+/*
+ * Adjust a set of pages, each page containing an array of lu_dirpages,
+ * so that each page can be used as a single logical lu_dirpage.
+ *
+ * A lu_dirpage is laid out as follows, where s = ldp_hash_start,
+ * e = ldp_hash_end, f = ldp_flags, p = padding, and each "ent" is a
+ * struct lu_dirent. It has size up to LU_PAGE_SIZE. The ldp_hash_end
+ * value is used as a cookie to request the next lu_dirpage in a
+ * directory listing that spans multiple pages (two in this example):
+ * ________
+ * | |
+ * .|--------v------- -----.
+ * |s|e|f|p|ent|ent| ... |ent|
+ * '--|-------------- -----' Each CFS_PAGE contains a single
+ * '------. lu_dirpage.
+ * .---------v------- -----.
+ * |s|e|f|p|ent| 0 | ... | 0 |
+ * '----------------- -----'
+ *
+ * However, on hosts where the native VM page size (CFS_PAGE_SIZE) is
+ * larger than LU_PAGE_SIZE, a single host page may contain multiple
+ * lu_dirpages. After reading the lu_dirpages from the MDS, the
+ * ldp_hash_end of the first lu_dirpage refers to the one immediately
+ * after it in the same CFS_PAGE (arrows simplified for brevity, but
+ * in general e0==s1, e1==s2, etc.):
+ *
+ * .-------------------- -----.
+ * |s0|e0|f0|p|ent|ent| ... |ent|
+ * |---v---------------- -----|
+ * |s1|e1|f1|p|ent|ent| ... |ent|
+ * |---v---------------- -----| Here, each CFS_PAGE contains
+ * ... multiple lu_dirpages.
+ * |---v---------------- -----|
+ * |s'|e'|f'|p|ent|ent| ... |ent|
+ * '---|---------------- -----'
+ * v
+ * .----------------------------.
+ * | next CFS_PAGE |
+ *
+ * This structure is transformed into a single logical lu_dirpage as follows:
+ *
+ * - Replace e0 with e' so the request for the next lu_dirpage gets the page
+ * labeled 'next CFS_PAGE'.
+ *
+ * - Copy the LDF_COLLIDE flag from f' to f0 to correctly reflect whether
+ * a hash collision with the next page exists.
+ *
+ * - Adjust the lde_reclen of the ending entry of each lu_dirpage to span
+ * to the first entry of the next lu_dirpage.
+ */
+#if CFS_PAGE_SIZE > LU_PAGE_SIZE
+static void lmv_adjust_dirpages(struct page **pages, int ncfspgs, int nlupgs)
+{
+ int i;
+
+ for (i = 0; i < ncfspgs; i++) {
+ struct lu_dirpage *dp = cfs_kmap(pages[i]);
+ struct lu_dirpage *first = dp;
+ struct lu_dirent *end_dirent = NULL;
+ struct lu_dirent *ent;
+ __u64 hash_end = dp->ldp_hash_end;
+ __u32 flags = dp->ldp_flags;
+
+ for (; nlupgs > 1; nlupgs--) {
+ ent = lu_dirent_start(dp);
+ for (end_dirent = ent; ent != NULL;
+ end_dirent = ent, ent = lu_dirent_next(ent));
+
+ /* Advance dp to next lu_dirpage. */
+ dp = (struct lu_dirpage *)((char *)dp + LU_PAGE_SIZE);
+
+ /* Check if we've reached the end of the CFS_PAGE. */
+ if (!((unsigned long)dp & ~CFS_PAGE_MASK))
+ break;
+
+ /* Save the hash and flags of this lu_dirpage. */
+ hash_end = dp->ldp_hash_end;
+ flags = dp->ldp_flags;
+
+ /* Check if lu_dirpage contains no entries. */
+ if (!end_dirent)
+ break;
+
+ /* Enlarge the end entry lde_reclen from 0 to
+ * first entry of next lu_dirpage. */
+ LASSERT(le16_to_cpu(end_dirent->lde_reclen) == 0);
+ end_dirent->lde_reclen =
+ cpu_to_le16((char *)(dp->ldp_entries) -
+ (char *)end_dirent);
+ }
+
+ first->ldp_hash_end = hash_end;
+ first->ldp_flags &= ~cpu_to_le32(LDF_COLLIDE);
+ first->ldp_flags |= flags & cpu_to_le32(LDF_COLLIDE);
+
+ cfs_kunmap(pages[i]);
+ }
+}
+#else
+#define lmv_adjust_dirpages(pages, ncfspgs, nlupgs) do {} while (0)
+#endif /* CFS_PAGE_SIZE > LU_PAGE_SIZE */
+