block: do_mounts - accept root=<non-existant partition>

Some devices, like md, may create partitions only at first access,
so allow root= to be set to a valid non-existant partition of an
existing disk. This applies only to non-initramfs root mounting.

This fixes a regression from 2.6.24 which did allow this to happen and
broke some users machines :(

Acked-by: Neil Brown <neilb@suse.de>
Tested-by: Joao Luis Meloni Assirati <assirati@nonada.if.usp.br>
Cc: stable <stable@kernel.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 3 deletions

diff --git a/block/genhd.c b/block/genhd.c
index fda9c7a63c29..129ad939f9dd 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -653,7 +653,7 @@ void genhd_media_change_notify(struct gendisk *disk)
 EXPORT_SYMBOL_GPL(genhd_media_change_notify);
 #endif  /*  0  */
 
-dev_t blk_lookup_devt(const char *name)
+dev_t blk_lookup_devt(const char *name, int part)
 {
         struct device *dev;
         dev_t devt = MKDEV(0, 0);
@@ -661,7 +661,11 @@ dev_t blk_lookup_devt(const char *name)
         mutex_lock(&block_class_lock);
         list_for_each_entry(dev, &block_class.devices, node) {
                 if (strcmp(dev->bus_id, name) == 0) {
-                        devt = dev->devt;
+                        struct gendisk *disk = dev_to_disk(dev);
+
+                        if (part < disk->minors)
+                                devt = MKDEV(MAJOR(dev->devt),
+                                             MINOR(dev->devt) + part);
                         break;
                 }
         }
@@ -669,7 +673,6 @@ dev_t blk_lookup_devt(const char *name)
 
         return devt;
 }
-
 EXPORT_SYMBOL(blk_lookup_devt);
 
 struct gendisk *alloc_disk(int minors)