From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Add some helpers to assemble a list of fs block extents. Generally,
repair functions will iterate the rmapbt to make a list (1) of all
extents owned by the nominal owner of the metadata structure; then they
will iterate all other structures with the same rmap owner to make a
list (2) of active blocks; and finally we have a subtraction function to
subtract all the blocks in (2) from (1), with the result that (1) is now
a list of blocks that were owned by the old btree and must be disposed.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
v2: document the design of how repair functions are supposed to work,
implement review comments
---
fs/xfs/scrub/repair.c | 217 +++++++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/scrub/repair.h | 28 ++++++
2 files changed, 245 insertions(+)
diff --git a/fs/xfs/scrub/repair.c b/fs/xfs/scrub/repair.c
index be21a2984001..fca8e3c7887d 100644
--- a/fs/xfs/scrub/repair.c
+++ b/fs/xfs/scrub/repair.c
@@ -368,3 +368,220 @@ xfs_repair_init_btblock(
return 0;
}
+
+/*
+ * Reconstructing per-AG Btrees
+ *
+ * When a space btree is corrupt, we don't bother trying to fix it. Instead,
+ * we scan secondary space metadata to derive the records that should be in
+ * the damaged btree, initialize a fresh btree root, and insert the records.
+ * Note that for rebuilding the rmapbt we scan all the primary data to
+ * generate the new records.
+ *
+ * However, that leaves the matter of removing all the metadata describing the
+ * old broken structure. For primary metadata we use the rmap data to collect
+ * every extent with a matching rmap owner (exlist); we then iterate all other
+ * metadata structures with the same rmap owner to collect the extents that
+ * cannot be removed (sublist). We then subtract sublist from exlist to
+ * derive the blocks that were used by the old btree. These blocks can be
+ * reaped.
+ *
+ * For rmapbt reconstructions we must use different tactics for extent
+ * collection. First we iterate all primary metadata (this excludes the old
+ * rmapbt, obviously) to generate new rmap records. The gaps in the rmap
+ * records are collected as exlist. The bnobt records are collected as
+ * sublist. As with the other btrees we subtract sublist from exlist, and the
+ * result (since the rmapbt lives in the free space) are the blocks from the
+ * old rmapbt.
+ */
+
+/* Collect a dead btree extent for later disposal. */
+int
+xfs_repair_collect_btree_extent(
+ struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *exlist,
+ xfs_fsblock_t fsbno,
+ xfs_extlen_t len)
+{
+ struct xfs_repair_extent *rex;
+
+ trace_xfs_repair_collect_btree_extent(sc->mp,
+ XFS_FSB_TO_AGNO(sc->mp, fsbno),
+ XFS_FSB_TO_AGBNO(sc->mp, fsbno), len);
+
+ rex = kmem_alloc(sizeof(struct xfs_repair_extent), KM_MAYFAIL);
+ if (!rex)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&rex->list);
+ rex->fsbno = fsbno;
+ rex->len = len;
+ list_add_tail(&rex->list, &exlist->list);
+
+ return 0;
+}
+
+/*
+ * An error happened during the rebuild so the transaction will be cancelled.
+ * The fs will shut down, and the administrator has to unmount and run repair.
+ * Therefore, free all the memory associated with the list so we can die.
+ */
+void
+xfs_repair_cancel_btree_extents(
+ struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *exlist)
+{
+ struct xfs_repair_extent *rex;
+ struct xfs_repair_extent *n;
+
+ for_each_xfs_repair_extent_safe(rex, n, exlist) {
+ list_del(&rex->list);
+ kmem_free(rex);
+ }
+}
+
+/* Compare two btree extents. */
+static int
+xfs_repair_btree_extent_cmp(
+ void *priv,
+ struct list_head *a,
+ struct list_head *b)
+{
+ struct xfs_repair_extent *ap;
+ struct xfs_repair_extent *bp;
+
+ ap = container_of(a, struct xfs_repair_extent, list);
+ bp = container_of(b, struct xfs_repair_extent, list);
+
+ if (ap->fsbno > bp->fsbno)
+ return 1;
+ if (ap->fsbno < bp->fsbno)
+ return -1;
+ return 0;
+}
+
+/*
+ * Remove all the blocks mentioned in @sublist from the extents in @exlist.
+ *
+ * The intent is that callers will iterate the rmapbt for all of its records
+ * for a given owner to generate @exlist; and iterate all the blocks of the
+ * metadata structures that are not being rebuilt and have the same rmapbt
+ * owner to generate @sublist. This routine subtracts all the extents
+ * mentioned in sublist from all the extents linked in @exlist, which leaves
+ * @exlist as the list of blocks that are not accounted for, which we assume
+ * are the dead blocks of the old metadata structure. The blocks mentioned in
+ * @exlist can be reaped.
