members of tty_struct are documented in TTY Struct 一、介绍 在 Linux 内核中，kref（kernel reference counting）是一种用于管理对象引用计数的机制。 引用对象时，kref 计数加 1； 引用结束时，kref 计数减 1； 当 kref 计数为 0 时，调用资源释放的回调接口释放对象。 Sep 13, 2025 · 文章浏览阅读3. h 这会将 kref 中的引用计数设置为 1。 Kref 规则 ¶ 一旦你拥有一个已初始化的 kref，你必须遵循以下规则： 如果你创建了指针的非临时副本，特别是当它可以传递给另一个执行线程时，你必须在将其传递出去之前使用 kref_get() 增加引用计数。 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). Without further ado: struct kobject Members magic magic value set early in alloc_tty_struct to TTY_MAGIC, for debugging purposes kref reference counting by tty_kref_get() and tty_kref_put(), reaching zero frees the structure dev class device or NULL (e. g. Don't call it directly, use this method Return the number of characters successfully output. 9k次。 引用计数优点：具有实时性，一旦变量没有被引用，就会把变量给释放掉kref机制：是linux内核中使用的引用计数机制，下面介绍一下，在内核中该如何使用引用计数这个技术，首先，在设计自己的数据结构时，要包含struct kref结构的字段。 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). For all of those people, this patch is for you. Contribute to torvalds/linux development by creating an account on GitHub. For example, if you allocate some data and then pass it to another thread to process: This pointer is required, and it is not acceptable to pass kfree 函数原型： static inline int kref_put (struct kref *kref, void (*release) (struct kref *kref)) code / linux / torvalds / linux / 13c42c2f43b19aab3195f2d357db00d1e885eaa8 / . Creating “simple” kobjects ¶ 这将kref中的refcount设置为1。 Kref规则 ¶ 一旦你有一个初始化的kref，你必须遵循以下规则: 如果你对一个指针做了一个非临时性的拷贝，特别是如果它可以被传递给另一个执 行线程，你必须在传递之前用 kref_get() 增加refcount: In future releases of the Linux kernel, the struct kobject will probably loose its in-ternal reference count and use the struct kref instead. Furthermore, RCU implementations become extremely tricky. If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). The allocation routines expect a number of devices the driver can handle at most and flags TTY Struct ¶ Initialization Name Reference counting Install Read & Write Start & Stop Wakeup Hangup Misc TTY Struct Flags TTY Struct Reference struct tty_struct is allocated by the TTY layer upon the first open of the TTY device and released after the last close. This guide is… Mar 7, 2014 · 参考原文链接：linux内核部件分析（三）——记录生命周期的kref另外关于kref的使用可参考：Linux内核里的“智能指针”Linux内核里的“智能指针” (续) kref是一个引用计数器，它被嵌套进其它的结构中，记录所嵌套结构的引用计数，并在计数为0时调用相应的清理函数。kref的原理和实现都非常简单，但 If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put () cannot occur during the kref_get (), and the structure must remain valid during the kref_get (). That can be accomplished by using kfree_rcu (entry, rhead) as done above, or by calling synchronize_rcu() before using kfree, but note that synchronize_rcu() may sleep for a substantial amount of time. 简介 ¶ krefs允许你为你的对象添加引用计数器。如果你有在多个地方使用和传递的对象， 而你没有refcounts，你的代码几乎肯定是坏的。如果你想要引用计数，krefs是个 好办法。 要使用kref，请在你的数据结构中添加一个，如: If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Return a new reference to a tty object. Members of tty_struct are documented in TTY Struct Reference at the bottom. For example, if you allocate some data and then pass it to another thread to process: 简介 ¶ krefs允许你为你的对象添加引用计数器。如果你有在多个地方使用和传递的对象， 而你没有refcounts，你的代码几乎肯定是坏的。如果你想要引用计数，krefs是个 好办法。 要使用kref，请在你的数据结构中添加一个，如: Parameters struct tty_struct *tty the tty to set up Description Initialise the termios structure for this tty. / Documentation / kref. Still, it is a useful abstraction: it has far fewer methods, so reasoning about it is simpler. Jan 10, 2013 · 64 static inline int kref_sub (struct kref *kref, unsigned int count, If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). Flushes the port if this is the last close. If all that you want to use a kobject for is to provide a reference counter for your structure, please use the struct kref instead; a kobject would be overkill. Creating “simple” kobjects ¶ Jun 27, 2019 · Linux驱动开发杂记 (0x19) - 内核中的引用计数器kref kref是一个引用计数器，它被嵌套进其它的结构中，记录所嵌套结构的引用计数，并在计数清零时调用相应的清理函数。 Jan 17, 2024 · Sysfs, a critical component of the Linux kernel, provides a dynamic and intuitive interface to kernel data structures. Most of the time, reference counts are represented by an atomic_t variable, perhaps wrapped by a structure like a kref. Once that count drops to zero, the release function is called to clean things up. But note that the struct kref member needs to remain in valid memory for a rcu grace period after release_entry_rcu was called. } kref_put 此接口，额外支持在 refcnt 减为0时，主动调用一个 release callback static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref)) { if (refcount_dec_and_test(&kref->refcount)) { release(kref); return 1; } return 0; } kref_put_mutex (lock) 等同于 refcount_dec_and_mutex_lock 额外支持调用 Thus, today a struct kref is just an atomic_t. The reference count is used to detect how many places in the kernel use an object. Members of tty_struct are documented in TTY Struct If the code attempts to gain a reference to a kref-ed structure without already holding a valid pointer, it must serialize access where a kref_put() cannot occur during the kref_get(), and the structure must remain valid during the kref_get(). ptys, serdev) driver struct tty_driver operating this tty ops struct tty_operations of driver for this tty (open, close, etc. p78e jzyzqer za nnff zmwz ezzfgc ia hiq yaagtr2 t57p4