Btrfs: add support for inode properties

This change adds infrastructure to allow for generic properties for
inodes. Properties are name/value pairs that can be associated with
inodes for different purposes. They are stored as xattrs with the
prefix "btrfs."

Properties can be inherited - this means when a directory inode has
inheritable properties set, these are added to new inodes created
under that directory. Further, subvolumes can also have properties
associated with them, and they can be inherited from their parent
subvolume. Naturally, directory properties have priority over subvolume
properties (in practice a subvolume property is just a regular
property associated with the root inode, objectid 256, of the
subvolume's fs tree).

This change also adds one specific property implementation, named
"compression", whose values can be "lzo" or "zlib" and it's an
inheritable property.

The corresponding changes to btrfs-progs were also implemented.
A patch with xfstests for this feature will follow once there's
agreement on this change/feature.

Further, the script at the bottom of this commit message was used to
do some benchmarks to measure any performance penalties of this feature.

Basically the tests correspond to:

Test 1 - create a filesystem and mount it with compress-force=lzo,
then sequentially create N files of 64Kb each, measure how long it took
to create the files, unmount the filesystem, mount the filesystem and
perform an 'ls -lha' against the test directory holding the N files, and
report the time the command took.

Test 2 - create a filesystem and don't use any compression option when
mounting it - instead set the compression property of the subvolume's
root to 'lzo'. Then create N files of 64Kb, and report the time it took.
The unmount the filesystem, mount it again and perform an 'ls -lha' like
in the former test. This means every single file ends up with a property
(xattr) associated to it.

Test 3 - same as test 2, but uses 4 properties - 3 are duplicates of the
compression property, have no real effect other than adding more work
when inheriting properties and taking more btree leaf space.

Test 4 - same as test 3 but with 10 properties per file.

Results (in seconds, and averages of 5 runs each), for different N
numbers of files follow.

* Without properties (test 1)

                    file creation time        ls -lha time
10 000 files              3.49                   0.76
100 000 files            47.19                   8.37
1 000 000 files         518.51                 107.06

* With 1 property (compression property set to lzo - test 2)

                    file creation time        ls -lha time
10 000 files              3.63                    0.93
100 000 files            48.56                    9.74
1 000 000 files         537.72                  125.11

* With 4 properties (test 3)

                    file creation time        ls -lha time
10 000 files              3.94                    1.20
100 000 files            52.14                   11.48
1 000 000 files         572.70                  142.13

* With 10 properties (test 4)

                    file creation time        ls -lha time
10 000 files              4.61                    1.35
100 000 files            58.86                   13.83
1 000 000 files         656.01                  177.61

The increased latencies with properties are essencialy because of:

*) When creating an inode, we now synchronously write 1 more item
   (an xattr item) for each property inherited from the parent dir
   (or subvolume). This could be done in an asynchronous way such
   as we do for dir intex items (delayed-inode.c), which could help
   reduce the file creation latency;

*) With properties, we now have larger fs trees. For this particular
   test each xattr item uses 75 bytes of leaf space in the fs tree.
   This could be less by using a new item for xattr items, instead of
   the current btrfs_dir_item, since we could cut the 'location' and
   'type' fields (saving 18 bytes) and maybe 'transid' too (saving a
   total of 26 bytes per xattr item) from the btrfs_dir_item type.

Also tried batching the xattr insertions (ignoring proper hash
collision handling, since it didn't exist) when creating files that
inherit properties from their parent inode/subvolume, but the end
results were (surprisingly) essentially the same.

Test script:

$ cat test.pl
  #!/usr/bin/perl -w

  use strict;
  use Time::HiRes qw(time);
  use constant NUM_FILES => 10_000;
  use constant FILE_SIZES => (64 * 1024);
  use constant DEV => '/dev/sdb4';
  use constant MNT_POINT => '/home/fdmanana/btrfs-tests/dev';
  use constant TEST_DIR => (MNT_POINT . '/testdir');

  system("mkfs.btrfs", "-l", "16384", "-f", DEV) == 0 or die "mkfs.btrfs failed!";

  # following line for testing without properties
  #system("mount", "-o", "compress-force=lzo", DEV, MNT_POINT) == 0 or die "mount failed!";

  # following 2 lines for testing with properties
  system("mount", DEV, MNT_POINT) == 0 or die "mount failed!";
  system("btrfs", "prop", "set", MNT_POINT, "compression", "lzo") == 0 or die "set prop failed!";

  system("mkdir", TEST_DIR) == 0 or die "mkdir failed!";
  my ($t1, $t2);