+ */
+#define LEFT_ALIGNED (1 << 0)
+#define RIGHT_ALIGNED (1 << 1)
+int
+xfs_repair_subtract_extents(
+ struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *exlist,
+ struct xfs_repair_extent_list *sublist)
+{
+ struct list_head *lp;
+ struct xfs_repair_extent *ex;
+ struct xfs_repair_extent *newex;
+ struct xfs_repair_extent *subex;
+ xfs_fsblock_t sub_fsb;
+ xfs_extlen_t sub_len;
+ int state;
+ int error = 0;
+
+ if (list_empty(&exlist->list) || list_empty(&sublist->list))
+ return 0;
+ ASSERT(!list_empty(&sublist->list));
+
+ list_sort(NULL, &exlist->list, xfs_repair_btree_extent_cmp);
+ list_sort(NULL, &sublist->list, xfs_repair_btree_extent_cmp);
+
+ /*
+ * Now that we've sorted both lists, we iterate exlist once, rolling
+ * forward through sublist and/or exlist as necessary until we find an
+ * overlap or reach the end of either list. We do not reset lp to the
+ * head of exlist nor do we reset subex to the head of sublist. The
+ * list traversal is similar to merge sort, but we're deleting
+ * instead. In this manner we avoid O(n^2) operations.
+ */
+ subex = list_first_entry(&sublist->list, struct xfs_repair_extent,
+ list);
+ lp = exlist->list.next;
+ while (lp != &exlist->list) {
+ ex = list_entry(lp, struct xfs_repair_extent, list);
+
+ /*
+ * Advance subex and/or ex until we find a pair that
+ * intersect or we run out of extents.
+ */
+ while (subex->fsbno + subex->len <= ex->fsbno) {
+ if (list_is_last(&subex->list, &sublist->list))
+ goto out;
+ subex = list_next_entry(subex, list);
+ }
+ if (subex->fsbno >= ex->fsbno + ex->len) {
+ lp = lp->next;
+ continue;
+ }
+
+ /* trim subex to fit the extent we have */
+ sub_fsb = subex->fsbno;
+ sub_len = subex->len;
+ if (subex->fsbno < ex->fsbno) {
+ sub_len -= ex->fsbno - subex->fsbno;
+ sub_fsb = ex->fsbno;
+ }
+ if (sub_len > ex->len)
+ sub_len = ex->len;
+
+ state = 0;
+ if (sub_fsb == ex->fsbno)
+ state |= LEFT_ALIGNED;
+ if (sub_fsb + sub_len == ex->fsbno + ex->len)
+ state |= RIGHT_ALIGNED;
+ switch (state) {
+ case LEFT_ALIGNED:
+ /* Coincides with only the left. */
+ ex->fsbno += sub_len;
+ ex->len -= sub_len;
+ break;
+ case RIGHT_ALIGNED:
+ /* Coincides with only the right. */
+ ex->len -= sub_len;
+ lp = lp->next;
+ break;
+ case LEFT_ALIGNED | RIGHT_ALIGNED:
+ /* Total overlap, just delete ex. */
+ lp = lp->next;
+ list_del(&ex->list);
+ kmem_free(ex);
+ break;
+ case 0:
+ /*
+ * Deleting from the middle: add the new right extent
+ * and then shrink the left extent.
+ */
+ newex = kmem_alloc(sizeof(struct xfs_repair_extent),
+ KM_MAYFAIL);
+ if (!newex) {
+ error = -ENOMEM;
+ goto out;
+ }
+ INIT_LIST_HEAD(&newex->list);
+ newex->fsbno = sub_fsb + sub_len;
+ newex->len = ex->fsbno + ex->len - newex->fsbno;
+ list_add(&newex->list, &ex->list);
+ ex->len = sub_fsb - ex->fsbno;
+ lp = lp->next;
+ break;
+ default:
+ ASSERT(0);
+ break;
+ }
+ }
+
+out:
+ return error;
+}
+#undef LEFT_ALIGNED
+#undef RIGHT_ALIGNED
diff --git a/fs/xfs/scrub/repair.h b/fs/xfs/scrub/repair.h
index 40990fa5f381..ba1fdd7b9a79 100644
--- a/fs/xfs/scrub/repair.h
+++ b/fs/xfs/scrub/repair.h
@@ -43,6 +43,34 @@ int xfs_repair_init_btblock(struct xfs_scrub_context *sc, xfs_fsblock_t fsb,
struct xfs_buf **bpp, xfs_btnum_t btnum,
const struct xfs_buf_ops *ops);
+struct xfs_repair_extent {
+ struct list_head list;
+ xfs_fsblock_t fsbno;
+ xfs_extlen_t len;
+};
+
+struct xfs_repair_extent_list {
+ struct list_head list;
+};
+
+static inline void
+xfs_repair_init_extent_list(
+ struct xfs_repair_extent_list *exlist)
+{
+ INIT_LIST_HEAD(&exlist->list);
+}
+
+#define for_each_xfs_repair_extent_safe(rbe, n, exlist) \
+ list_for_each_entry_safe((rbe), (n), &(exlist)->list, list)
+int xfs_repair_collect_btree_extent(struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *btlist, xfs_fsblock_t fsbno,
+ xfs_extlen_t len);
+void xfs_repair_cancel_btree_extents(struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *btlist);
+int xfs_repair_subtract_extents(struct xfs_scrub_context *sc,
+ struct xfs_repair_extent_list *exlist,
+ struct xfs_repair_extent_list *sublist);
+
/* Metadata repairers */
int xfs_repair_probe(struct xfs_scrub_context *sc);
--
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