[XFS] implement generic xfs_btree_decrement

From: Dave Chinner <dgc@sgi.com>

[hch: split out from bigger patch and minor adaptions]

SGI-PV: 985583

SGI-Modid: xfs-linux-melb:xfs-kern:32191a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Bill O'Donnell <billodo@sgi.com>
Signed-off-by: David Chinner <david@fromorbit.com>

1 files changed, 99 insertions, 0 deletions

diff --git a/fs/xfs/xfs_btree.c b/fs/xfs/xfs_btree.c
index e9ab86b7990e..3d561f8f78d0 100644
--- a/fs/xfs/xfs_btree.c
+++ b/fs/xfs/xfs_btree.c
@@ -1171,3 +1171,102 @@ error0:
         XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
         return error;
 }
+
+/*
+ * Decrement cursor by one record at the level.
+ * For nonzero levels the leaf-ward information is untouched.
+ */
+int                                             /* error */
+xfs_btree_decrement(
+        struct xfs_btree_cur    *cur,
+        int                     level,
+        int                     *stat)          /* success/failure */
+{
+        struct xfs_btree_block  *block;
+        xfs_buf_t               *bp;
+        int                     error;          /* error return value */
+        int                     lev;
+        union xfs_btree_ptr     ptr;
+
+        XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);
+        XFS_BTREE_TRACE_ARGI(cur, level);
+
+        ASSERT(level < cur->bc_nlevels);
+
+        /* Read-ahead to the left at this level. */
+        xfs_btree_readahead(cur, level, XFS_BTCUR_LEFTRA);
+
+        /* We're done if we remain in the block after the decrement. */
+        if (--cur->bc_ptrs[level] > 0)
+                goto out1;
+
+        /* Get a pointer to the btree block. */
+        block = xfs_btree_get_block(cur, level, &bp);
+
+#ifdef DEBUG
+        error = xfs_btree_check_block(cur, block, level, bp);
+        if (error)
+                goto error0;
+#endif
+
+        /* Fail if we just went off the left edge of the tree. */
+        xfs_btree_get_sibling(cur, block, &ptr, XFS_BB_LEFTSIB);
+        if (xfs_btree_ptr_is_null(cur, &ptr))
+                goto out0;
+
+        XFS_BTREE_STATS_INC(cur, decrement);
+
+        /*
+         * March up the tree decrementing pointers.
+         * Stop when we don't go off the left edge of a block.
+         */
+        for (lev = level + 1; lev < cur->bc_nlevels; lev++) {
+                if (--cur->bc_ptrs[lev] > 0)
+                        break;
+                /* Read-ahead the left block for the next loop. */
+                xfs_btree_readahead(cur, lev, XFS_BTCUR_LEFTRA);
+        }
+
+        /*
+         * If we went off the root then we are seriously confused.
+         * or the root of the tree is in an inode.
+         */
+        if (lev == cur->bc_nlevels) {
+                if (cur->bc_flags & XFS_BTREE_ROOT_IN_INODE)
+                        goto out0;
+                ASSERT(0);
+                error = EFSCORRUPTED;
+                goto error0;
+        }
+        ASSERT(lev < cur->bc_nlevels);
+
+        /*
+         * Now walk back down the tree, fixing up the cursor's buffer
+         * pointers and key numbers.
+         */
+        for (block = xfs_btree_get_block(cur, lev, &bp); lev > level; ) {
+                union xfs_btree_ptr     *ptrp;
+
+                ptrp = xfs_btree_ptr_addr(cur, cur->bc_ptrs[lev], block);
+                error = xfs_btree_read_buf_block(cur, ptrp, --lev,
+                                                        0, &block, &bp);
+                if (error)
+                        goto error0;
+                xfs_btree_setbuf(cur, lev, bp);
+                cur->bc_ptrs[lev] = xfs_btree_get_numrecs(block);
+        }
+out1:
+        XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
+        *stat = 1;
+        return 0;
+
+out0:
+        XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
+        *stat = 0;
+        return 0;
+
+error0:
+        XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
+        return error;
+}
+