  $t1 = time();
  for (my $i = 1; $i <= NUM_FILES; $i++) {
      my $p = TEST_DIR . '/file_' . $i;
      open(my $f, '>', $p) or die "Error opening file!";
      $f->autoflush(1);
      for (my $j = 0; $j < FILE_SIZES; $j += 4096) {
          print $f ('A' x 4096) or die "Error writing to file!";
      }
      close($f);
  }
  $t2 = time();
  print "Time to create " . NUM_FILES . ": " . ($t2 - $t1) . " seconds.\n";
  system("umount", DEV) == 0 or die "umount failed!";
  system("mount", DEV, MNT_POINT) == 0 or die "mount failed!";

  $t1 = time();
  system("bash -c 'ls -lha " . TEST_DIR . " > /dev/null'") == 0 or die "ls failed!";
  $t2 = time();
  print "Time to ls -lha all files: " . ($t2 - $t1) . " seconds.\n";
  system("umount", DEV) == 0 or die "umount failed!";

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/Makefile

@@ -9,7 +9,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
 	   export.o tree-log.o free-space-cache.o zlib.o lzo.o \
 	   compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \
 	   reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
-	   uuid-tree.o
+	   uuid-tree.o props.o
 
 btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
 btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o

fs/btrfs/btrfs_inode.h

@@ -43,6 +43,7 @@
 #define BTRFS_INODE_COPY_EVERYTHING		8
 #define BTRFS_INODE_IN_DELALLOC_LIST		9
 #define BTRFS_INODE_READDIO_NEED_LOCK		10
+#define BTRFS_INODE_HAS_PROPS		        11
 
 /* in memory btrfs inode */
 struct btrfs_inode {

fs/btrfs/ctree.h

@@ -3703,7 +3703,9 @@ int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, int delay_iput);
 int btrfs_set_extent_delalloc(struct inode *inode, u64 start, u64 end,
 			      struct extent_state **cached_state);
 int btrfs_create_subvol_root(struct btrfs_trans_handle *trans,
-			     struct btrfs_root *new_root, u64 new_dirid);
+			     struct btrfs_root *new_root,
+			     struct btrfs_root *parent_root,
+			     u64 new_dirid);
 int btrfs_merge_bio_hook(int rw, struct page *page, unsigned long offset,
 			 size_t size, struct bio *bio,
 			 unsigned long bio_flags);

fs/btrfs/inode.c

@@ -58,6 +58,7 @@
 #include "inode-map.h"
 #include "backref.h"
 #include "hash.h"
+#include "props.h"
 
 struct btrfs_iget_args {
 	u64 ino;
@@ -3265,7 +3266,8 @@ int btrfs_orphan_cleanup(struct btrfs_root *root)
  * slot is the slot the inode is in, objectid is the objectid of the inode
  */
 static noinline int acls_after_inode_item(struct extent_buffer *leaf,
-					  int slot, u64 objectid)
+					  int slot, u64 objectid,
+					  int *first_xattr_slot)
 {
 	u32 nritems = btrfs_header_nritems(leaf);
 	struct btrfs_key found_key;
@@ -3281,6 +3283,7 @@ static noinline int acls_after_inode_item(struct extent_buffer *leaf,
 	}
 
 	slot++;
+	*first_xattr_slot = -1;
 	while (slot < nritems) {
 		btrfs_item_key_to_cpu(leaf, &found_key, slot);
 
@@ -3290,6 +3293,8 @@ static noinline int acls_after_inode_item(struct extent_buffer *leaf,
 
 		/* we found an xattr, assume we've got an acl */
 		if (found_key.type == BTRFS_XATTR_ITEM_KEY) {
+			if (*first_xattr_slot == -1)
+				*first_xattr_slot = slot;
 			if (found_key.offset == xattr_access ||
 			    found_key.offset == xattr_default)
 				return 1;
@@ -3318,6 +3323,8 @@ static noinline int acls_after_inode_item(struct extent_buffer *leaf,
 	 * something larger than an xattr.  We have to assume the inode
 	 * has acls
 	 */
+	if (*first_xattr_slot == -1)
+		*first_xattr_slot = slot;
 	return 1;
 }
 
@@ -3337,6 +3344,7 @@ static void btrfs_read_locked_inode(struct inode *inode)
 	u32 rdev;
 	int ret;
 	bool filled = false;
+	int first_xattr_slot;
 
 	ret = btrfs_fill_inode(inode, &rdev);
 	if (!ret)
@@ -3346,7 +3354,6 @@ static void btrfs_read_locked_inode(struct inode *inode)
 	if (!path)
 		goto make_bad;
 
