Btrfs: dummy extent buffers for tree mod log
The tree modification log needs two ways to create dummy extent buffers,
once by allocating a fresh one (to rebuild an old root) and once by
cloning an existing one (to make private rewind modifications) to it.
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 2fb52c2..3daed70 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3930,6 +3930,7 @@
eb->start = start;
eb->len = len;
eb->tree = tree;
+ eb->bflags = 0;
rwlock_init(&eb->lock);
atomic_set(&eb->write_locks, 0);
atomic_set(&eb->read_locks, 0);
@@ -3967,6 +3968,60 @@
return eb;
}
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
+{
+ unsigned long i;
+ struct page *p;
+ struct extent_buffer *new;
+ unsigned long num_pages = num_extent_pages(src->start, src->len);
+
+ new = __alloc_extent_buffer(NULL, src->start, src->len, GFP_ATOMIC);
+ if (new == NULL)
+ return NULL;
+
+ for (i = 0; i < num_pages; i++) {
+ p = alloc_page(GFP_ATOMIC);
+ BUG_ON(!p);
+ attach_extent_buffer_page(new, p);
+ WARN_ON(PageDirty(p));
+ SetPageUptodate(p);
+ new->pages[i] = p;
+ }
+
+ copy_extent_buffer(new, src, 0, 0, src->len);
+ set_bit(EXTENT_BUFFER_UPTODATE, &new->bflags);
+ set_bit(EXTENT_BUFFER_DUMMY, &new->bflags);
+
+ return new;
+}
+
+struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len)
+{
+ struct extent_buffer *eb;
+ unsigned long num_pages = num_extent_pages(0, len);
+ unsigned long i;
+
+ eb = __alloc_extent_buffer(NULL, start, len, GFP_ATOMIC);
+ if (!eb)
+ return NULL;
+
+ for (i = 0; i < num_pages; i++) {
+ eb->pages[i] = alloc_page(GFP_ATOMIC);
+ if (!eb->pages[i])
+ goto err;
+ }
+ set_extent_buffer_uptodate(eb);
+ btrfs_set_header_nritems(eb, 0);
+ set_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
+
+ return eb;
+err:
+ for (i--; i > 0; i--)
+ __free_page(eb->pages[i]);
+ __free_extent_buffer(eb);
+ return NULL;
+}
+
static int extent_buffer_under_io(struct extent_buffer *eb)
{
return (atomic_read(&eb->io_pages) ||
@@ -3982,6 +4037,7 @@
{
unsigned long index;
struct page *page;
+ int mapped = !test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags);
BUG_ON(extent_buffer_under_io(eb));
@@ -3992,7 +4048,7 @@
do {
index--;
page = extent_buffer_page(eb, index);
- if (page) {
+ if (page && mapped) {
spin_lock(&page->mapping->private_lock);
/*
* We do this since we'll remove the pages after we've
@@ -4017,6 +4073,8 @@
}
spin_unlock(&page->mapping->private_lock);
+ }
+ if (page) {
/* One for when we alloced the page */
page_cache_release(page);
}
@@ -4235,14 +4293,18 @@
{
WARN_ON(atomic_read(&eb->refs) == 0);
if (atomic_dec_and_test(&eb->refs)) {
- struct extent_io_tree *tree = eb->tree;
+ if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
+ spin_unlock(&eb->refs_lock);
+ } else {
+ struct extent_io_tree *tree = eb->tree;
- spin_unlock(&eb->refs_lock);
+ spin_unlock(&eb->refs_lock);
- spin_lock(&tree->buffer_lock);
- radix_tree_delete(&tree->buffer,
- eb->start >> PAGE_CACHE_SHIFT);
- spin_unlock(&tree->buffer_lock);
+ spin_lock(&tree->buffer_lock);
+ radix_tree_delete(&tree->buffer,
+ eb->start >> PAGE_CACHE_SHIFT);
+ spin_unlock(&tree->buffer_lock);
+ }
/* Should be safe to release our pages at this point */
btrfs_release_extent_buffer_page(eb, 0);
@@ -4260,6 +4322,10 @@
spin_lock(&eb->refs_lock);
if (atomic_read(&eb->refs) == 2 &&
+ test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags))
+ atomic_dec(&eb->refs);
+
+ if (atomic_read(&eb->refs) == 2 &&
test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
!extent_buffer_under_io(eb) &&
test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))