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".

[bunk@stusta.de: root_wait can become static]
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a0362d5a911eadb08246376519d57bf54c5aabf2..a571495a9ac6c3bce9b3fe4ee75b908af1a90b9d 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1504,6 +1504,10 @@ and is between 256 and 4096 characters. It is defined in the file
 
        rootfstype=     [KNL] Set root filesystem type
 
+       rootwait        [KNL] Wait (indefinitely) for root device to show up.
+                       Useful for devices that are detected asynchronously
+                       (e.g. USB and MMC devices).
+
        rw              [KNL] Mount root device read-write on boot
 
        S               [KNL] Run init in single mode

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 46fe407fb03eb6be6236378be2daa79a61cd5aa1..4efa1e5385e3a1b110b29b46ceccedf36a8c4138 100644 (file)
--- 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];
+static int __initdata root_wait;
 
 dev_t ROOT_DEV;
 
@@ -216,6 +217,16 @@ static int __init root_dev_setup(char *line)
 
 __setup("root=", root_dev_setup);
 
+static int __init rootwait_setup(char *str)
+{
+       if (*str)
+               return 0;
+       root_wait = 1;
+       return 1;
+}
+
+__setup("rootwait", rootwait_setup);
+
 static char * __initdata root_mount_data;
 static int __init root_data_setup(char *str)
 {
@@ -438,11 +449,20 @@ 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);
+               while (driver_probe_done() != 0 ||
+                       (ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
+                       msleep(100);
+       }
+
+       is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
+
        if (is_floppy && rd_doload && rd_load_disk(0))
                ROOT_DEV = Root_RAM0;