[PATCH] Make prepare_namespace() wait for devices

[Pierre Ossman <drzeus-list@drzeus.cx>]

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init: wait for asynchronously scanned block devices

Some buses (e.g. USB and MMC) do their scanning of devices in the
background, causing a race between them and prepare_namespace().
In order to be able to use these buses without an initrd, we now
wait for the device specified in root= to actually show up.

If the device never shows up than we will hang in an infinite loop.
In order to not mess with setups that reboot on panic, the feature
must be turned on via the command line option "rootwait".

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org

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commit bb8c44ee8b4d584295add58a4ea2f03b9938fc3c
Author: Pierre Ossman <drzeus@drzeus.cx>
Date:   Mon May 14 14:15:46 2007 +0200

    init: wait for asynchronously scanned block devices
    
    Some buses (e.g. USB and MMC) do their scanning of devices in the
    background, causing a race between them and prepare_namespace().
    In order to be able to use these buses without an initrd, we now
    wait for the device specified in root= to actually show up.
    
    If the device never shows up than we will hang in an infinite loop.
    In order to not mess with setups that reboot on panic, the feature
    must be turned on via the command line option "rootwait".
    
    Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 46fe407..efc134c 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -25,6 +25,7 @@ int __initdata rd_doload;	/* 1 = load RAM disk, 0 = don't load */
 int root_mountflags = MS_RDONLY | MS_SILENT;
 char * __initdata root_device_name;
 static char __initdata saved_root_name[64];
+int __initdata root_wait;
 
 dev_t ROOT_DEV;
 
@@ -216,6 +217,14 @@ static int __init root_dev_setup(char *line)
 
 __setup("root=", root_dev_setup);
 
+static int __init rootwait_setup(char *line)
+{
+	root_wait = simple_strtol(line,NULL,0);
+	return 1;
+}
+
+__setup("rootwait=", rootwait_setup);
+
 static char * __initdata root_mount_data;
 static int __init root_data_setup(char *str)
 {
@@ -438,11 +447,24 @@ void __init prepare_namespace(void)
 			root_device_name += 5;
 	}
 
-	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
-
 	if (initrd_load())
 		goto out;
 
+	/* wait for any asynchronous scanning to complete */
+	if ((ROOT_DEV == 0) && root_wait) {
+		printk(KERN_INFO "Waiting for root device %s...\n",
+			saved_root_name);
+		do {
+			while (driver_probe_done() != 0)
+				msleep(100);
+			ROOT_DEV = name_to_dev_t(saved_root_name);
+			if (ROOT_DEV == 0)
+				msleep(100);
+		} while (ROOT_DEV == 0);
+	}
+
+	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
+
 	if (is_floppy && rd_doload && rd_load_disk(0))
 		ROOT_DEV = Root_RAM0;