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);