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 2fb52c26c677d22867cbe96e46e230813fe03053..3daed70a401abe7d5cc8b0bdaee4a976a2a2760a 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3930,6 +3930,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
        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 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
        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 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
 {
        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 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
        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 @@ static void btrfs_release_extent_buffer_page(struct extent_buffer *eb,
                        }
                        spin_unlock(&page->mapping->private_lock);
 
+               }
+               if (page) {
                        /* One for when we alloced the page */
                        page_cache_release(page);
                }
@@ -4235,14 +4293,18 @@ static void release_extent_buffer(struct extent_buffer *eb, gfp_t mask)
 {
        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);
@@ -4259,6 +4321,10 @@ void free_extent_buffer(struct extent_buffer *eb)
                return;
 
        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) &&

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index b516c3b8dec68d825e380a1930976f34c8a3e1a4..96434a61d7c2a41e1aa580c8a3dccf7f923f7c58 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -39,6 +39,7 @@
 #define EXTENT_BUFFER_STALE 6
 #define EXTENT_BUFFER_WRITEBACK 7
 #define EXTENT_BUFFER_IOERR 8
+#define EXTENT_BUFFER_DUMMY 9
 
 /* these are flags for extent_clear_unlock_delalloc */
 #define EXTENT_CLEAR_UNLOCK_PAGE 0x1
@@ -265,6 +266,8 @@ void set_page_extent_mapped(struct page *page);
 
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                                          u64 start, unsigned long len);
+struct extent_buffer *alloc_dummy_extent_buffer(u64 start, unsigned long len);
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
 struct extent_buffer *find_extent_buffer(struct extent_io_tree *tree,
                                         u64 start, unsigned long len);
 void free_extent_buffer(struct extent_buffer *eb);