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>

3 files changed, 34 insertions, 6 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)
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index e9874e7fcdf9..ae7aec3cabee 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -525,7 +525,7 @@ struct unixware_disklabel {
 #define ADDPART_FLAG_RAID       1
 #define ADDPART_FLAG_WHOLEDISK  2
 
-extern dev_t blk_lookup_devt(const char *name);
+extern dev_t blk_lookup_devt(const char *name, int part);
 extern char *disk_name (struct gendisk *hd, int part, char *buf);
 
 extern int rescan_partitions(struct gendisk *disk, struct block_device *bdev);
@@ -553,7 +553,7 @@ static inline struct block_device *bdget_disk(struct gendisk *disk, int index)
 
 static inline void printk_all_partitions(void) { }
 
-static inline dev_t blk_lookup_devt(const char *name)
+static inline dev_t blk_lookup_devt(const char *name, int part)
 {
         dev_t devt = MKDEV(0, 0);
         return devt;
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3885e70e7759..660c1e50c91b 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -76,6 +76,7 @@ dev_t name_to_dev_t(char *name)
         char s[32];
         char *p;
         dev_t res = 0;
+        int part;
 
         if (strncmp(name, "/dev/", 5) != 0) {
                 unsigned maj, min;
@@ -106,7 +107,31 @@ dev_t name_to_dev_t(char *name)
         for (p = s; *p; p++)
                 if (*p == '/')
                         *p = '!';
-        res = blk_lookup_devt(s);
+        res = blk_lookup_devt(s, 0);
+        if (res)
+                goto done;
+
+        /*
+         * try non-existant, but valid partition, which may only exist
+         * after revalidating the disk, like partitioned md devices
+         */
+        while (p > s && isdigit(p[-1]))
+                p--;
+        if (p == s || !*p || *p == '0')
+                goto fail;
+
+        /* try disk name without <part number> */
+        part = simple_strtoul(p, NULL, 10);
+        *p = '\0';
+        res = blk_lookup_devt(s, part);
+        if (res)
+                goto done;
+
+        /* try disk name without p<part number> */
+        if (p < s + 2 || !isdigit(p[-2]) || p[-1] != 'p')
+                goto fail;
+        p[-1] = '\0';
+        res = blk_lookup_devt(s, part);
         if (res)
                 goto done;