[SCSI] Add ability to scan scsi busses asynchronously

Since it often takes around 20-30 seconds to scan a scsi bus, it's
highly advantageous to do this in parallel with other things.  The bulk
of this patch is ensuring that devices don't change numbering, and that
all devices are discovered prior to trying to start init.  For those
who build SCSI as modules, there's a new scsi_wait_scan module that will
ensure all bus scans are finished.

This patch only handles drivers which call scsi_scan_host.  Fibre Channel,
SAS, SATA, USB and Firewire all need additional work.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 197 insertions, 6 deletions

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index fd9e281c3bfe..148e24cc3222 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -29,7 +29,9 @@
 #include <linux/moduleparam.h>
 #include <linux/init.h>
 #include <linux/blkdev.h>
-#include <asm/semaphore.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/spinlock.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
@@ -87,6 +89,11 @@ module_param_named(max_luns, max_scsi_luns, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(max_luns,
                  "last scsi LUN (should be between 1 and 2^32-1)");
 
+static char scsi_scan_type[6] = "sync";
+
+module_param_string(scan, scsi_scan_type, sizeof(scsi_scan_type), S_IRUGO);
+MODULE_PARM_DESC(scan, "sync, async or none");
+
 /*
  * max_scsi_report_luns: the maximum number of LUNS that will be
  * returned from the REPORT LUNS command. 8 times this value must
@@ -108,6 +115,68 @@ MODULE_PARM_DESC(inq_timeout,
                  "Timeout (in seconds) waiting for devices to answer INQUIRY."
                  " Default is 5. Some non-compliant devices need more.");
 
+static DEFINE_SPINLOCK(async_scan_lock);
+static LIST_HEAD(scanning_hosts);
+
+struct async_scan_data {
+        struct list_head list;
+        struct Scsi_Host *shost;
+        struct completion prev_finished;
+};
+
+/**
+ * scsi_complete_async_scans - Wait for asynchronous scans to complete
+ *
+ * Asynchronous scans add themselves to the scanning_hosts list.  Once
+ * that list is empty, we know that the scans are complete.  Rather than
+ * waking up periodically to check the state of the list, we pretend to be
+ * a scanning task by adding ourselves at the end of the list and going to
+ * sleep.  When the task before us wakes us up, we take ourselves off the
+ * list and return.
+ */
+int scsi_complete_async_scans(void)
+{
+        struct async_scan_data *data;
+
+        do {
+                if (list_empty(&scanning_hosts))
+                        return 0;
+                /* If we can't get memory immediately, that's OK.  Just
+                 * sleep a little.  Even if we never get memory, the async
+                 * scans will finish eventually.
+                 */
+                data = kmalloc(sizeof(*data), GFP_KERNEL);
+                if (!data)
+                        msleep(1);
+        } while (!data);
+
+        data->shost = NULL;
+        init_completion(&data->prev_finished);
+
+        spin_lock(&async_scan_lock);
+        /* Check that there's still somebody else on the list */
+        if (list_empty(&scanning_hosts))
+                goto done;
+        list_add_tail(&data->list, &scanning_hosts);
+        spin_unlock(&async_scan_lock);
+
+        printk(KERN_INFO "scsi: waiting for bus probes to complete ...\n");
+        wait_for_completion(&data->prev_finished);
+
+        spin_lock(&async_scan_lock);
+        list_del(&data->list);
+ done:
+        spin_unlock(&async_scan_lock);
+
+        kfree(data);
+        return 0;
+}
+
+#ifdef MODULE
+/* Only exported for the benefit of scsi_wait_scan */
+EXPORT_SYMBOL_GPL(scsi_complete_async_scans);
+#endif
+
 /**
  * scsi_unlock_floptical - unlock device via a special MODE SENSE command
  * @sdev:       scsi device to send command to
@@ -619,7 +688,7 @@ static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
  *     SCSI_SCAN_LUN_PRESENT: a new scsi_device was allocated and initialized
  **/
 static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
-                int *bflags)
+                int *bflags, int async)
 {
         /*
          * XXX do not save the inquiry, since it can change underneath us,
@@ -795,7 +864,7 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
          * register it and tell the rest of the kernel
          * about it.
          */
-        if (scsi_sysfs_add_sdev(sdev) != 0)
+        if (!async && scsi_sysfs_add_sdev(sdev) != 0)
                 return SCSI_SCAN_NO_RESPONSE;
 
         return SCSI_SCAN_LUN_PRESENT;
@@ -964,7 +1033,7 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
                 goto out_free_result;
         }
 
-        res = scsi_add_lun(sdev, result, &bflags);
+        res = scsi_add_lun(sdev, result, &bflags, shost->async_scan);
         if (res == SCSI_SCAN_LUN_PRESENT) {
                 if (bflags & BLIST_KEY) {
                         sdev->lockable = 0;
@@ -1464,6 +1533,9 @@ void scsi_scan_target(struct device *parent, unsigned int channel,
 {
         struct Scsi_Host *shost = dev_to_shost(parent);
 
