btrfs: improve comments around nocow path (a6bd9cd1) · Commits · 戴 / test

fs/btrfs/extent-tree.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -2357,16 +2357,19 @@ static noinline int check_committed_ref(struct btrfs_root *root,
		item_size = btrfs_item_size_nr(leaf, path->slots[0]);
		ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);

		/* If extent item has more than 1 inline ref then it's shared */
		if (item_size != sizeof(*ei) +
		btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY))
		goto out;

		/* If extent created before last snapshot => it's definitely shared */
		if (btrfs_extent_generation(leaf, ei) <=
		btrfs_root_last_snapshot(&root->root_item))
		goto out;

		iref = (struct btrfs_extent_inline_ref *)(ei + 1);

		/* If this extent has SHARED_DATA_REF then it's shared */
		type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_DATA);
		if (type != BTRFS_EXTENT_DATA_REF_KEY)
		goto out;

fs/btrfs/inode.c

+47 −4

Original line number	Diff line number	Diff line
		@@ -1345,6 +1345,12 @@ static noinline int run_delalloc_nocow(struct inode *inode,
		cur_offset, 0);
		if (ret < 0)
		goto error;

		/*
		* If there is no extent for our range when doing the initial
		* search, then go back to the previous slot as it will be the
		* one containing the search offset
		*/
		if (ret > 0 && path->slots[0] > 0 && check_prev) {
		leaf = path->nodes[0];
		btrfs_item_key_to_cpu(leaf, &found_key,
		@@ -1355,6 +1361,7 @@ static noinline int run_delalloc_nocow(struct inode *inode,
		}
		check_prev = false;
		next_slot:
		/* Go to next leaf if we have exhausted the current one */
		leaf = path->nodes[0];
		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
		ret = btrfs_next_leaf(root, path);
		@@ -1370,23 +1377,38 @@ next_slot:

		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);

		/* Didn't find anything for our INO */
		if (found_key.objectid > ino)
		break;
		/*
		* Keep searching until we find an EXTENT_ITEM or there are no
		* more extents for this inode
		*/
		if (WARN_ON_ONCE(found_key.objectid < ino) \|\|
		found_key.type < BTRFS_EXTENT_DATA_KEY) {
		path->slots[0]++;
		goto next_slot;
		}

		/* Found key is not EXTENT_DATA_KEY or starts after req range */
		if (found_key.type > BTRFS_EXTENT_DATA_KEY \|\|
		found_key.offset > end)
		break;

		/*
		* If the found extent starts after requested offset, then
		* adjust extent_end to be right before this extent begins
		*/
		if (found_key.offset > cur_offset) {
		extent_end = found_key.offset;
		extent_type = 0;
		goto out_check;
		}

		/*
		* Found extent which begins before our range and potentially
		* intersect it
		*/
		fi = btrfs_item_ptr(leaf, path->slots[0],
		struct btrfs_file_extent_item);
		extent_type = btrfs_file_extent_type(leaf, fi);
		@@ -1400,19 +1422,28 @@ next_slot:
		btrfs_file_extent_num_bytes(leaf, fi);
		disk_num_bytes =
		btrfs_file_extent_disk_num_bytes(leaf, fi);
		/*
		* If extent we got ends before our range starts, skip
		* to next extent
		*/
		if (extent_end <= start) {
		path->slots[0]++;
		goto next_slot;
		}
		/* Skip holes */
		if (disk_bytenr == 0)
		goto out_check;
		/* Skip compressed/encrypted/encoded extents */
		if (btrfs_file_extent_compression(leaf, fi) \|\|
		btrfs_file_extent_encryption(leaf, fi) \|\|
		btrfs_file_extent_other_encoding(leaf, fi))
		goto out_check;
		/*
		* Do the same check as in btrfs_cross_ref_exist but
		* without the unnecessary search.
		* If extent is created before the last volume's snapshot
		* this implies the extent is shared, hence we can't do
		* nocow. This is the same check as in
		* btrfs_cross_ref_exist but without calling
		* btrfs_search_slot.
		*/
		if (!freespace_inode &&
		btrfs_file_extent_generation(leaf, fi) <=
		@@ -1420,6 +1451,7 @@ next_slot:
		goto out_check;
		if (extent_type == BTRFS_FILE_EXTENT_REG && !force)
		goto out_check;
		/* If extent is RO, we must COW it */
		if (btrfs_extent_readonly(fs_info, disk_bytenr))
		goto out_check;
		ret = btrfs_cross_ref_exist(root, ino,
		@@ -1443,8 +1475,8 @@ next_slot:
		disk_bytenr += cur_offset - found_key.offset;
		num_bytes = min(end + 1, extent_end) - cur_offset;
		/*
		* if there are pending snapshots for this root,
		* we fall into common COW way.
		* If there are pending snapshots for this root, we
		* fall into common COW way
		*/
		if (!freespace_inode && atomic_read(&root->snapshot_force_cow))
		goto out_check;
		@@ -1480,12 +1512,17 @@ next_slot:
		BUG();
		}
		out_check:
		/* Skip extents outside of our requested range */
		if (extent_end <= start) {
		path->slots[0]++;
		if (nocow)
		btrfs_dec_nocow_writers(fs_info, disk_bytenr);
		goto next_slot;
		}
		/*
		* If nocow is false then record the beginning of the range
		* that needs to be COWed
		*/
		if (!nocow) {
		if (cow_start == (u64)-1)
		cow_start = cur_offset;
		@@ -1497,6 +1534,12 @@ out_check:
		}

		btrfs_release_path(path);

		/*
		* COW range from cow_start to found_key.offset - 1. As the key
		* will contain the beginning of the first extent that can be
		* NOCOW, following one which needs to be COW'ed
		*/
		if (cow_start != (u64)-1) {
		ret = cow_file_range(inode, locked_page,
		cow_start, found_key.offset - 1,

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