From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- Documentation/core-api/kobject.rst | 434 +++++++++++++++++++++++++++++++++++++ 1 file changed, 434 insertions(+) create mode 100644 Documentation/core-api/kobject.rst (limited to 'Documentation/core-api/kobject.rst') diff --git a/Documentation/core-api/kobject.rst b/Documentation/core-api/kobject.rst new file mode 100644 index 000000000..731024731 --- /dev/null +++ b/Documentation/core-api/kobject.rst @@ -0,0 +1,434 @@ +===================================================================== +Everything you never wanted to know about kobjects, ksets, and ktypes +===================================================================== + +:Author: Greg Kroah-Hartman +:Last updated: December 19, 2007 + +Based on an original article by Jon Corbet for lwn.net written October 1, +2003 and located at https://lwn.net/Articles/51437/ + +Part of the difficulty in understanding the driver model - and the kobject +abstraction upon which it is built - is that there is no obvious starting +place. Dealing with kobjects requires understanding a few different types, +all of which make reference to each other. In an attempt to make things +easier, we'll take a multi-pass approach, starting with vague terms and +adding detail as we go. To that end, here are some quick definitions of +some terms we will be working with. + + - A kobject is an object of type struct kobject. Kobjects have a name + and a reference count. A kobject also has a parent pointer (allowing + objects to be arranged into hierarchies), a specific type, and, + usually, a representation in the sysfs virtual filesystem. + + Kobjects are generally not interesting on their own; instead, they are + usually embedded within some other structure which contains the stuff + the code is really interested in. + + No structure should **EVER** have more than one kobject embedded within it. + If it does, the reference counting for the object is sure to be messed + up and incorrect, and your code will be buggy. So do not do this. + + - A ktype is the type of object that embeds a kobject. Every structure + that embeds a kobject needs a corresponding ktype. The ktype controls + what happens to the kobject when it is created and destroyed. + + - A kset is a group of kobjects. These kobjects can be of the same ktype + or belong to different ktypes. The kset is the basic container type for + collections of kobjects. Ksets contain their own kobjects, but you can + safely ignore that implementation detail as the kset core code handles + this kobject automatically. + + When you see a sysfs directory full of other directories, generally each + of those directories corresponds to a kobject in the same kset. + +We'll look at how to create and manipulate all of these types. A bottom-up +approach will be taken, so we'll go back to kobjects. + + +Embedding kobjects +================== + +It is rare for kernel code to create a standalone kobject, with one major +exception explained below. Instead, kobjects are used to control access to +a larger, domain-specific object. To this end, kobjects will be found +embedded in other structures. If you are used to thinking of things in +object-oriented terms, kobjects can be seen as a top-level, abstract class +from which other classes are derived. A kobject implements a set of +capabilities which are not particularly useful by themselves, but are +nice to have in other objects. The C language does not allow for the +direct expression of inheritance, so other techniques - such as structure +embedding - must be used. + +(As an aside, for those familiar with the kernel linked list implementation, +this is analogous as to how "list_head" structs are rarely useful on +their own, but are invariably found embedded in the larger objects of +interest.) + +So, for example, the UIO code in ``drivers/uio/uio.c`` has a structure that +defines the memory region associated with a uio device:: + + struct uio_map { + struct kobject kobj; + struct uio_mem *mem; + }; + +If you have a struct uio_map structure, finding its embedded kobject is +just a matter of using the kobj member. Code that works with kobjects will +often have the opposite problem, however: given a struct kobject pointer, +what is the pointer to the containing structure? You must avoid tricks +(such as assuming that the kobject is at the beginning of the structure) +and, instead, use the container_of() macro, found in ````:: + + container_of(ptr, type, member) + +where: + + * ``ptr`` is the pointer to the embedded kobject, + * ``type`` is the type of the containing structure, and + * ``member`` is the name of the structure field to which ``pointer`` points. + +The return value from container_of() is a pointer to the corresponding +container type. So, for example, a pointer ``kp`` to a struct kobject +embedded **within** a struct uio_map