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xfs: add helpers to collect and sift btree block pointers during repair

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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@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
This commit is contained in:
Darrick J. Wong 2018-05-29 22:18:09 -07:00
parent 73d6b42aa4
commit 64a39d876e
2 changed files with 245 additions and 0 deletions
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217
fs/xfs/scrub/repair.c
View file

@ -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

28
fs/xfs/scrub/repair.h
View file

@ -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);