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-rw-r--r--block/genhd.c38
1 files changed, 35 insertions, 3 deletions
diff --git a/block/genhd.c b/block/genhd.c
index ee4b13520e5..67e5a59ced2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -299,6 +299,38 @@ EXPORT_SYMBOL(unregister_blkdev);
static struct kobj_map *bdev_map;
/**
+ * blk_mangle_minor - scatter minor numbers apart
+ * @minor: minor number to mangle
+ *
+ * Scatter consecutively allocated @minor number apart if MANGLE_DEVT
+ * is enabled. Mangling twice gives the original value.
+ *
+ * RETURNS:
+ * Mangled value.
+ *
+ * CONTEXT:
+ * Don't care.
+ */
+static int blk_mangle_minor(int minor)
+{
+#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
+ int i;
+
+ for (i = 0; i < MINORBITS / 2; i++) {
+ int low = minor & (1 << i);
+ int high = minor & (1 << (MINORBITS - 1 - i));
+ int distance = MINORBITS - 1 - 2 * i;
+
+ minor ^= low | high; /* clear both bits */
+ low <<= distance; /* swap the positions */
+ high >>= distance;
+ minor |= low | high; /* and set */
+ }
+#endif
+ return minor;
+}
+
+/**
* blk_alloc_devt - allocate a dev_t for a partition
* @part: partition to allocate dev_t for
* @gfp_mask: memory allocation flag
@@ -339,7 +371,7 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
return -EBUSY;
}
- *devt = MKDEV(BLOCK_EXT_MAJOR, idx);
+ *devt = MKDEV(BLOCK_EXT_MAJOR, blk_mangle_minor(idx));
return 0;
}
@@ -361,7 +393,7 @@ void blk_free_devt(dev_t devt)
if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
mutex_lock(&ext_devt_mutex);
- idr_remove(&ext_devt_idr, MINOR(devt));
+ idr_remove(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
mutex_unlock(&ext_devt_mutex);
}
}
@@ -473,7 +505,7 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
struct hd_struct *part;
mutex_lock(&ext_devt_mutex);
- part = idr_find(&ext_devt_idr, MINOR(devt));
+ part = idr_find(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
if (part && get_disk(part_to_disk(part))) {
*partno = part->partno;
disk = part_to_disk(part);