-	path->leave_spinning = 1;
 	memcpy(&location, &BTRFS_I(inode)->location, sizeof(location));
 
 	ret = btrfs_lookup_inode(NULL, root, path, &location, 0);
@@ -3429,12 +3436,21 @@ static void btrfs_read_locked_inode(struct inode *inode)
 	 * any xattrs or acls
 	 */
 	maybe_acls = acls_after_inode_item(leaf, path->slots[0],
-					   btrfs_ino(inode));
+					   btrfs_ino(inode), &first_xattr_slot);
+	if (first_xattr_slot != -1) {
+		path->slots[0] = first_xattr_slot;
+		ret = btrfs_load_inode_props(inode, path);
+		if (ret)
+			btrfs_err(root->fs_info,
+				  "error loading props for ino %llu (root %llu): %d\n",
+				  btrfs_ino(inode),
+				  root->root_key.objectid, ret);
+	}
+	btrfs_free_path(path);
+
 	if (!maybe_acls)
 		cache_no_acl(inode);
 
-	btrfs_free_path(path);
-
 	switch (inode->i_mode & S_IFMT) {
 	case S_IFREG:
 		inode->i_mapping->a_ops = &btrfs_aops;
@@ -5607,6 +5623,12 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
 
 	btrfs_update_root_times(trans, root);
 
+	ret = btrfs_inode_inherit_props(trans, inode, dir);
+	if (ret)
+		btrfs_err(root->fs_info,
+			  "error inheriting props for ino %llu (root %llu): %d",
+			  btrfs_ino(inode), root->root_key.objectid, ret);
+
 	return inode;
 fail:
 	if (dir)
@@ -7889,7 +7911,9 @@ static int btrfs_truncate(struct inode *inode)
  * create a new subvolume directory/inode (helper for the ioctl).
  */
 int btrfs_create_subvol_root(struct btrfs_trans_handle *trans,
-			     struct btrfs_root *new_root, u64 new_dirid)
+			     struct btrfs_root *new_root,
+			     struct btrfs_root *parent_root,
+			     u64 new_dirid)
 {
 	struct inode *inode;
 	int err;
@@ -7907,6 +7931,12 @@ int btrfs_create_subvol_root(struct btrfs_trans_handle *trans,
 	set_nlink(inode, 1);
 	btrfs_i_size_write(inode, 0);
 
+	err = btrfs_subvol_inherit_props(trans, new_root, parent_root);
+	if (err)
+		btrfs_err(new_root->fs_info,
+			  "error inheriting subvolume %llu properties: %d\n",
+			  new_root->root_key.objectid, err);
+
 	err = btrfs_update_inode(trans, new_root, inode);
 
 	iput(inode);

fs/btrfs/ioctl.c

@@ -56,6 +56,7 @@
 #include "rcu-string.h"
 #include "send.h"
 #include "dev-replace.h"
+#include "props.h"
 #include "sysfs.h"
 
 static int btrfs_clone(struct inode *src, struct inode *inode,
@@ -281,9 +282,25 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	if (flags & FS_NOCOMP_FL) {
 		ip->flags &= ~BTRFS_INODE_COMPRESS;
 		ip->flags |= BTRFS_INODE_NOCOMPRESS;
+
+		ret = btrfs_set_prop(inode, "btrfs.compression", NULL, 0, 0);
+		if (ret && ret != -ENODATA)
+			goto out_drop;
 	} else if (flags & FS_COMPR_FL) {
+		const char *comp;
+
 		ip->flags |= BTRFS_INODE_COMPRESS;
 		ip->flags &= ~BTRFS_INODE_NOCOMPRESS;
+
+		if (root->fs_info->compress_type == BTRFS_COMPRESS_LZO)
+			comp = "lzo";
+		else
+			comp = "zlib";
+		ret = btrfs_set_prop(inode, "btrfs.compression",
+				     comp, strlen(comp), 0);
+		if (ret)
+			goto out_drop;
+
 	} else {
 		ip->flags &= ~(BTRFS_INODE_COMPRESS | BTRFS_INODE_NOCOMPRESS);
 	}
@@ -502,7 +519,7 @@ static noinline int create_subvol(struct inode *dir,
 
 	btrfs_record_root_in_trans(trans, new_root);
 
-	ret = btrfs_create_subvol_root(trans, new_root, new_dirid);
+	ret = btrfs_create_subvol_root(trans, new_root, root, new_dirid);
 	if (ret) {
 		/* We potentially lose an unused inode item here */
 		btrfs_abort_transaction(trans, root, ret);

