+ while (1) {
+ if (cur <= rsv->rsv_end)
+ cur = rsv->rsv_end + 1;
+
+ /* TODO?
+ * in the case we could not find a reservable space
+ * that is what is expected, during the re-search, we could
+ * remember what's the largest reservable space we could have
+ * and return that one.
+ *
+ * For now it will fail if we could not find the reservable
+ * space with expected-size (or more)...
+ */
+ if (cur > last_block)
+ return -1; /* fail */
+
+ prev = rsv;
+ next = rb_next(&rsv->rsv_node);
+ rsv = list_entry(next,struct ext3_reserve_window_node,rsv_node);
+
+ /*
+ * Reached the last reservation, we can just append to the
+ * previous one.
+ */
+ if (!next)
+ break;
+
+ if (cur + size <= rsv->rsv_start) {
+ /*
+ * Found a reserveable space big enough. We could
+ * have a reservation across the group boundary here
+ */
+ break;
+ }
+ }
+ /*
+ * we come here either :
+ * when we reach the end of the whole list,
+ * and there is empty reservable space after last entry in the list.
+ * append it to the end of the list.
+ *
+ * or we found one reservable space in the middle of the list,
+ * return the reservation window that we could append to.
+ * succeed.
+ */
+
+ if ((prev != my_rsv) && (!rsv_is_empty(&my_rsv->rsv_window)))
+ rsv_window_remove(sb, my_rsv);
+
+ /*
+ * Let's book the whole avaliable window for now. We will check the
+ * disk bitmap later and then, if there are free blocks then we adjust
+ * the window size if it's larger than requested.
+ * Otherwise, we will remove this node from the tree next time
+ * call find_next_reservable_window.
+ */
+ my_rsv->rsv_start = cur;
+ my_rsv->rsv_end = cur + size - 1;
+ my_rsv->rsv_alloc_hit = 0;
+
+ if (prev != my_rsv)
+ ext3_rsv_window_add(sb, my_rsv);
+
+ return 0;
+}
+
+/**
+ * alloc_new_reservation()--allocate a new reservation window
+ *
+ * To make a new reservation, we search part of the filesystem
+ * reservation list (the list that inside the group). We try to
+ * allocate a new reservation window near the allocation goal,
+ * or the beginning of the group, if there is no goal.
+ *
+ * We first find a reservable space after the goal, then from
+ * there, we check the bitmap for the first free block after
+ * it. If there is no free block until the end of group, then the
+ * whole group is full, we failed. Otherwise, check if the free
+ * block is inside the expected reservable space, if so, we
+ * succeed.
+ * If the first free block is outside the reservable space, then
+ * start from the first free block, we search for next available
+ * space, and go on.
+ *
+ * on succeed, a new reservation will be found and inserted into the list
+ * It contains at least one free block, and it does not overlap with other
+ * reservation windows.
+ *
+ * failed: we failed to find a reservation window in this group
+ *
+ * @rsv: the reservation
+ *
+ * @goal: The goal (group-relative). It is where the search for a
+ * free reservable space should start from.
+ * if we have a goal(goal >0 ), then start from there,
+ * no goal(goal = -1), we start from the first block
+ * of the group.
+ *
+ * @sb: the super block
+ * @group: the group we are trying to allocate in
+ * @bitmap_bh: the block group block bitmap
+ *
+ */
+static int alloc_new_reservation(struct ext3_reserve_window_node *my_rsv,
+ int goal, struct super_block *sb,
+ unsigned int group, struct buffer_head *bitmap_bh)
+{
+ struct ext3_reserve_window_node *search_head;
+ int group_first_block, group_end_block, start_block;
+ int first_free_block;
+ struct rb_root *fs_rsv_root = &EXT3_SB(sb)->s_rsv_window_root;
+ unsigned long size;
+ int ret;
+ spinlock_t *rsv_lock = &EXT3_SB(sb)->s_rsv_window_lock;
+
+ group_first_block = le32_to_cpu(EXT3_SB(sb)->s_es->s_first_data_block) +
+ group * EXT3_BLOCKS_PER_GROUP(sb);
+ group_end_block = group_first_block + EXT3_BLOCKS_PER_GROUP(sb) - 1;
+
+ if (goal < 0)
+ start_block = group_first_block;
+ else
+ start_block = goal + group_first_block;
+
+ size = my_rsv->rsv_goal_size;
+
+ if (!rsv_is_empty(&my_rsv->rsv_window)) {
+ /*
+ * if the old reservation is cross group boundary
+ * and if the goal is inside the old reservation window,
+ * we will come here when we just failed to allocate from
+ * the first part of the window. We still have another part
+ * that belongs to the next group. In this case, there is no
+ * point to discard our window and try to allocate a new one
+ * in this group(which will fail). we should
+ * keep the reservation window, just simply move on.
+ *
+ * Maybe we could shift the start block of the reservation
+ * window to the first block of next group.
