[PATCH] async scsi scanning, version 13

[Matthew Wilcox <matthew@wil.cx>]

Version 13 ...

changes vs version 12:

Address akpm's comments:
 - use DEFINE_SPINLOCK
 - document how scsi_complete_async_scans works
 - document why the memory allocation loop in scsi_complete_async_scans
   will eventually terminate
 - document why we don't add ourselves to the list if it's already empty
    
shost_for_each_device is safe and shost_for_each_device_safe isn't.
Delete shost_for_each_device_safe, use shost_for_each_device and update
the docs for __shost_for_each_device and shost_for_each_device to be
more accurate.

changes vs version 11:

Fix whitespace pointed out by Randy Dunlap.

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5498324..4b687ef 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1426,6 +1426,11 @@ running once the system is up.
 
 	scsi_logging=	[SCSI]
 
+	scsi_mod.scan=	[SCSI] sync (default) scans SCSI busses as they are
+			discovered.  async scans them in kernel threads,
+			allowing boot to proceed.  none ignores them, expecting
+			user space to do the scan.
+
 	selinux		[SELINUX] Disable or enable SELinux at boot time.
 			Format: { "0" | "1" }
 			See security/selinux/Kconfig help text.
diff --git a/drivers/scsi/Makefile b/drivers/scsi/Makefile
index 1ef951b..38d0e25 100644
--- a/drivers/scsi/Makefile
+++ b/drivers/scsi/Makefile
@@ -140,6 +140,8 @@ obj-$(CONFIG_CHR_DEV_SCH)	+= ch.o
 # This goes last, so that "real" scsi devices probe earlier
 obj-$(CONFIG_SCSI_DEBUG)	+= scsi_debug.o
 
+obj-$(CONFIG_SCSI)		+= scsi_wait_scan.o
+
 scsi_mod-y			+= scsi.o hosts.o scsi_ioctl.o constants.o \
 				   scsicam.o scsi_error.o scsi_lib.o \
 				   scsi_scan.o scsi_sysfs.o \
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index 5d023d4..f458c2f 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -39,6 +39,9 @@ static inline void scsi_log_completion(s
 	{ };
 #endif
 
+/* scsi_scan.c */
+int scsi_complete_async_scans(void);
+
 /* scsi_devinfo.c */
 extern int scsi_get_device_flags(struct scsi_device *sdev,
 				 const unsigned char *vendor,
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index fd9e281..148e24c 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -29,7 +29,9 @@ #include <linux/module.h>
 #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_lu
 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_de
  *     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_devi
 	 * 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
 		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 *par
 {
 	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_
 		"%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_
 	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);
 
diff --git a/drivers/scsi/scsi_wait_scan.c b/drivers/scsi/scsi_wait_scan.c
new file mode 100644
index 0000000..f7aea46
--- /dev/null
+++ b/drivers/scsi/scsi_wait_scan.c
@@ -0,0 +1,31 @@
+/*
+ * scsi_wait_scan.c
+ *
+ * Copyright (C) 2006 James Bottomley <James.Bottomley@SteelEye.com>
+ *
+ * This is a simple module to wait until all the async scans are
+ * complete.  The idea is to use it in initrd/initramfs scripts.  You
+ * modprobe it after all the modprobes of the root SCSI drivers and it
+ * will wait until they have all finished scanning their busses before
+ * allowing the boot to proceed
+ */
+
+#include <linux/module.h>
+#include "scsi_priv.h"
+
+static int __init wait_scan_init(void)
+{
+	scsi_complete_async_scans();
+	return 0;
+}
+
+static void __exit wait_scan_exit(void)
+{
+}
+ 
+MODULE_DESCRIPTION("SCSI wait for scans");
+MODULE_AUTHOR("James Bottomley");
+MODULE_LICENSE("GPL");
+ 
+late_initcall(wait_scan_init);
+module_exit(wait_scan_exit);
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 895d212..0f75a48 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -223,13 +223,13 @@ extern struct scsi_device *__scsi_iterat
 						  struct scsi_device *);
 
 /**
- * shost_for_each_device  -  iterate over all devices of a host
- * @sdev:	iterator
- * @host:	host whiches devices we want to iterate over
+ * shost_for_each_device - iterate over all devices of a host
+ * @sdev: the &struct scsi_device to use as a cursor
+ * @shost: the &struct scsi_host to iterate over
  *
- * This traverses over each devices of @shost.  The devices have
- * a reference that must be released by scsi_host_put when breaking
- * out of the loop.
+ * Iterator that returns each device attached to @shost.  This loop
+ * takes a reference on each device and releases it at the end.  If
+ * you break out of the loop, you must call scsi_device_put(sdev).
  */
 #define shost_for_each_device(sdev, shost) \
 	for ((sdev) = __scsi_iterate_devices((shost), NULL); \
@@ -237,17 +237,17 @@ #define shost_for_each_device(sdev, shos
 	     (sdev) = __scsi_iterate_devices((shost), (sdev)))
 
 /**
- * __shost_for_each_device  -  iterate over all devices of a host (UNLOCKED)
- * @sdev:	iterator
- * @host:	host whiches devices we want to iterate over
+ * __shost_for_each_device - iterate over all devices of a host (UNLOCKED)
+ * @sdev: the &struct scsi_device to use as a cursor
+ * @shost: the &struct scsi_host to iterate over
  *
- * This traverses over each devices of @shost.  It does _not_ take a
- * reference on the scsi_device, thus it the whole loop must be protected
- * by shost->host_lock.
+ * Iterator that returns each device attached to @shost.  It does _not_
+ * take a reference on the scsi_device, so the whole loop must be
+ * protected by shost->host_lock.
  *
- * Note:  The only reason why drivers would want to use this is because
- * they're need to access the device list in irq context.  Otherwise you
- * really want to use shost_for_each_device instead.
+ * Note: The only reason to use this is because you need to access the
+ * device list in interrupt context.  Otherwise you really want to use
+ * shost_for_each_device instead.
  */
 #define __shost_for_each_device(sdev, shost) \
 	list_for_each_entry((sdev), &((shost)->__devices), siblings)
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 39c6f8c..ba5b3eb 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -552,6 +552,9 @@ struct Scsi_Host {
 	/* task mgmt function in progress */
 	unsigned tmf_in_progress:1;
 
+	/* Asynchronous scan in progress */
+	unsigned async_scan:1;
+
 	/*
 	 * Optional work queue to be utilized by the transport
 	 */
-
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