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richardweinbergerrichardweinberger
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ubi: Expose the bitrot interface
Using UBI_IOCRPEB and UBI_IOCSPEB userspace can force reading and scrubbing of PEBs. In case of bitflips UBI will automatically take action and move data to a different PEB. This interface allows a daemon to foster your NAND. Signed-off-by: Richard Weinberger <richard@nod.at>
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‎drivers/mtd/ubi/cdev.c

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -974,6 +974,36 @@ static long ubi_cdev_ioctl(struct file *file, unsigned int cmd,
974974
break;
975975
}
976976

977+
/* Check a specific PEB for bitflips and scrub it if needed */
978+
case UBI_IOCRPEB:
979+
{
980+
int pnum;
981+
982+
err = get_user(pnum, (__user int32_t *)argp);
983+
if (err) {
984+
err = -EFAULT;
985+
break;
986+
}
987+
988+
err = ubi_bitflip_check(ubi, pnum, 0);
989+
break;
990+
}
991+
992+
/* Force scrubbing for a specific PEB */
993+
case UBI_IOCSPEB:
994+
{
995+
int pnum;
996+
997+
err = get_user(pnum, (__user int32_t *)argp);
998+
if (err) {
999+
err = -EFAULT;
1000+
break;
1001+
}
1002+
1003+
err = ubi_bitflip_check(ubi, pnum, 1);
1004+
break;
1005+
}
1006+
9771007
default:
9781008
err = -ENOTTY;
9791009
break;

‎drivers/mtd/ubi/ubi.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -929,6 +929,7 @@ int ubi_wl_put_fm_peb(struct ubi_device *ubi, struct ubi_wl_entry *used_e,
929929
int ubi_is_erase_work(struct ubi_work *wrk);
930930
void ubi_refill_pools(struct ubi_device *ubi);
931931
int ubi_ensure_anchor_pebs(struct ubi_device *ubi);
932+
int ubi_bitflip_check(struct ubi_device *ubi, int pnum, int force_scrub);
932933

933934
/* io.c */
934935
int ubi_io_read(const struct ubi_device *ubi, void *buf, int pnum, int offset,

‎drivers/mtd/ubi/wl.c

Lines changed: 144 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1440,6 +1440,150 @@ int ubi_wl_flush(struct ubi_device *ubi, int vol_id, int lnum)
14401440
return err;
14411441
}
14421442