+ */
+
+ if ((my_rsv->rsv_start <= group_end_block) &&
+ (my_rsv->rsv_end > group_end_block) &&
+ (start_block >= my_rsv->rsv_start))
+ return -1;
+
+ if ((my_rsv->rsv_alloc_hit >
+ (my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
+ /*
+ * if we previously allocation hit ration is greater than half
+ * we double the size of reservation window next time
+ * otherwise keep the same
+ */
+ size = size * 2;
+ if (size > EXT3_MAX_RESERVE_BLOCKS)
+ size = EXT3_MAX_RESERVE_BLOCKS;
+ my_rsv->rsv_goal_size= size;
+ }
+ }
+
+ spin_lock(rsv_lock);
+ /*
+ * shift the search start to the window near the goal block
+ */
+ search_head = search_reserve_window(fs_rsv_root, start_block);
+
+ /*
+ * find_next_reservable_window() simply finds a reservable window
+ * inside the given range(start_block, group_end_block).
+ *
+ * To make sure the reservation window has a free bit inside it, we
+ * need to check the bitmap after we found a reservable window.
+ */
+retry:
+ ret = find_next_reservable_window(search_head, my_rsv, sb,
+ start_block, group_end_block);
+
+ if (ret == -1) {
+ if (!rsv_is_empty(&my_rsv->rsv_window))
+ rsv_window_remove(sb, my_rsv);
+ spin_unlock(rsv_lock);
+ return -1;
+ }
+
+ /*
+ * On success, find_next_reservable_window() returns the
+ * reservation window where there is a reservable space after it.
+ * Before we reserve this reservable space, we need
+ * to make sure there is at least a free block inside this region.
+ *
+ * searching the first free bit on the block bitmap and copy of
+ * last committed bitmap alternatively, until we found a allocatable
+ * block. Search start from the start block of the reservable space
+ * we just found.
+ */
+ spin_unlock(rsv_lock);
+ first_free_block = bitmap_search_next_usable_block(
+ my_rsv->rsv_start - group_first_block,
+ bitmap_bh, group_end_block - group_first_block + 1);
+
+ if (first_free_block < 0) {
+ /*
+ * no free block left on the bitmap, no point
+ * to reserve the space. return failed.
+ */
+ spin_lock(rsv_lock);
+ if (!rsv_is_empty(&my_rsv->rsv_window))
+ rsv_window_remove(sb, my_rsv);
+ spin_unlock(rsv_lock);
+ return -1; /* failed */
+ }
+
+ start_block = first_free_block + group_first_block;
+ /*
+ * check if the first free block is within the
+ * free space we just reserved
+ */
+ if (start_block >= my_rsv->rsv_start && start_block < my_rsv->rsv_end)
+ return 0; /* success */
+ /*
+ * if the first free bit we found is out of the reservable space
+ * continue search for next reservable space,
+ * start from where the free block is,
+ * we also shift the list head to where we stopped last time
+ */
+ search_head = my_rsv;
+ spin_lock(rsv_lock);
+ goto retry;
+}
+
+static void try_to_extend_reservation(struct ext3_reserve_window_node *my_rsv,
+ struct super_block *sb, int size)
+{
+ struct ext3_reserve_window_node *next_rsv;
+ struct rb_node *next;
+ spinlock_t *rsv_lock = &EXT3_SB(sb)->s_rsv_window_lock;
+
+ if (!spin_trylock(rsv_lock))
+ return;
+
+ next = rb_next(&my_rsv->rsv_node);
+
+ if (!next)
+ my_rsv->rsv_end += size;
+ else {
+ next_rsv = list_entry(next, struct ext3_reserve_window_node, rsv_node);
+
+ if ((next_rsv->rsv_start - my_rsv->rsv_end - 1) >= size)
+ my_rsv->rsv_end += size;
+ else
+ my_rsv->rsv_end = next_rsv->rsv_start - 1;
+ }
+ spin_unlock(rsv_lock);
+}
+
+/*
+ * This is the main function used to allocate a new block and its reservation
+ * window.
+ *
+ * Each time when a new block allocation is need, first try to allocate from
+ * its own reservation. If it does not have a reservation window, instead of
+ * looking for a free bit on bitmap first, then look up the reservation list to
+ * see if it is inside somebody else's reservation window, we try to allocate a
+ * reservation window for it starting from the goal first. Then do the block
+ * allocation within the reservation window.
+ *
+ * This will avoid keeping on searching the reservation list again and
+ * again when somebody is looking for a free block (without
+ * reservation), and there are lots of free blocks, but they are all
+ * being reserved.
+ *
+ * We use a sorted double linked list for the per-filesystem reservation list.
+ * The insert, remove and find a free space(non-reserved) operations for the
+ * sorted double linked list should be fast.
+ *
+ */
+static int
+ext3_try_to_allocate_with_rsv(struct super_block *sb, handle_t *handle,
+ unsigned int group, struct buffer_head *bitmap_bh,
+ int goal, struct ext3_reserve_window_node * my_rsv,
+ unsigned long *count, int *errp)
+{
+ unsigned long group_first_block;
+ int ret = 0;
+ int fatal;
+ unsigned long num = *count;
+
+ *errp = 0;
+
+ /*
+ * Make sure we use undo access for the bitmap, because it is critical
+ * that we do the frozen_data COW on bitmap buffers in all cases even
+ * if the buffer is in BJ_Forget state in the committing transaction.
+ */
+ BUFFER_TRACE(bitmap_bh, "get undo access for new block");
+ fatal = ext3_journal_get_undo_access(handle, bitmap_bh);