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@@ -0,0 +1,263 @@
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+/*
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+ * Copyright (C) 2004-2005 IBM Corp. All Rights Reserved.
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+ * Copyright (C) 2006-2009 NEC Corporation.
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+ *
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+ * dm-queue-length.c
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+ *
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+ * Module Author: Stefan Bader, IBM
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+ * Modified by: Kiyoshi Ueda, NEC
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+ *
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+ * This file is released under the GPL.
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+ *
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+ * queue-length path selector - choose a path with the least number of
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+ * in-flight I/Os.
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+ */
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+
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+#include "dm.h"
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+#include "dm-path-selector.h"
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+
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+#include <linux/slab.h>
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+#include <linux/ctype.h>
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+#include <linux/errno.h>
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+#include <linux/module.h>
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+#include <asm/atomic.h>
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+
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+#define DM_MSG_PREFIX "multipath queue-length"
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+#define QL_MIN_IO 128
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+#define QL_VERSION "0.1.0"
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+
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+struct selector {
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+ struct list_head valid_paths;
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+ struct list_head failed_paths;
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+};
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+
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+struct path_info {
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+ struct list_head list;
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+ struct dm_path *path;
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+ unsigned repeat_count;
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+ atomic_t qlen; /* the number of in-flight I/Os */
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+};
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+
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+static struct selector *alloc_selector(void)
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+{
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+ struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
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+
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+ if (s) {
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+ INIT_LIST_HEAD(&s->valid_paths);
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+ INIT_LIST_HEAD(&s->failed_paths);
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+ }
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+
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+ return s;
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+}
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+
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+static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
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+{
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+ struct selector *s = alloc_selector();
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+
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+ if (!s)
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+ return -ENOMEM;
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+
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+ ps->context = s;
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+ return 0;
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+}
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+
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+static void ql_free_paths(struct list_head *paths)
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+{
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+ struct path_info *pi, *next;
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+
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+ list_for_each_entry_safe(pi, next, paths, list) {
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+ list_del(&pi->list);
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+ kfree(pi);
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+ }
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+}
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+
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+static void ql_destroy(struct path_selector *ps)
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+{
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+ struct selector *s = ps->context;
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+
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+ ql_free_paths(&s->valid_paths);
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+ ql_free_paths(&s->failed_paths);
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+ kfree(s);
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+ ps->context = NULL;
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+}
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+
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+static int ql_status(struct path_selector *ps, struct dm_path *path,
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+ status_type_t type, char *result, unsigned maxlen)
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+{
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+ unsigned sz = 0;
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+ struct path_info *pi;
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+
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+ /* When called with NULL path, return selector status/args. */
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+ if (!path)
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+ DMEMIT("0 ");
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+ else {
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+ pi = path->pscontext;
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+
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+ switch (type) {
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+ case STATUSTYPE_INFO:
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+ DMEMIT("%d ", atomic_read(&pi->qlen));
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+ break;
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+ case STATUSTYPE_TABLE:
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+ DMEMIT("%u ", pi->repeat_count);
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+ break;
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+ }
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+ }
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+
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+ return sz;
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+}
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+
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+static int ql_add_path(struct path_selector *ps, struct dm_path *path,
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+ int argc, char **argv, char **error)
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+{
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+ struct selector *s = ps->context;
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+ struct path_info *pi;
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+ unsigned repeat_count = QL_MIN_IO;
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+
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+ /*
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+ * Arguments: [<repeat_count>]
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+ * <repeat_count>: The number of I/Os before switching path.
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+ * If not given, default (QL_MIN_IO) is used.