1443+
static bool scrub_possible(struct ubi_device *ubi, struct ubi_wl_entry *e)
1444+
{
1445+
if (in_wl_tree(e, &ubi->scrub))
1446+
return false;
1447+
else if (in_wl_tree(e, &ubi->erroneous))
1448+
return false;
1449+
else if (ubi->move_from == e)
1450+
return false;
1451+
else if (ubi->move_to == e)
1452+
return false;
1453+
1454+
return true;
1455+
}
1456+
1457+
/**
1458+
* ubi_bitflip_check - Check an eraseblock for bitflips and scrub it if needed.
1459+
* @ubi: UBI device description object
1460+
* @pnum: the physical eraseblock to schedule
1461+
* @force: dont't read the block, assume bitflips happened and take action.
1462+
*
1463+
* This function reads the given eraseblock and checks if bitflips occured.
1464+
* In case of bitflips, the eraseblock is scheduled for scrubbing.
1465+
* If scrubbing is forced with @force, the eraseblock is not read,
1466+
* but scheduled for scrubbing right away.
1467+
*
1468+
* Returns:
1469+
* %EINVAL, PEB is out of range
1470+
* %ENOENT, PEB is no longer used by UBI
1471+
* %EBUSY, PEB cannot be checked now or a check is currently running on it
1472+
* %EAGAIN, bit flips happened but scrubbing is currently not possible
1473+
* %EUCLEAN, bit flips happened and PEB is scheduled for scrubbing
1474+
* %0, no bit flips detected
1475+
*/
1476+
int ubi_bitflip_check(struct ubi_device *ubi, int pnum, int force)
1477+
{
1478+
int err;
1479+
struct ubi_wl_entry *e;
1480+
1481+
if (pnum < 0 || pnum >= ubi->peb_count) {
1482+
err = -EINVAL;
1483+
goto out;
1484+
}
1485+
1486+
/*
1487+
* Pause all parallel work, otherwise it can happen that the
1488+
* erase worker frees a wl entry under us.
1489+
*/
1490+
down_write(&ubi->work_sem);
1491+
1492+
/*
1493+
* Make sure that the wl entry does not change state while
1494+
* inspecting it.
1495+
*/
1496+
spin_lock(&ubi->wl_lock);
1497+
e = ubi->lookuptbl[pnum];
1498+
if (!e) {
1499+
spin_unlock(&ubi->wl_lock);
1500+
err = -ENOENT;
1501+
goto out_resume;
1502+
}
1503+
1504+
/*
1505+
* Does it make sense to check this PEB?
1506+
*/
1507+
if (!scrub_possible(ubi, e)) {
1508+
spin_unlock(&ubi->wl_lock);
1509+
err = -EBUSY;
1510+
goto out_resume;
1511+
}
1512+
spin_unlock(&ubi->wl_lock);
1513+
1514+
if (!force) {
1515+
mutex_lock(&ubi->buf_mutex);
1516+
err = ubi_io_read(ubi, ubi->peb_buf, pnum, 0, ubi->peb_size);
1517+
mutex_unlock(&ubi->buf_mutex);
1518+
}
1519+
1520+
if (err == UBI_IO_BITFLIPS || force) {
1521+
/*
1522+
* Okay, bit flip happened, let's figure out what we can do.
1523+
*/
1524+
spin_lock(&ubi->wl_lock);
1525+
1526+
/*
1527+
* Recheck. We released wl_lock, UBI might have killed the
1528+
* wl entry under us.
1529+
*/
1530+
e = ubi->lookuptbl[pnum];
1531+
if (!e) {
1532+
spin_unlock(&ubi->wl_lock);
1533+
err = -ENOENT;
1534+
goto out_resume;
1535+
}
1536+
1537+
/*
1538+
* Need to re-check state
1539+
*/
1540+
if (!scrub_possible(ubi, e)) {
1541+
spin_unlock(&ubi->wl_lock);
1542+
err = -EBUSY;
1543+
goto out_resume;
1544+
}
1545+
1546+
if (in_pq(ubi, e)) {
1547+
prot_queue_del(ubi, e->pnum);
1548+
wl_tree_add(e, &ubi->scrub);
1549+
spin_unlock(&ubi->wl_lock);
1550+
1551+
err = ensure_wear_leveling(ubi, 1);
1552+
} else if (in_wl_tree(e, &ubi->used)) {
1553+
rb_erase(&e->u.rb, &ubi->used);
1554+
wl_tree_add(e, &ubi->scrub);
1555+
spin_unlock(&ubi->wl_lock);
1556+
1557+
err = ensure_wear_leveling(ubi, 1);
1558+
} else if (in_wl_tree(e, &ubi->free)) {
1559+
rb_erase(&e->u.rb, &ubi->free);
1560+
ubi->free_count--;
1561+
spin_unlock(&ubi->wl_lock);
1562+
1563+
/*
1564+
* This PEB is empty we can schedule it for
1565+
* erasure right away. No wear leveling needed.
1566+
*/
1567+
err = schedule_erase(ubi, e, UBI_UNKNOWN, UBI_UNKNOWN,
1568+
force ? 0 : 1, true);
1569+
} else {
1570+
spin_unlock(&ubi->wl_lock);
1571+
err = -EAGAIN;
1572+
}
1573+
1574+
if (!err && !force)
1575+
err = -EUCLEAN;
1576+
} else {
1577+
err = 0;
1578+
}
1579+
1580+
out_resume:
1581+
up_write(&ubi->work_sem);
1582+
out:
1583+
1584+
return err;
1585+
}
1586+
14431587
/**
14441588
* tree_destroy - destroy an RB-tree.
14451589
* @ubi: UBI device description object

‎include/uapi/mtd/ubi-user.h

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -171,6 +171,11 @@
171171
/* Re-name volumes */
172172
#define UBI_IOCRNVOL _IOW(UBI_IOC_MAGIC, 3, struct ubi_rnvol_req)
173173

174+
/* Read the specified PEB and scrub it if there are bitflips */
175+
#define UBI_IOCRPEB _IOW(UBI_IOC_MAGIC, 4, __s32)
176+
/* Force scrubbing on the specified PEB */
177+
#define UBI_IOCSPEB _IOW(UBI_IOC_MAGIC, 5, __s32)
178+
174179
/* ioctl commands of the UBI control character device */
175180

176181
#define UBI_CTRL_IOC_MAGIC 'o'

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