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Subject[PATCH] async scsi scanning, version 13
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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