could be converted to a pointer to the +**containing** uio_map structure with:: + + struct uio_map *u_map = container_of(kp, struct uio_map, kobj); + +For convenience, programmers often define a simple macro for **back-casting** +kobject pointers to the containing type. Exactly this happens in the +earlier ``drivers/uio/uio.c``, as you can see here:: + + struct uio_map { + struct kobject kobj; + struct uio_mem *mem; + }; + + #define to_map(map) container_of(map, struct uio_map, kobj) + +where the macro argument "map" is a pointer to the struct kobject in +question. That macro is subsequently invoked with:: + + struct uio_map *map = to_map(kobj); + + +Initialization of kobjects +========================== + +Code which creates a kobject must, of course, initialize that object. Some +of the internal fields are setup with a (mandatory) call to kobject_init():: + + void kobject_init(struct kobject *kobj, const struct kobj_type *ktype); + +The ktype is required for a kobject to be created properly, as every kobject +must have an associated kobj_type. After calling kobject_init(), to +register the kobject with sysfs, the function kobject_add() must be called:: + + int kobject_add(struct kobject *kobj, struct kobject *parent, + const char *fmt, ...); + +This sets up the parent of the kobject and the name for the kobject +properly. If the kobject is to be associated with a specific kset, +kobj->kset must be assigned before calling kobject_add(). If a kset is +associated with a kobject, then the parent for the kobject can be set to +NULL in the call to kobject_add() and then the kobject's parent will be the +kset itself. + +As the name of the kobject is set when it is added to the kernel, the name +of the kobject should never be manipulated directly. If you must change +the name of the kobject, call kobject_rename():: + + int kobject_rename(struct kobject *kobj, const char *new_name); + +kobject_rename() does not perform any locking or have a solid notion of +what names are valid so the caller must provide their own sanity checking +and serialization. + +There is a function called kobject_set_name() but that is legacy cruft and +is being removed. If your code needs to call this function, it is +incorrect and needs to be fixed. + +To properly access the name of the kobject, use the function +kobject_name():: + + const char *kobject_name(const struct kobject * kobj); + +There is a helper function to both initialize and add the kobject to the +kernel at the same time, called surprisingly enough kobject_init_and_add():: + + int kobject_init_and_add(struct kobject *kobj, const struct kobj_type *ktype, + struct kobject *parent, const char *fmt, ...); + +The arguments are the same as the individual kobject_init() and +kobject_add() functions described above. + + +Uevents +======= + +After a kobject has been registered with the kobject core, you need to +announce to the world that it has been created. This can be done with a +call to kobject_uevent():: + + int kobject_uevent(struct kobject *kobj, enum kobject_action action); + +Use the **KOBJ_ADD** action for when the kobject is first added to the kernel. +This should be done only after any attributes or children of the kobject +have been initialized properly, as userspace will instantly start to look +for them when this call happens. + +When the kobject is removed from the kernel (details on how to do that are +below), the uevent for **KOBJ_REMOVE** will be automatically created by the +kobject core, so the caller does not have to worry about doing that by +hand. + + +Reference counts +================ + +One of the key functions of a kobject is to serve as a reference counter +for the object in which it is embedded. As long as references to the object +exist, the object (and the code which supports it) must continue to exist. +The low-level functions for manipulating a kobject's reference counts are:: + + struct kobject *kobject_get(struct kobject *kobj); + void kobject_put(struct kobject *kobj); + +A successful call to kobject_get() will increment the kobject's reference +counter and return the pointer to the kobject. + +When a reference is released, the call to kobject_put() will decrement the +reference count and, possibly, free the object. Note that kobject_init() +sets the reference count to one, so the code which sets up the kobject will +need to do a kobject_put() eventually to release that reference. + +Because kobjects are dynamic, they must not be declared statically or on +the stack, but instead, always allocated dynamically. Future versions of +the kernel will contain a run-time check for kobjects that are created +statically and will warn the developer of this improper usage. + +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. For more information on how to use struct kref, please see the +file Documentation/core-api/kref.rst in the Linux kernel