--- /dev/null
+#ifndef _BACKPORTS_LINUX_STATIC_KEY_H
+#define _BACKPORTS_LINUX_STATIC_KEY_H 1
+
+#include <linux/version.h>
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,3,0) /* kernels >= 3.3 */
+/*
+ * XXX: NOTE!
+ *
+ * Some 3.3 kernels carry <linux/static.h> but some don't even though its
+ * its including <linux/jump_label.h>. What makes it more confusing is that
+ * later all this got shuffled. The safe thing to do then is to just assume
+ * kernels 3.3..3.4 don't have it and include <linux/jump_label.h> instead,
+ * and for newer kernels include <linux/static_key.h>.
+ */
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,5,0)
+#include_next <linux/static_key.h>
+#else
+#include <linux/jump_label.h>
+#endif
+
+#else /* kernels < 3.3 */
+/*
+ * in between 2.6.37 - 3.5 there's a slew of changes that make
+ * it hard to backport this properly. If you are interested in
+ * trying you can use this as reference:
+ *
+ * http://drvbp1.linux-foundation.org/~mcgrof/examples/2014/04/01/backport-static-keys.patch
+ *
+ * And these notes:
+ *
+ * < v2.6.37 - No tracing support
+ * bf5438fc - v2.6.37 - Jump label support added primarily for tracing but
+ * tracing was broken, later kernels started sporting
+ * functional tracing.
+ * d430d3d7e - v3.0 - Static branch optimizations for jump labels
+ * c5905afb - v3.3 - Static keys split out, note on the below issue
+ * c5905afb - v3.5 - git describe --contains c5905afb claims but not true!
+ * c4b2c0c5f - v3.13 - Adds static_key_initialized(), STATIC_KEY_CHECK_USE()
+ *
+ * Because all of this we skip 2.6.37 - 3.3 but and adding support for older
+ * can be done by of carrying over the non-architecture optimized code.
+ * Carrying new changes into this file is a burden though so if we really
+ * find use for this we could just split the non optimized versions upstream
+ * and copy that through an automatic process.
+ */
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,37)
+/*
+ * For kernels older than 2.6.37 we just take on the
+ * implementation in the kernel that assumes you have
+ * either no toolchain or architecture kernel support
+ * for the jump labels. Daring folks who wish to embark
+ * on a nutty journey may wish to see if they can backport
+ * architectural specific changes here.
+ *
+ * Jump label support was added via commit
+ * bf5438fca2950b03c21ad868090cc1a8fcd49536 through kernel
+ * v2.6.37-rc1~214^2~33^2~8
+ */
+
+/*
+ * Jump label support
+ *
+ * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
+ * Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Jump labels provide an interface to generate dynamic branches using
+ * self-modifying code. Assuming toolchain and architecture support the result
+ * of a "if (static_key_false(&key))" statement is a unconditional branch (which
+ * defaults to false - and the true block is placed out of line).
+ *
+ * However at runtime we can change the branch target using
+ * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key
+ * object and for as long as there are references all branches referring to
+ * that particular key will point to the (out of line) true block.
+ *
+ * Since this relies on modifying code the static_key_slow_{inc,dec}() functions
+ * must be considered absolute slow paths (machine wide synchronization etc.).
+ * OTOH, since the affected branches are unconditional their runtime overhead
+ * will be absolutely minimal, esp. in the default (off) case where the total
+ * effect is a single NOP of appropriate size. The on case will patch in a jump
+ * to the out-of-line block.
+ *
+ * When the control is directly exposed to userspace it is prudent to delay the
+ * decrement to avoid high frequency code modifications which can (and do)
+ * cause significant performance degradation. Struct static_key_deferred and
+ * static_key_slow_dec_deferred() provide for this.
+ *
+ * Lacking toolchain and or architecture support, it falls back to a simple
+ * conditional branch.
+ *
+ * struct static_key my_key = STATIC_KEY_INIT_TRUE;
+ *
+ * if (static_key_true(&my_key)) {
+ * }
+ *
+ * will result in the true case being in-line and starts the key with a single
+ * reference. Mixing static_key_true() and static_key_false() on the same key is not
+ * allowed.
+ *
+ * Not initializing the key (static data is initialized to 0s anyway) is the
+ * same as using STATIC_KEY_INIT_FALSE.
+ *
+*/
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <linux/bug.h>
+
+/*
+ * For the backport we leave out static_key_initialized as
+ * no architecture code is provided to support jump labels, so
+ * we treat jump labels as simply atomic values which drive
+ * branches. Since we don't backport static_key_initialized
+ * we leave out all STATIC_KEY_CHECK_USE() uses.
+ */
+
+enum jump_label_type {
+ JUMP_LABEL_DISABLE = 0,
+ JUMP_LABEL_ENABLE,
+};
+
+struct module;
+
+#include <linux/atomic.h>
+
+struct static_key {
+ atomic_t enabled;
+};
+
+static __always_inline bool static_key_false(struct static_key *key)
+{
+ if (unlikely(atomic_read(&key->enabled) > 0))
+ return true;
+ return false;
+}
+
+static __always_inline bool static_key_true(struct static_key *key)
+{
+ if (likely(atomic_read(&key->enabled) > 0))
+ return true;
+ return false;
+}
+
+static inline void static_key_slow_inc(struct static_key *key)
+{
+ atomic_inc(&key->enabled);
+}
+
+static inline void static_key_slow_dec(struct static_key *key)
+{
+ atomic_dec(&key->enabled);
+}
+
+static inline int jump_label_text_reserved(void *start, void *end)
+{
+ return 0;
+}
+
+static inline void jump_label_lock(void) {}
+static inline void jump_label_unlock(void) {}
+
+static inline int jump_label_apply_nops(struct module *mod)
+{
+ return 0;
+}
+
+#define STATIC_KEY_INIT_TRUE ((struct static_key) \
+ { .enabled = ATOMIC_INIT(1) })
+#define STATIC_KEY_INIT_FALSE ((struct static_key) \
+ { .enabled = ATOMIC_INIT(0) })
+
+
+#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
+#define jump_label_enabled static_key_enabled
+
+static inline bool static_key_enabled(struct static_key *key)
+{
+ return (atomic_read(&key->enabled) > 0);
+}
+
+#endif /* kernels older than 2.6.37 */
+#endif /* kernels < 3.3 */
+
+#endif /* _BACKPORTS_LINUX_STATIC_KEY_H */
projects / openwrt / staging / blogic.git / commitdiff