[SCSI] Add Kconfig option for asynchronous SCSI scanning

Without this patch, the user has to add a kernel command line parameter
to get asynchronous SCSI scanning.  Now they can select the default at
compile time and still override it at boot time if they need to.

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

2 files changed, 24 insertions, 1 deletions

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 5881464a938d..8442be1bb162 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -216,6 +216,23 @@ config SCSI_LOGGING
           there should be no noticeable performance impact as long as you have
           logging turned off.
 
+config SCSI_SCAN_ASYNC
+        bool "Asynchronous SCSI scanning"
+        depends on SCSI
+        help
+          The SCSI subsystem can probe for devices while the rest of the
+          system continues booting, and even probe devices on different
+          busses in parallel, leading to a significant speed-up.
+          If you have built SCSI as modules, enabling this option can
+          be a problem as the devices may not have been found by the
+          time your system expects them to have been.  You can load the
+          scsi_wait_scan module to ensure that all scans have completed.
+          If you build your SCSI drivers into the kernel, then everything
+          will work fine if you say Y here.
+
+          You can override this choice by specifying scsi_mod.scan="sync"
+          or "async" on the kernel's command line.
+
 menu "SCSI Transports"
         depends on SCSI
 
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index aa1b1e0e9d22..d91d268dd331 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -89,7 +89,13 @@ 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";
+#ifdef CONFIG_SCSI_SCAN_ASYNC
+#define SCSI_SCAN_TYPE_DEFAULT "async"
+#else
+#define SCSI_SCAN_TYPE_DEFAULT "sync"
+#endif
+
+static char scsi_scan_type[6] = SCSI_SCAN_TYPE_DEFAULT;
 
 module_param_string(scan, scsi_scan_type, sizeof(scsi_scan_type), S_IRUGO);
 MODULE_PARM_DESC(scan, "sync, async or none");