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Subject[PATCH 2/2] ubi: Expose the bitrot interface
Date
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>
---
drivers/mtd/ubi/cdev.c | 30 ++++++++
drivers/mtd/ubi/ubi.h | 1 +
drivers/mtd/ubi/wl.c | 144 ++++++++++++++++++++++++++++++++++++
include/uapi/mtd/ubi-user.h | 5 ++
4 files changed, 180 insertions(+)

diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 22547d7a84ea..947a8adbc799 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -974,6 +974,36 @@ static long ubi_cdev_ioctl(struct file *file, unsigned int cmd,
break;
}

+ /* Check a specific PEB for bitflips and scrub it if needed */
+ case UBI_IOCRPEB:
+ {
+ int pnum;
+
+ err = get_user(pnum, (__user int32_t *)argp);
+ if (err) {
+ err = -EFAULT;
+ break;
+ }
+
+ err = ubi_bitflip_check(ubi, pnum, 0);
+ break;
+ }
+
+ /* Force scrubbing for a specific PEB */
+ case UBI_IOCSPEB:
+ {
+ int pnum;
+
+ err = get_user(pnum, (__user int32_t *)argp);
+ if (err) {
+ err = -EFAULT;
+ break;
+ }
+
+ err = ubi_bitflip_check(ubi, pnum, 1);
+ break;
+ }
+
default:
err = -ENOTTY;
break;
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index d47b9e436e67..a1b9e764d489 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -929,6 +929,7 @@ int ubi_wl_put_fm_peb(struct ubi_device *ubi, struct ubi_wl_entry *used_e,
int ubi_is_erase_work(struct ubi_work *wrk);
void ubi_refill_pools(struct ubi_device *ubi);
int ubi_ensure_anchor_pebs(struct ubi_device *ubi);
+int ubi_bitflip_check(struct ubi_device *ubi, int pnum, int force_scrub);

/* io.c */
int ubi_io_read(const struct ubi_device *ubi, void *buf, int pnum, int offset,
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index ca1b31385eb5..5540599a60c6 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -1440,6 +1440,150 @@ int ubi_wl_flush(struct ubi_device *ubi, int vol_id, int lnum)
return err;
}

+static bool scrub_possible(struct ubi_device *ubi, struct ubi_wl_entry *e)
+{
+ if (in_wl_tree(e, &ubi->scrub))
+ return false;
+ else if (in_wl_tree(e, &ubi->erroneous))
+ return false;
+ else if (ubi->move_from == e)
+ return false;
+ else if (ubi->move_to == e)
+ return false;
+
+ return true;
+}
+
+/**
+ * ubi_bitflip_check - Check an eraseblock for bitflips and scrub it if needed.
+ * @ubi: UBI device description object
+ * @pnum: the physical eraseblock to schedule
+ * @force_scrub: force scrubbing if non-zero, schedule erase otherwise
+ *
+ * This function reads the given eraseblock and checks if bitflips occured.
+ * In case of bitflips, the eraseblock is scheduled for scrubbing.
+ * If scrubbing is forced with @force_scrub, the eraseblock is not read,
+ * but scheduled for scrubbing right away.
+ *
+ * Returns:
+ * %EINVAL, PEB is out of range
+ * %ENOENT, PEB is no longer used by UBI
+ * %EBUSY, PEB cannot be checked now or a check is currently running on it
+ * %EAGAIN, bit flips happened but scrubbing is currently not possible
+ * %EUCLEAN, bit flips happened and PEB is scheduled for scrubbing
+ * %0, no bit flips detected
+ */
+int ubi_bitflip_check(struct ubi_device *ubi, int pnum, int force_scrub)
+{
+ int err;
+ struct ubi_wl_entry *e;
+
+ if (pnum < 0 || pnum >= ubi->peb_count) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ /*
+ * Pause all parallel work, otherwise it can happen that the
+ * erase worker frees a wl entry under us.
+ */
+ down_write(&ubi->work_sem);
+
+ /*
+ * Make sure that the wl entry does not change state while
+ * inspecting it.
+ */
+ spin_lock(&ubi->wl_lock);
+ e = ubi->lookuptbl[pnum];
+ if (!e) {
+ spin_unlock(&ubi->wl_lock);
+ err = -ENOENT;
+ goto out_resume;
+ }
+
+ /*
+ * Does it make sense to check this PEB?
+ */
+ if (!scrub_possible(ubi, e)) {
+ spin_unlock(&ubi->wl_lock);
+ err = -EBUSY;
+ goto out_resume;
+ }
+ spin_unlock(&ubi->wl_lock);
+
+ if (!force_scrub) {
+ mutex_lock(&ubi->buf_mutex);
+ err = ubi_io_read(ubi, ubi->peb_buf, pnum, 0, ubi->peb_size);
+ mutex_unlock(&ubi->buf_mutex);
+ }
+
+ if (err == UBI_IO_BITFLIPS || force_scrub) {
+ /*
+ * Okay, bit flip happened, let's figure out what we can do.
+ */
+ spin_lock(&ubi->wl_lock);
+
+ /*
+ * Recheck. We released wl_lock, UBI might have killed the
+ * wl entry under us.
+ */
+ e = ubi->lookuptbl[pnum];
+ if (!e) {
+ spin_unlock(&ubi->wl_lock);
+ err = -ENOENT;
+ goto out_resume;
+ }
+
+ /*
+ * Need to re-check state
+ */
+ if (!scrub_possible(ubi, e)) {
+ spin_unlock(&ubi->wl_lock);
+ err = -EBUSY;
+ goto out_resume;
+ }
+
+ if (in_pq(ubi, e)) {
+ prot_queue_del(ubi, e->pnum);
+ wl_tree_add(e, &ubi->scrub);
+ spin_unlock(&ubi->wl_lock);
+
+ err = ensure_wear_leveling(ubi, 1);
+ } else if (in_wl_tree(e, &ubi->used)) {
+ rb_erase(&e->u.rb, &ubi->used);
+ wl_tree_add(e, &ubi->scrub);
+ spin_unlock(&ubi->wl_lock);
+
+ err = ensure_wear_leveling(ubi, 1);
+ } else if (in_wl_tree(e, &ubi->free)) {
+ rb_erase(&e->u.rb, &ubi->free);
+ ubi->free_count--;
+ spin_unlock(&ubi->wl_lock);
+
+ /*
+ * This PEB is empty we can schedule it for
+ * erasure right away. No wear leveling needed.
+ */
+ err = schedule_erase(ubi, e, UBI_UNKNOWN, UBI_UNKNOWN,
+ force_scrub ? 0 : 1, true);
+ } else {
+ spin_unlock(&ubi->wl_lock);
+ err = -EAGAIN;
+ }
+
+ if (!err && !force_scrub)
+ err = -EUCLEAN;
+ } else {
+ err = 0;
+ }
+
+out_resume:
+ up_write(&ubi->work_sem);
+out:
+
+ return err;
+}
+
/**
* tree_destroy - destroy an RB-tree.
* @ubi: UBI device description object
diff --git a/include/uapi/mtd/ubi-user.h b/include/uapi/mtd/ubi-user.h
index aad3b6201fc0..b69e9ba6742b 100644
--- a/include/uapi/mtd/ubi-user.h
+++ b/include/uapi/mtd/ubi-user.h
@@ -171,6 +171,11 @@
/* Re-name volumes */
#define UBI_IOCRNVOL _IOW(UBI_IOC_MAGIC, 3, struct ubi_rnvol_req)

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

#define UBI_CTRL_IOC_MAGIC 'o'
--
2.19.1
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