diff options
Diffstat (limited to 'block/genhd.c')
| -rw-r--r-- | block/genhd.c | 38 |
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); |