source tree. + + +Creating "simple" kobjects +========================== + +Sometimes all that a developer wants is a way to create a simple directory +in the sysfs hierarchy, and not have to mess with the whole complication of +ksets, show and store functions, and other details. This is the one +exception where a single kobject should be created. To create such an +entry, use the function:: + + struct kobject *kobject_create_and_add(const char *name, struct kobject *parent); + +This function will create a kobject and place it in sysfs in the location +underneath the specified parent kobject. To create simple attributes +associated with this kobject, use:: + + int sysfs_create_file(struct kobject *kobj, const struct attribute *attr); + +or:: + + int sysfs_create_group(struct kobject *kobj, const struct attribute_group *grp); + +Both types of attributes used here, with a kobject that has been created +with the kobject_create_and_add(), can be of type kobj_attribute, so no +special custom attribute is needed to be created. + +See the example module, ``samples/kobject/kobject-example.c`` for an +implementation of a simple kobject and attributes. + + + +ktypes and release methods +========================== + +One important thing still missing from the discussion is what happens to a +kobject when its reference count reaches zero. The code which created the +kobject generally does not know when that will happen; if it did, there +would be little point in using a kobject in the first place. Even +predictable object lifecycles become more complicated when sysfs is brought +in as other portions of the kernel can get a reference on any kobject that +is registered in the system. + +The end result is that a structure protected by a kobject cannot be freed +before its reference count goes to zero. The reference count is not under +the direct control of the code which created the kobject. So that code must +be notified asynchronously whenever the last reference to one of its +kobjects goes away. + +Once you registered your kobject via kobject_add(), you must never use +kfree() to free it directly. The only safe way is to use kobject_put(). It +is good practice to always use kobject_put() after kobject_init() to avoid +errors creeping in. + +This notification is done through a kobject's release() method. Usually +such a method has a form like:: + + void my_object_release(struct kobject *kobj) + { + struct my_object *mine = container_of(kobj, struct my_object, kobj); + + /* Perform any additional cleanup on this object, then... */ + kfree(mine); + } + +One important point cannot be overstated: every kobject must have a +release() method, and the kobject must persist (in a consistent state) +until that method is called. If these constraints are not met, the code is +flawed. Note that the kernel will warn you if you forget to provide a +release() method. Do not try to get rid of this warning by providing an +"empty" release function. + +If all your cleanup function needs to do is call kfree(), then you must +create a wrapper function which uses container_of() to upcast to the correct +type (as shown in the example above) and then calls kfree() on the overall +structure. + +Note, the name of the kobject is available in the release function, but it +must NOT be changed within this callback. Otherwise there will be a memory +leak in the kobject core, which makes people unhappy. + +Interestingly, the release() method is not stored in the kobject itself; +instead, it is associated with the ktype. So let us introduce struct +kobj_type:: + + struct kobj_type { + void (*release)(struct kobject *kobj); + const struct sysfs_ops *sysfs_ops; + const struct attribute_group **default_groups; + const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj); + const void *(*namespace)(struct kobject *kobj); + void (*get_ownership)(struct kobject *kobj, kuid_t *uid, kgid_t *gid); + }; + +This structure is used to describe a particular type of kobject (or, more +correctly, of containing object). Every kobject needs to have an associated +kobj_type structure; a pointer to that structure must be specified when you +call kobject_init() or kobject_init_and_add(). + +The release field in struct kobj_type is, of course, a pointer to the +release() method for this type of kobject. The other two fields (sysfs_ops +and default_groups) control how objects of this type are represented in +sysfs; they are beyond the scope of this document. + +The default_groups pointer is a list of default attributes that will be +automatically created for any kobject that is registered with this ktype. + + +ksets +===== + +A kset is merely a collection of kobjects that want to be associated with +each other. There is no restriction that they be of the same ktype, but be +very careful if they are not. + +A kset serves these functions: + + - It serves as a bag