btrfs-progs: docs: extra notes about read-only scrub on read-write fs

Documentation/btrfs-scrub.rst

@@ -89,6 +89,12 @@ start [-BdrRf] <path>|<device>
         -r
                 run in read-only mode, do not attempt to correct anything, can
                 be run on a read-only filesystem
+
+		Note that a read-only scrub on a read-write filesystem can
+		still cause write into the filesystem due to some internal
+		limitations.
+		Only a read-only scrub on a read-only fs can avoid writes from
+		scrub.
         -R
                 raw print mode, print full data instead of summary
         -f

Documentation/ch-scrub-intro.rst

@@ -46,6 +46,16 @@ read-write mounted filesystem.
    used, with expert guidance, to rebuild certain corrupted filesystem structures
    in the absence of any good replica.
 
+.. note::
+   Read-only scrub on read-write filesystem will cause some write into the
+   filesystem.
+
+   This is due to the design limitation to prevent race between marking block
+   group read-only and writing back block group items.
+
+   To avoid any writes from scrub, one has to run read-only scrub on read-only
+   filesystem.
+
 The user is supposed to run it manually or via a periodic system service. The
 recommended period is a month but it could be less. The estimated device bandwidth
 utilization is about 80% on an idle filesystem.

Documentation/mkfs.btrfs.rst

@@ -212,6 +212,15 @@ OPTIONS
 
                 $ mkfs.btrfs -O list-all
 
+--compress <algo>[:<level>]
+        Try to compress files when using *--rootdir*.  Supported values for *algo* are
+        *no* (the default), *zlib*, *lzo*, and *zstd*.  The optional value *level* is a
+        compression level, from 1 to 9 for ZLIB and from 1 to 15 for ZSTD.
+
+        As with the kernel, :command:`mkfs.btrfs` won't write compressed extents when
+        they would be larger than the uncompressed versions, and will mark a file as
+        `nocompress` if its beginning is found to be incompressible.
+
 -f|--force
         Forcibly overwrite the block devices when an existing filesystem is detected.
         By default, :command:`mkfs.btrfs` will utilize *libblkid* to check for any known

Makefile

@@ -740,11 +740,11 @@ btrfsck.static: btrfs.static
 
 mkfs.btrfs: $(mkfs_objects) $(objects) libbtrfsutil.a
 	@echo "    [LD]     $@"
-	$(Q)$(CC) -o $@ $^ $(LDFLAGS) $(LIBS)
+	$(Q)$(CC) -o $@ $^ $(LDFLAGS) $(LIBS) $(LIBS_COMP)
 
 mkfs.btrfs.static: $(static_mkfs_objects) $(static_objects) $(static_libbtrfs_objects)
 	@echo "    [LD]     $@"
-	$(Q)$(CC) -o $@ $^ $(STATIC_LDFLAGS) $(STATIC_LIBS)
+	$(Q)$(CC) -o $@ $^ $(STATIC_LDFLAGS) $(STATIC_LIBS) $(STATIC_LIBS_COMP)
 
 btrfstune: $(tune_objects) $(objects) libbtrfsutil.a
 	@echo "    [LD]     $@"

common/extent-tree-utils.c

@@ -15,18 +15,14 @@
  */
 
 #include "kerncompat.h"
-#include <errno.h>
 #include <stddef.h>
 #include "kernel-shared/accessors.h"
 #include "kernel-shared/uapi/btrfs_tree.h"
 #include "kernel-shared/ctree.h"
 #include "kernel-shared/disk-io.h"
-#include "kernel-shared/file-item.h"
-#include "kernel-shared/transaction.h"
 #include "kernel-shared/free-space-tree.h"
-#include "common/internal.h"
+#include "kernel-shared/transaction.h"
 #include "common/extent-tree-utils.h"
-#include "common/messages.h"
 
