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block: implement CONFIG_DEBUG_BLOCK_EXT_DEVT

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Extended devt introduces non-contiguos device numbers.  This patch
implements a debug option which forces most devt allocations to be
from the extended area and spreads them out.  This is enabled by
default if DEBUG_KERNEL is set and achieves...

1. Detects code paths in kernel or userland which expect predetermined
   consecutive device numbers.

2. When something goes wrong, avoid corruption as adding to the minor
   of earlier partition won't lead to the wrong but valid device.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Tejun Heo 2008-08-25 19:47:25 +09:00 committed by Jens Axboe
parent f615b48cc7
commit 870d665612
4 changed files with 63 additions and 3 deletions
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38
block/genhd.c
View file

@ -298,6 +298,38 @@ 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
@ -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);

6
drivers/ide/ide-disk.c
View file

@ -42,7 +42,13 @@
#include <asm/div64.h>
#define IDE_DISK_PARTS (1 << PARTN_BITS)
#if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
#define IDE_DISK_MINORS IDE_DISK_PARTS
#else
#define IDE_DISK_MINORS 1
#endif
#define IDE_DISK_EXT_MINORS (IDE_DISK_PARTS - IDE_DISK_MINORS)
struct ide_disk_obj {

6
drivers/scsi/sd.c
View file

@ -87,7 +87,13 @@ MODULE_ALIAS_SCSI_DEVICE(TYPE_MOD);
MODULE_ALIAS_SCSI_DEVICE(TYPE_RBC);
#define SD_PARTS 64
#if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
#define SD_MINORS 16
#else
#define SD_MINORS 1
#endif
#define SD_EXT_MINORS (SD_PARTS - SD_MINORS)
static int sd_revalidate_disk(struct gendisk *);

16
lib/Kconfig.debug
View file

@ -624,6 +624,22 @@ config BACKTRACE_SELF_TEST
Say N if you are unsure.
config DEBUG_BLOCK_EXT_DEVT
bool "Force extended block device numbers and spread them"
depends on DEBUG_KERNEL
depends on BLOCK
default y
help
Conventionally, block device numbers are allocated from
predetermined contiguous area. However, extended block area
may introduce non-contiguous block device numbers. This
option forces most block device numbers to be allocated from
the extended space and spreads them to discover kernel or
userland code paths which assume predetermined contiguous
device number allocation.
Say N if you are unsure.
config LKDTM
tristate "Linux Kernel Dump Test Tool Module"
depends on DEBUG_KERNEL