[SCSI] scsi_dh: create lookup cache

Create a cache of devices that are seen in a system. This will avoid
the unnecessary traversal of the device list in the scsi_dh when there
are multiple luns of a same type.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 105 insertions, 24 deletions

diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
index a9159681ff27..a518f2eff19a 100644
--- a/drivers/scsi/device_handler/scsi_dh.c
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -24,8 +24,16 @@
 #include <scsi/scsi_dh.h>
 #include "../scsi_priv.h"
 
+struct scsi_dh_devinfo_list {
+        struct list_head node;
+        char vendor[9];
+        char model[17];
+        struct scsi_device_handler *handler;
+};
+
 static DEFINE_SPINLOCK(list_lock);
 static LIST_HEAD(scsi_dh_list);
+static LIST_HEAD(scsi_dh_dev_list);
 
 static struct scsi_device_handler *get_device_handler(const char *name)
 {
@@ -42,21 +50,94 @@ static struct scsi_device_handler *get_device_handler(const char *name)
         return found;
 }
 
-static int device_handler_match(struct scsi_device_handler *tmp,
-                                struct scsi_device *sdev)
+
+static struct scsi_device_handler *
+scsi_dh_cache_lookup(struct scsi_device *sdev)
 {
-        int i;
-
-        for(i = 0; tmp->devlist[i].vendor; i++) {
-                if (!strncmp(sdev->vendor, tmp->devlist[i].vendor,
-                             strlen(tmp->devlist[i].vendor)) &&
-                    !strncmp(sdev->model, tmp->devlist[i].model,
-                             strlen(tmp->devlist[i].model))) {
-                        return 1;
+        struct scsi_dh_devinfo_list *tmp;
+        struct scsi_device_handler *found_dh = NULL;
+
+        spin_lock(&list_lock);
+        list_for_each_entry(tmp, &scsi_dh_dev_list, node) {
+                if (!strncmp(sdev->vendor, tmp->vendor, strlen(tmp->vendor)) &&
+                    !strncmp(sdev->model, tmp->model, strlen(tmp->model))) {
+                        found_dh = tmp->handler;
+                        break;
                 }
         }
+        spin_unlock(&list_lock);
 
-        return 0;
+        return found_dh;
+}
+
+static int scsi_dh_handler_lookup(struct scsi_device_handler *scsi_dh,
+                                  struct scsi_device *sdev)
+{
+        int i, found = 0;
+
+        for(i = 0; scsi_dh->devlist[i].vendor; i++) {
+                if (!strncmp(sdev->vendor, scsi_dh->devlist[i].vendor,
+                             strlen(scsi_dh->devlist[i].vendor)) &&
+                    !strncmp(sdev->model, scsi_dh->devlist[i].model,
+                             strlen(scsi_dh->devlist[i].model))) {
+                        found = 1;
+                        break;
+                }
+        }
+        return found;
+}
+
+/*
+ * device_handler_match - Attach a device handler to a device
+ * @scsi_dh - The device handler to match against or NULL
+ * @sdev - SCSI device to be tested against @scsi_dh
+ *
+ * Tests @sdev against the device handler @scsi_dh or against
+ * all registered device_handler if @scsi_dh == NULL.
+ * Returns the found device handler or NULL if not found.
+ */
+static struct scsi_device_handler *
+device_handler_match(struct scsi_device_handler *scsi_dh,
+                     struct scsi_device *sdev)
+{
+        struct scsi_device_handler *found_dh = NULL;
+        struct scsi_dh_devinfo_list *tmp;
+
+        found_dh = scsi_dh_cache_lookup(sdev);
+        if (found_dh)
+                return found_dh;
+
+        if (scsi_dh) {
+                if (scsi_dh_handler_lookup(scsi_dh, sdev))
+                        found_dh = scsi_dh;
+        } else {
+                struct scsi_device_handler *tmp_dh;
+
+                spin_lock(&list_lock);
+                list_for_each_entry(tmp_dh, &scsi_dh_list, list) {
+                        if (scsi_dh_handler_lookup(tmp_dh, sdev))
+                                found_dh = tmp_dh;
+                }
+                spin_unlock(&list_lock);
+        }
+
+        if (found_dh) { /* If device is found, add it to the cache */
+                tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
+                if (tmp) {
+                        strncpy(tmp->vendor, sdev->vendor, 8);
+                        strncpy(tmp->model, sdev->model, 16);
+                        tmp->vendor[8] = '\0';
+                        tmp->model[16] = '\0';
+                        tmp->handler = found_dh;
+                        spin_lock(&list_lock);
+                        list_add(&tmp->node, &scsi_dh_dev_list);
+                        spin_unlock(&list_lock);
+                } else {
+                        found_dh = NULL;
+                }
+        }
+
+        return found_dh;
 }
 
 /*
@@ -203,26 +284,18 @@ static int scsi_dh_notifier(struct notifier_block *nb,
         struct device *dev = data;
         struct scsi_device *sdev;
         int err = 0;
-        struct scsi_device_handler *tmp, *devinfo = NULL;
+        struct scsi_device_handler *devinfo = NULL;
 
         if (!scsi_is_sdev_device(dev))
                 return 0;
 
         sdev = to_scsi_device(dev);
 
-        spin_lock(&list_lock);
-        list_for_each_entry(tmp, &scsi_dh_list, list) {
-                if (device_handler_match(tmp, sdev)) {
-                        devinfo = tmp;
-                        break;
-                }
-        }
-        spin_unlock(&list_lock);
-
-        if (!devinfo)
-                goto out;
-
         if (action == BUS_NOTIFY_ADD_DEVICE) {
+                devinfo = device_handler_match(NULL, sdev);
+                if (!devinfo)
+                        goto out;
+
                 err = scsi_dh_handler_attach(sdev, devinfo);
                 if (!err)
                         err = device_create_file(dev, &scsi_dh_state_attr);
@@ -312,6 +385,8 @@ EXPORT_SYMBOL_GPL(scsi_register_device_handler);
  */
 int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh)
 {
+        struct scsi_dh_devinfo_list *tmp, *pos;
+
         if (!get_device_handler(scsi_dh->name))
                 return -ENODEV;
 
@@ -320,6 +395,12 @@ int scsi_unregister_device_handler(struct scsi_device_handler *scsi_dh)
 
         spin_lock(&list_lock);
         list_del(&scsi_dh->list);
+        list_for_each_entry_safe(pos, tmp, &scsi_dh_dev_list, node) {
+                if (pos->handler == scsi_dh) {
+                        list_del(&pos->node);
+                        kfree(pos);
+                }
+        }
         spin_unlock(&list_lock);
         printk(KERN_INFO "%s: device handler unregistered\n", scsi_dh->name);