 /*
  * Search in extent tree to found next meta/data extent. Caller needs to check
@@ -50,238 +46,3 @@ int btrfs_next_extent_item(struct btrfs_root *root, struct btrfs_path *path,
 		return 0;
 	}
 }
-
-static void __get_extent_size(struct btrfs_root *root, struct btrfs_path *path,
-			      u64 *start, u64 *len)
-{
-	struct btrfs_key key;
-
-	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
-	BUG_ON(!(key.type == BTRFS_EXTENT_ITEM_KEY ||
-		 key.type == BTRFS_METADATA_ITEM_KEY));
-	*start = key.objectid;
-	if (key.type == BTRFS_EXTENT_ITEM_KEY)
-		*len = key.offset;
-	else
-		*len = root->fs_info->nodesize;
-}
-
-/*
- * Find first overlap extent for range [bytenr, bytenr + len).
- *
- * Return 0 for found and point path to it.
- * Return >0 for not found.
- * Return <0 for err
- */
-static int btrfs_search_overlap_extent(struct btrfs_root *root,
-				       struct btrfs_path *path, u64 bytenr, u64 len)
-{
-	struct btrfs_key key;
-	u64 cur_start;
-	u64 cur_len;
-	int ret;
-
-	key.objectid = bytenr;
-	key.type = BTRFS_EXTENT_DATA_KEY;
-	key.offset = (u64)-1;
-
-	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
-	if (ret < 0)
-		return ret;
-	if (ret == 0) {
-		error_msg(ERROR_MSG_UNEXPECTED, "EXTENT_DATA found at %llu", bytenr);
-		return -EUCLEAN;
-	}
-
-	ret = btrfs_previous_extent_item(root, path, 0);
-	if (ret < 0)
-		return ret;
-	/* No previous, check next extent. */
-	if (ret > 0)
-		goto next;
-	__get_extent_size(root, path, &cur_start, &cur_len);
-	/* Tail overlap. */
-	if (cur_start + cur_len > bytenr)
-		return 1;
-
-next:
-	ret = btrfs_next_extent_item(root, path, bytenr + len);
-	if (ret < 0)
-		return ret;
-	/* No next, prev already checked, no overlap. */
-	if (ret > 0)
-		return 0;
-	__get_extent_size(root, path, &cur_start, &cur_len);
-	/* Head overlap.*/
-	if (cur_start < bytenr + len)
-		return 1;
-	return 0;
-}
-
-static int __btrfs_record_file_extent(struct btrfs_trans_handle *trans,
-				      struct btrfs_root *root, u64 objectid,
-				      struct btrfs_inode_item *inode,
-				      u64 file_pos, u64 disk_bytenr,
-				      u64 *ret_num_bytes)
-{
-	int ret;
-	struct btrfs_fs_info *info = root->fs_info;
-	struct btrfs_root *extent_root = btrfs_extent_root(info, disk_bytenr);
-	struct extent_buffer *leaf;
-	struct btrfs_file_extent_item *fi;
-	struct btrfs_key ins_key;
-	struct btrfs_path *path;
-	struct btrfs_extent_item *ei;
-	u64 nbytes;
-	u64 extent_num_bytes;
-	u64 extent_bytenr;
-	u64 extent_offset;
-	u64 num_bytes = *ret_num_bytes;
-
-	/*
-	 * @objectid should be an inode number, thus it must not be smaller
-	 * than BTRFS_FIRST_FREE_OBJECTID.
-	 */
-	UASSERT(objectid >= BTRFS_FIRST_FREE_OBJECTID);
-
-	/*
-	 * All supported file system should not use its 0 extent.  As it's for
-	 * hole.  And hole extent has no size limit, no need to loop.
-	 */
-	if (disk_bytenr == 0) {
-		ret = btrfs_insert_file_extent(trans, root, objectid,
-					       file_pos, disk_bytenr,
-					       num_bytes, num_bytes);
-		return ret;
-	}
-	num_bytes = min_t(u64, num_bytes, BTRFS_MAX_EXTENT_SIZE);
-
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
-	/* First to check extent overlap. */
-	ret = btrfs_search_overlap_extent(extent_root, path, disk_bytenr, num_bytes);
-	if (ret < 0)
-		goto fail;
-	if (ret > 0) {
-		/* Found overlap. */
-		u64 cur_start;
-		u64 cur_len;
-
-		__get_extent_size(extent_root, path, &cur_start, &cur_len);
-		/* For convert case, this extent should be a subset of existing one. */
-		if (disk_bytenr < cur_start) {
-			error_msg(ERROR_MSG_UNEXPECTED,
-				  "invalid range disk_bytenr < cur_start: %llu < %llu",
-				  disk_bytenr, cur_start);
-			ret = -EUCLEAN;
-			goto fail;
-		}
-
-		extent_bytenr = cur_start;
-		extent_num_bytes = cur_len;
-		extent_offset = disk_bytenr - extent_bytenr;
-	} else {