containing a group of objects. A kset can be used by + the kernel to track "all block devices" or "all PCI device drivers." + + - A kset is also a subdirectory in sysfs, where the associated kobjects + with the kset can show up. Every kset contains a kobject which can be + set up to be the parent of other kobjects; the top-level directories of + the sysfs hierarchy are constructed in this way. + + - Ksets can support the "hotplugging" of kobjects and influence how + uevent events are reported to user space. + +In object-oriented terms, "kset" is the top-level container class; ksets +contain their own kobject, but that kobject is managed by the kset code and +should not be manipulated by any other user. + +A kset keeps its children in a standard kernel linked list. Kobjects point +back to their containing kset via their kset field. In almost all cases, +the kobjects belonging to a kset have that kset (or, strictly, its embedded +kobject) in their parent. + +As a kset contains a kobject within it, it should always be dynamically +created and never declared statically or on the stack. To create a new +kset use:: + + struct kset *kset_create_and_add(const char *name, + const struct kset_uevent_ops *uevent_ops, + struct kobject *parent_kobj); + +When you are finished with the kset, call:: + + void kset_unregister(struct kset *k); + +to destroy it. This removes the kset from sysfs and decrements its reference +count. When the reference count goes to zero, the kset will be released. +Because other references to the kset may still exist, the release may happen +after kset_unregister() returns. + +An example of using a kset can be seen in the +``samples/kobject/kset-example.c`` file in the kernel tree. + +If a kset wishes to control the uevent operations of the kobjects +associated with it, it can use the struct kset_uevent_ops to handle it:: + + struct kset_uevent_ops { + int (* const filter)(struct kobject *kobj); + const char *(* const name)(struct kobject *kobj); + int (* const uevent)(struct kobject *kobj, struct kobj_uevent_env *env); + }; + + +The filter function allows a kset to prevent a uevent from being emitted to +userspace for a specific kobject. If the function returns 0, the uevent +will not be emitted. + +The name function will be called to override the default name of the kset +that the uevent sends to userspace. By default, the name will be the same +as the kset itself, but this function, if present, can override that name. + +The uevent function will be called when the uevent is about to be sent to +userspace to allow more environment variables to be added to the uevent. + +One might ask how, exactly, a kobject is added to a kset, given that no +functions which perform that function have been presented. The answer is +that this task is handled by kobject_add(). When a kobject is passed to +kobject_add(), its kset member should point to the kset to which the +kobject will belong. kobject_add() will handle the rest. + +If the kobject belonging to a kset has no parent kobject set, it will be +added to the kset's directory. Not all members of a kset do necessarily +live in the kset directory. If an explicit parent kobject is assigned +before the kobject is added, the kobject is registered with the kset, but +added below the parent kobject. + + +Kobject removal +=============== + +After a kobject has been registered with the kobject core successfully, it +must be cleaned up when the code is finished with it. To do that, call +kobject_put(). By doing this, the kobject core will automatically clean up +all of the memory allocated by this kobject. If a ``KOBJ_ADD`` uevent has been +sent for the object, a corresponding ``KOBJ_REMOVE`` uevent will be sent, and +any other sysfs housekeeping will be handled for the caller properly. + +If you need to do a two-stage delete of the kobject (say you are not +allowed to sleep when you need to destroy the object), then call +kobject_del() which will unregister the kobject from sysfs. This makes the +kobject "invisible", but it is not cleaned up, and the reference count of +the object is still the same. At a later time call kobject_put() to finish +the cleanup of the memory associated with the kobject. + +kobject_del() can be used to drop the reference to the parent object, if +circular references are constructed. It is valid in some cases, that a +parent objects references a child. Circular references _must_ be broken +with an explicit call to kobject_del(), so that a release functions will be +called, and the objects in the former circle release each other. + + +Example code to copy from +========================= + +For a more complete example of using ksets and kobjects properly, see the +example programs ``samples/kobject/{kobject-example.c,kset-example.c}``, +which will be built as loadable modules if you select ``CONFIG_SAMPLE_KOBJECT``. -- cgit v1.2.3