1 files changed, 194 insertions, 0 deletions
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
new file mode 100644
index 000000000000..6d1675508eb5
--- /dev/null
+++ b/block/blk-ioc.c
@@ -0,0 +1,194 @@
+/*
+ * Functions related to io context handling
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/bootmem.h>	/* for max_pfn/max_low_pfn */
+
+#include "blk.h"
+
+/*
+ * For io context allocations
+ */
+static struct kmem_cache *iocontext_cachep;
+
+static void cfq_dtor(struct io_context *ioc)
+{
+	struct cfq_io_context *cic[1];
+	int r;
+
+	/*
+	 * We don't have a specific key to lookup with, so use the gang
+	 * lookup to just retrieve the first item stored. The cfq exit
+	 * function will iterate the full tree, so any member will do.
+	 */
+	r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1);
+	if (r > 0)
+		cic[0]->dtor(ioc);
+}
+
+/*
+ * IO Context helper functions. put_io_context() returns 1 if there are no
+ * more users of this io context, 0 otherwise.
+ */
+int put_io_context(struct io_context *ioc)
+{
+	if (ioc == NULL)
+		return 1;
+
+	BUG_ON(atomic_read(&ioc->refcount) == 0);
+
+	if (atomic_dec_and_test(&ioc->refcount)) {
+		rcu_read_lock();
+		if (ioc->aic && ioc->aic->dtor)
+			ioc->aic->dtor(ioc->aic);
+		rcu_read_unlock();
+		cfq_dtor(ioc);
+
+		kmem_cache_free(iocontext_cachep, ioc);
+		return 1;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(put_io_context);
+
+static void cfq_exit(struct io_context *ioc)
+{
+	struct cfq_io_context *cic[1];
+	int r;
+
+	rcu_read_lock();
+	/*
+	 * See comment for cfq_dtor()
+	 */
+	r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1);
+	rcu_read_unlock();
+
+	if (r > 0)
+		cic[0]->exit(ioc);
+}
+
+/* Called by the exitting task */
+void exit_io_context(void)
+{
+	struct io_context *ioc;
+
+	task_lock(current);
+	ioc = current->io_context;
+	current->io_context = NULL;
+	task_unlock(current);
+
+	if (atomic_dec_and_test(&ioc->nr_tasks)) {
+		if (ioc->aic && ioc->aic->exit)
+			ioc->aic->exit(ioc->aic);
+		cfq_exit(ioc);
+
+		put_io_context(ioc);
+	}
+}
+
+struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
+{
+	struct io_context *ret;
+
+	ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
+	if (ret) {
+		atomic_set(&ret->refcount, 1);
+		atomic_set(&ret->nr_tasks, 1);
+		spin_lock_init(&ret->lock);
+		ret->ioprio_changed = 0;
+		ret->ioprio = 0;
+		ret->last_waited = jiffies; /* doesn't matter... */
+		ret->nr_batch_requests = 0; /* because this is 0 */
+		ret->aic = NULL;
+		INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
+		ret->ioc_data = NULL;
+	}
+
+	return ret;
+}
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * Otherwise, return its existing IO context.
+ *
+ * This returned IO context doesn't have a specifically elevated refcount,
+ * but since the current task itself holds a reference, the context can be
+ * used in general code, so long as it stays within `current` context.
+ */
+struct io_context *current_io_context(gfp_t gfp_flags, int node)
+{
+	struct task_struct *tsk = current;
+	struct io_context *ret;
+
+	ret = tsk->io_context;
+	if (likely(ret))
+		return ret;
+
+	ret = alloc_io_context(gfp_flags, node);
+	if (ret) {
+		/* make sure set_task_ioprio() sees the settings above */
+		smp_wmb();
+		tsk->io_context = ret;
+	}
+
+	return ret;
+}
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * If it does have a context, take a ref on it.
+ *
+ * This is always called in the context of the task which submitted the I/O.
+ */
+struct io_context *get_io_context(gfp_t gfp_flags, int node)
+{
+	struct io_context *ret = NULL;
+
+	/*
+	 * Check for unlikely race with exiting task. ioc ref count is
+	 * zero when ioc is being detached.
+	 */
+	do {
+		ret = current_io_context(gfp_flags, node);
+		if (unlikely(!ret))
+			break;
+	} while (!atomic_inc_not_zero(&ret->refcount));
+
+	return ret;
+}
+EXPORT_SYMBOL(get_io_context);
+
+void copy_io_context(struct io_context **pdst, struct io_context **psrc)
+{
+	struct io_context *src = *psrc;
+	struct io_context *dst = *pdst;
+
+	if (src) {
+		BUG_ON(atomic_read(&src->refcount) == 0);
+		atomic_inc(&src->refcount);
+		put_io_context(dst);
+		*pdst = src;
+	}
+}
+EXPORT_SYMBOL(copy_io_context);
+
+void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
+{
+	struct io_context *temp;
+	temp = *ioc1;
+	*ioc1 = *ioc2;
+	*ioc2 = temp;
+}
+EXPORT_SYMBOL(swap_io_context);
+
+int __init blk_ioc_init(void)
+{
+	iocontext_cachep = kmem_cache_create("blkdev_ioc",
+			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
+	return 0;
+}
+subsys_initcall(blk_ioc_init);