-		/* No overlap, create new extent. */
-		btrfs_release_path(path);
-		ins_key.objectid = disk_bytenr;
-		ins_key.type = BTRFS_EXTENT_ITEM_KEY;
-		ins_key.offset = num_bytes;
-
-		ret = btrfs_insert_empty_item(trans, extent_root, path,
-					      &ins_key, sizeof(*ei));
-		if (ret == 0) {
-			leaf = path->nodes[0];
-			ei = btrfs_item_ptr(leaf, path->slots[0],
-					    struct btrfs_extent_item);
-
-			btrfs_set_extent_refs(leaf, ei, 0);
-			btrfs_set_extent_generation(leaf, ei, trans->transid);
-			btrfs_set_extent_flags(leaf, ei,
-					       BTRFS_EXTENT_FLAG_DATA);
-			btrfs_mark_buffer_dirty(leaf);
-
-			ret = btrfs_update_block_group(trans, disk_bytenr,
-						       num_bytes, 1, 0);
-			if (ret)
-				goto fail;
-		} else if (ret != -EEXIST) {
-			goto fail;
-		}
-
-		ret = remove_from_free_space_tree(trans, disk_bytenr, num_bytes);
-		if (ret)
-			goto fail;
-
-		btrfs_run_delayed_refs(trans, -1);
-		extent_bytenr = disk_bytenr;
-		extent_num_bytes = num_bytes;
-		extent_offset = 0;
-	}
-	btrfs_release_path(path);
-	ins_key.objectid = objectid;
-	ins_key.type = BTRFS_EXTENT_DATA_KEY;
-	ins_key.offset = file_pos;
-	ret = btrfs_insert_empty_item(trans, root, path, &ins_key, sizeof(*fi));
-	if (ret)
-		goto fail;
-	leaf = path->nodes[0];
-	fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
-	btrfs_set_file_extent_generation(leaf, fi, trans->transid);
-	btrfs_set_file_extent_type(leaf, fi, BTRFS_FILE_EXTENT_REG);
-	btrfs_set_file_extent_disk_bytenr(leaf, fi, extent_bytenr);
-	btrfs_set_file_extent_disk_num_bytes(leaf, fi, extent_num_bytes);
-	btrfs_set_file_extent_offset(leaf, fi, extent_offset);
-	btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes);
-	btrfs_set_file_extent_ram_bytes(leaf, fi, extent_num_bytes);
-	btrfs_set_file_extent_compression(leaf, fi, 0);
-	btrfs_set_file_extent_encryption(leaf, fi, 0);
-	btrfs_set_file_extent_other_encoding(leaf, fi, 0);
-	btrfs_mark_buffer_dirty(leaf);
-
-	nbytes = btrfs_stack_inode_nbytes(inode) + num_bytes;
-	btrfs_set_stack_inode_nbytes(inode, nbytes);
-	btrfs_release_path(path);
-
-	ret = btrfs_inc_extent_ref(trans, extent_bytenr, extent_num_bytes,
-				   0, root->root_key.objectid, objectid,
-				   file_pos - extent_offset);
-	if (ret)
-		goto fail;
-	ret = 0;
-	*ret_num_bytes = min(extent_num_bytes - extent_offset, num_bytes);
-fail:
-	btrfs_free_path(path);
-	return ret;
-}
-
-/*
- * Record a file extent. Do all the required works, such as inserting file
- * extent item, inserting extent item and backref item into extent tree and
- * updating block accounting.
- */
-int btrfs_record_file_extent(struct btrfs_trans_handle *trans,
-			     struct btrfs_root *root, u64 objectid,
-			     struct btrfs_inode_item *inode,
-			     u64 file_pos, u64 disk_bytenr,
-			     u64 num_bytes)
-{
-	u64 cur_disk_bytenr = disk_bytenr;
-	u64 cur_file_pos = file_pos;
-	u64 cur_num_bytes = num_bytes;
-	int ret = 0;
-
-	while (num_bytes > 0) {
-		ret = __btrfs_record_file_extent(trans, root, objectid,
-						 inode, cur_file_pos,
-						 cur_disk_bytenr,
-						 &cur_num_bytes);
-		if (ret < 0)
-			break;
-		cur_disk_bytenr += cur_num_bytes;
-		cur_file_pos += cur_num_bytes;
-		num_bytes -= cur_num_bytes;
-	}
-	return ret;
-}

common/extent-tree-utils.h

@@ -19,6 +19,7 @@
 
 #include "kerncompat.h"
 #include "kernel-lib/bitops.h"
+#include "kernel-shared/compression.h"
 
 struct btrfs_inode_item;
 struct btrfs_path;
@@ -27,10 +28,5 @@ struct btrfs_trans_handle;
 
 int btrfs_next_extent_item(struct btrfs_root *root, struct btrfs_path *path,
 			   u64 max_objectid);
-int btrfs_record_file_extent(struct btrfs_trans_handle *trans,
-			     struct btrfs_root *root, u64 objectid,
-			     struct btrfs_inode_item *inode,
-			     u64 file_pos, u64 disk_bytenr,
-			     u64 num_bytes);
 
 #endif