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authorLinus Torvalds <torvalds@linux-foundation.org>2014-01-20 15:49:44 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-20 15:49:44 -0800
commitd3bad75a6d57416cf7478ca2a1e42f699bc17ec5 (patch)
treed79e9403e17aef5fee028fc550eec583dda38e0c /Documentation
parent9f67627a0fea99b080a190d2d24cc1e2634aa2f7 (diff)
parentdb4aad209bc9aefd91f0a9aeb9e37364088b39ad (diff)
downloadlinux-stericsson-d3bad75a6d57416cf7478ca2a1e42f699bc17ec5.tar.gz
Merge tag 'driver-core-3.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
Pull driver core / sysfs patches from Greg KH: "Here's the big driver core and sysfs patch set for 3.14-rc1. There's a lot of work here moving sysfs logic out into a "kernfs" to allow other subsystems to also have a virtual filesystem with the same attributes of sysfs (handle device disconnect, dynamic creation / removal as needed / unneeded, etc) This is primarily being done for the cgroups filesystem, but the goal is to also move debugfs to it when it is ready, solving all of the known issues in that filesystem as well. The code isn't completed yet, but all should be stable now (there is a big section that was reverted due to problems found when testing) There's also some other smaller fixes, and a driver core addition that allows for a "collection" of objects, that the DRM people will be using soon (it's in this tree to make merges after -rc1 easier) All of this has been in linux-next with no reported issues" * tag 'driver-core-3.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (113 commits) kernfs: associate a new kernfs_node with its parent on creation kernfs: add struct dentry declaration in kernfs.h kernfs: fix get_active failure handling in kernfs_seq_*() Revert "kernfs: fix get_active failure handling in kernfs_seq_*()" Revert "kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq" Revert "kernfs: remove KERNFS_ACTIVE_REF and add kernfs_lockdep()" Revert "kernfs: remove KERNFS_REMOVED" Revert "kernfs: restructure removal path to fix possible premature return" Revert "kernfs: invoke kernfs_unmap_bin_file() directly from __kernfs_remove()" Revert "kernfs: remove kernfs_addrm_cxt" Revert "kernfs: make kernfs_get_active() block if the node is deactivated but not removed" Revert "kernfs: implement kernfs_{de|re}activate[_self]()" Revert "kernfs, sysfs, driver-core: implement kernfs_remove_self() and its wrappers" Revert "pci: use device_remove_file_self() instead of device_schedule_callback()" Revert "scsi: use device_remove_file_self() instead of device_schedule_callback()" Revert "s390: use device_remove_file_self() instead of device_schedule_callback()" Revert "sysfs, driver-core: remove unused {sysfs|device}_schedule_callback_owner()" Revert "kernfs: remove unnecessary NULL check in __kernfs_remove()" kernfs: remove unnecessary NULL check in __kernfs_remove() drivers/base: provide an infrastructure for componentised subsystems ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/driver-model/design-patterns.txt116
-rw-r--r--Documentation/kobject.txt5
2 files changed, 120 insertions, 1 deletions
diff --git a/Documentation/driver-model/design-patterns.txt b/Documentation/driver-model/design-patterns.txt
new file mode 100644
index 000000000000..ba7b2df64904
--- /dev/null
+++ b/Documentation/driver-model/design-patterns.txt
@@ -0,0 +1,116 @@
+
+Device Driver Design Patterns
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This document describes a few common design patterns found in device drivers.
+It is likely that subsystem maintainers will ask driver developers to
+conform to these design patterns.
+
+1. State Container
+2. container_of()
+
+
+1. State Container
+~~~~~~~~~~~~~~~~~~
+
+While the kernel contains a few device drivers that assume that they will
+only be probed() once on a certain system (singletons), it is custom to assume
+that the device the driver binds to will appear in several instances. This
+means that the probe() function and all callbacks need to be reentrant.
+
+The most common way to achieve this is to use the state container design
+pattern. It usually has this form:
+
+struct foo {
+ spinlock_t lock; /* Example member */
+ (...)
+};
+
+static int foo_probe(...)
+{
+ struct foo *foo;
+
+ foo = devm_kzalloc(dev, sizeof(*foo), GFP_KERNEL);
+ if (!foo)
+ return -ENOMEM;
+ spin_lock_init(&foo->lock);
+ (...)
+}
+
+This will create an instance of struct foo in memory every time probe() is
+called. This is our state container for this instance of the device driver.
+Of course it is then necessary to always pass this instance of the
+state around to all functions that need access to the state and its members.
+
+For example, if the driver is registering an interrupt handler, you would
+pass around a pointer to struct foo like this:
+
+static irqreturn_t foo_handler(int irq, void *arg)
+{
+ struct foo *foo = arg;
+ (...)
+}
+
+static int foo_probe(...)
+{
+ struct foo *foo;
+
+ (...)
+ ret = request_irq(irq, foo_handler, 0, "foo", foo);
+}
+
+This way you always get a pointer back to the correct instance of foo in
+your interrupt handler.
+
+
+2. container_of()
+~~~~~~~~~~~~~~~~~
+
+Continuing on the above example we add an offloaded work:
+
+struct foo {
+ spinlock_t lock;
+ struct workqueue_struct *wq;
+ struct work_struct offload;
+ (...)
+};
+
+static void foo_work(struct work_struct *work)
+{
+ struct foo *foo = container_of(work, struct foo, offload);
+
+ (...)
+}
+
+static irqreturn_t foo_handler(int irq, void *arg)
+{
+ struct foo *foo = arg;
+
+ queue_work(foo->wq, &foo->offload);
+ (...)
+}
+
+static int foo_probe(...)
+{
+ struct foo *foo;
+
+ foo->wq = create_singlethread_workqueue("foo-wq");
+ INIT_WORK(&foo->offload, foo_work);
+ (...)
+}
+
+The design pattern is the same for an hrtimer or something similar that will
+return a single argument which is a pointer to a struct member in the
+callback.
+
+container_of() is a macro defined in <linux/kernel.h>
+
+What container_of() does is to obtain a pointer to the containing struct from
+a pointer to a member by a simple subtraction using the offsetof() macro from
+standard C, which allows something similar to object oriented behaviours.
+Notice that the contained member must not be a pointer, but an actual member
+for this to work.
+
+We can see here that we avoid having global pointers to our struct foo *
+instance this way, while still keeping the number of parameters passed to the
+work function to a single pointer.
diff --git a/Documentation/kobject.txt b/Documentation/kobject.txt
index c5182bb2c16c..f87241dfed87 100644
--- a/Documentation/kobject.txt
+++ b/Documentation/kobject.txt
@@ -342,7 +342,10 @@ kset use:
When you are finished with the kset, call:
void kset_unregister(struct kset *kset);
-to destroy it.
+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.