+        if (!shost->async_scan)
+                scsi_complete_async_scans();
+
         mutex_lock(&shost->scan_mutex);
         if (scsi_host_scan_allowed(shost))
                 __scsi_scan_target(parent, channel, id, lun, rescan);
@@ -1509,6 +1581,9 @@ int scsi_scan_host_selected(struct Scsi_Host *shost, unsigned int channel,
                 "%s: <%u:%u:%u>\n",
                 __FUNCTION__, channel, id, lun));
 
+        if (!shost->async_scan)
+                scsi_complete_async_scans();
+
         if (((channel != SCAN_WILD_CARD) && (channel > shost->max_channel)) ||
             ((id != SCAN_WILD_CARD) && (id >= shost->max_id)) ||
             ((lun != SCAN_WILD_CARD) && (lun > shost->max_lun)))
@@ -1529,14 +1604,130 @@ int scsi_scan_host_selected(struct Scsi_Host *shost, unsigned int channel,
         return 0;
 }
 
+static void scsi_sysfs_add_devices(struct Scsi_Host *shost)
+{
+        struct scsi_device *sdev;
+        shost_for_each_device(sdev, shost) {
+                if (scsi_sysfs_add_sdev(sdev) != 0)
+                        scsi_destroy_sdev(sdev);
+        }
+}
+
+/**
+ * scsi_prep_async_scan - prepare for an async scan
+ * @shost: the host which will be scanned
+ * Returns: a cookie to be passed to scsi_finish_async_scan()
+ *
+ * Tells the midlayer this host is going to do an asynchronous scan.
+ * It reserves the host's position in the scanning list and ensures
+ * that other asynchronous scans started after this one won't affect the
+ * ordering of the discovered devices.
+ */
+struct async_scan_data *scsi_prep_async_scan(struct Scsi_Host *shost)
+{
+        struct async_scan_data *data;
+
+        if (strncmp(scsi_scan_type, "sync", 4) == 0)
+                return NULL;
+
+        if (shost->async_scan) {
+                printk("%s called twice for host %d", __FUNCTION__,
+                                shost->host_no);
+                dump_stack();
+                return NULL;
+        }
+
+        data = kmalloc(sizeof(*data), GFP_KERNEL);
+        if (!data)
+                goto err;
+        data->shost = scsi_host_get(shost);
+        if (!data->shost)
+                goto err;
+        init_completion(&data->prev_finished);
+
+        spin_lock(&async_scan_lock);
+        shost->async_scan = 1;
+        if (list_empty(&scanning_hosts))
+                complete(&data->prev_finished);
+        list_add_tail(&data->list, &scanning_hosts);
+        spin_unlock(&async_scan_lock);
+
+        return data;
+
+ err:
+        kfree(data);
+        return NULL;
+}
+
+/**
+ * scsi_finish_async_scan - asynchronous scan has finished
+ * @data: cookie returned from earlier call to scsi_prep_async_scan()
+ *
+ * All the devices currently attached to this host have been found.
+ * This function announces all the devices it has found to the rest
+ * of the system.
+ */
+void scsi_finish_async_scan(struct async_scan_data *data)
+{
+        struct Scsi_Host *shost;
+
+        if (!data)
+                return;
+
+        shost = data->shost;
+        if (!shost->async_scan) {
+                printk("%s called twice for host %d", __FUNCTION__,
+                                shost->host_no);
+                dump_stack();
+                return;
+        }
+
+        wait_for_completion(&data->prev_finished);
+
+        scsi_sysfs_add_devices(shost);
+
+        spin_lock(&async_scan_lock);
+        shost->async_scan = 0;
+        list_del(&data->list);
+        if (!list_empty(&scanning_hosts)) {
+                struct async_scan_data *next = list_entry(scanning_hosts.next,
+                                struct async_scan_data, list);
+                complete(&next->prev_finished);
+        }
+        spin_unlock(&async_scan_lock);
+
+        scsi_host_put(shost);
+        kfree(data);
+}
+
+static int do_scan_async(void *_data)
+{
+        struct async_scan_data *data = _data;
+        scsi_scan_host_selected(data->shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
+                                SCAN_WILD_CARD, 0);
+
+        scsi_finish_async_scan(data);
+        return 0;
+}
+
 /**
  * scsi_scan_host - scan the given adapter
  * @shost:      adapter to scan
  **/
 void scsi_scan_host(struct Scsi_Host *shost)
 {
-        scsi_scan_host_selected(shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
-                                SCAN_WILD_CARD, 0);
+        struct async_scan_data *data;
+
+        if (strncmp(scsi_scan_type, "none", 4) == 0)
+                return;
+
+        data = scsi_prep_async_scan(shost);
+        if (!data) {
+                scsi_scan_host_selected(shost, SCAN_WILD_CARD, SCAN_WILD_CARD,
+                                        SCAN_WILD_CARD, 0);
+                return;
+        }
+        kthread_run(do_scan_async, data, "scsi_scan_%d", shost->host_no);
 }
 EXPORT_SYMBOL(scsi_scan_host);