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+ */
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+ if (argc > 1) {
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+ *error = "queue-length ps: incorrect number of arguments";
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+ return -EINVAL;
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+ }
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+
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+ if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
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+ *error = "queue-length ps: invalid repeat count";
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+ return -EINVAL;
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+ }
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+
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+ /* Allocate the path information structure */
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+ pi = kmalloc(sizeof(*pi), GFP_KERNEL);
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+ if (!pi) {
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+ *error = "queue-length ps: Error allocating path information";
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+ return -ENOMEM;
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+ }
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+
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+ pi->path = path;
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+ pi->repeat_count = repeat_count;
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+ atomic_set(&pi->qlen, 0);
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+
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+ path->pscontext = pi;
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+
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+ list_add_tail(&pi->list, &s->valid_paths);
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+
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+ return 0;
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+}
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+
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+static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
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+{
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+ struct selector *s = ps->context;
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+ struct path_info *pi = path->pscontext;
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+
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+ list_move(&pi->list, &s->failed_paths);
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+}
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+
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+static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
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+{
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+ struct selector *s = ps->context;
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+ struct path_info *pi = path->pscontext;
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+
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+ list_move_tail(&pi->list, &s->valid_paths);
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+
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+ return 0;
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+}
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+
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+/*
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+ * Select a path having the minimum number of in-flight I/Os
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+ */
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+static struct dm_path *ql_select_path(struct path_selector *ps,
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+ unsigned *repeat_count, size_t nr_bytes)
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+{
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+ struct selector *s = ps->context;
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+ struct path_info *pi = NULL, *best = NULL;
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+
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+ if (list_empty(&s->valid_paths))
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+ return NULL;
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+
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+ /* Change preferred (first in list) path to evenly balance. */
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+ list_move_tail(s->valid_paths.next, &s->valid_paths);
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+
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+ list_for_each_entry(pi, &s->valid_paths, list) {
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+ if (!best ||
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+ (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
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+ best = pi;
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+
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+ if (!atomic_read(&best->qlen))
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+ break;
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+ }
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+
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+ if (!best)
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+ return NULL;
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+
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+ *repeat_count = best->repeat_count;
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+
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+ return best->path;
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+}
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+
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+static int ql_start_io(struct path_selector *ps, struct dm_path *path,
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+ size_t nr_bytes)
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+{
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+ struct path_info *pi = path->pscontext;
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+
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+ atomic_inc(&pi->qlen);
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+
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+ return 0;
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+}
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+
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+static int ql_end_io(struct path_selector *ps, struct dm_path *path,
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+ size_t nr_bytes)
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+{
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+ struct path_info *pi = path->pscontext;
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+
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+ atomic_dec(&pi->qlen);
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+
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+ return 0;
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+}
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+
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+static struct path_selector_type ql_ps = {
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+ .name = "queue-length",
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+ .module = THIS_MODULE,
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+ .table_args = 1,
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+ .info_args = 1,
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+ .create = ql_create,
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+ .destroy = ql_destroy,
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+ .status = ql_status,
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+ .add_path = ql_add_path,
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+ .fail_path = ql_fail_path,
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+ .reinstate_path = ql_reinstate_path,
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+ .select_path = ql_select_path,
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+ .start_io = ql_start_io,
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+ .end_io = ql_end_io,
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+};
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+
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+static int __init dm_ql_init(void)
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+{
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+ int r = dm_register_path_selector(&ql_ps);
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+
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+ if (r < 0)
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+ DMERR("register failed %d", r);
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+
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+ DMINFO("version " QL_VERSION " loaded");
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+
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+ return r;
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+}
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+
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+static void __exit dm_ql_exit(void)
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+{
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+ int r = dm_unregister_path_selector(&ql_ps);
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+
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+ if (r < 0)
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+ DMERR("unregister failed %d", r);
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+}
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+
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+module_init(dm_ql_init);
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+module_exit(dm_ql_exit);
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+
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+MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
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+MODULE_DESCRIPTION(
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+ "(C) Copyright IBM Corp. 2004,2005 All Rights Reserved.\n"
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+ DM_NAME " path selector to balance the number of in-flight I/Os"
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+);
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+MODULE_LICENSE("GPL");
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