fs/btrfs/props.c

@@ -0,0 +1,427 @@
+/*
+ * Copyright (C) 2014 Filipe David Borba Manana <fdmanana@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/hashtable.h>
+#include "props.h"
+#include "btrfs_inode.h"
+#include "hash.h"
+#include "transaction.h"
+#include "xattr.h"
+
+#define BTRFS_PROP_HANDLERS_HT_BITS 8
+static DEFINE_HASHTABLE(prop_handlers_ht, BTRFS_PROP_HANDLERS_HT_BITS);
+
+struct prop_handler {
+	struct hlist_node node;
+	const char *xattr_name;
+	int (*validate)(const char *value, size_t len);
+	int (*apply)(struct inode *inode, const char *value, size_t len);
+	const char *(*extract)(struct inode *inode);
+	int inheritable;
+};
+
+static int prop_compression_validate(const char *value, size_t len);
+static int prop_compression_apply(struct inode *inode,
+				  const char *value,
+				  size_t len);
+static const char *prop_compression_extract(struct inode *inode);
+
+static struct prop_handler prop_handlers[] = {
+	{
+		.xattr_name = XATTR_BTRFS_PREFIX "compression",
+		.validate = prop_compression_validate,
+		.apply = prop_compression_apply,
+		.extract = prop_compression_extract,
+		.inheritable = 1
+	},
+	{
+		.xattr_name = NULL
+	}
+};
+
+void __init btrfs_props_init(void)
+{
+	struct prop_handler *p;
+
+	hash_init(prop_handlers_ht);
+
+	for (p = &prop_handlers[0]; p->xattr_name; p++) {
+		u64 h = btrfs_name_hash(p->xattr_name, strlen(p->xattr_name));
+
+		hash_add(prop_handlers_ht, &p->node, h);
+	}
+}
+
+static const struct hlist_head *find_prop_handlers_by_hash(const u64 hash)
+{
+	struct hlist_head *h;
+
+	h = &prop_handlers_ht[hash_min(hash, BTRFS_PROP_HANDLERS_HT_BITS)];
+	if (hlist_empty(h))
+		return NULL;
+
+	return h;
+}
+
+static const struct prop_handler *
+find_prop_handler(const char *name,
+		  const struct hlist_head *handlers)
+{
+	struct prop_handler *h;
+
+	if (!handlers) {
+		u64 hash = btrfs_name_hash(name, strlen(name));
+
+		handlers = find_prop_handlers_by_hash(hash);
+		if (!handlers)
+			return NULL;
+	}
+
+	hlist_for_each_entry(h, handlers, node)
+		if (!strcmp(h->xattr_name, name))
+			return h;
+
+	return NULL;
+}
+
+static int __btrfs_set_prop(struct btrfs_trans_handle *trans,
+			    struct inode *inode,
+			    const char *name,
+			    const char *value,
+			    size_t value_len,
+			    int flags)
+{
+	const struct prop_handler *handler;
+	int ret;
+
+	if (strlen(name) <= XATTR_BTRFS_PREFIX_LEN)
+		return -EINVAL;
+
+	handler = find_prop_handler(name, NULL);
+	if (!handler)
+		return -EINVAL;
+
+	if (value_len == 0) {
+		ret = __btrfs_setxattr(trans, inode, handler->xattr_name,
+				       NULL, 0, flags);
+		if (ret)
+			return ret;
+
+		ret = handler->apply(inode, NULL, 0);
+		ASSERT(ret == 0);
+
+		return ret;
+	}
+
+	ret = handler->validate(value, value_len);
+	if (ret)
+		return ret;
+	ret = __btrfs_setxattr(trans, inode, handler->xattr_name,
+			       value, value_len, flags);
+	if (ret)
+		return ret;
+	ret = handler->apply(inode, value, value_len);
+	if (ret) {
+		__btrfs_setxattr(trans, inode, handler->xattr_name,
+				 NULL, 0, flags);
+		return ret;
+	}
+
+	set_bit(BTRFS_INODE_HAS_PROPS, &BTRFS_I(inode)->runtime_flags);
+
+	return 0;
+}
+
+int btrfs_set_prop(struct inode *inode,
+		   const char *name,
+		   const char *value,
+		   size_t value_len,
+		   int flags)
+{
+	return __btrfs_set_prop(NULL, inode, name, value, value_len, flags);
+}
+
+static int iterate_object_props(struct btrfs_root *root,
+				struct btrfs_path *path,
+				u64 objectid,
+				void (*iterator)(void *,
+						 const struct prop_handler *,
+						 const char *,
+						 size_t),
+				void *ctx)
+{
+	int ret;
+	char *name_buf = NULL;
+	char *value_buf = NULL;
+	int name_buf_len = 0;
+	int value_buf_len = 0;
+
+	while (1) {
+		struct btrfs_key key;
+		struct btrfs_dir_item *di;
+		struct extent_buffer *leaf;
+		u32 total_len, cur, this_len;
+		int slot;
+		const struct hlist_head *handlers;
+
+		slot = path->slots[0];
+		leaf = path->nodes[0];
+
+		if (slot >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret < 0)
+				goto out;
+			else if (ret > 0)
+				break;
+			continue;
+		}
+
+		btrfs_item_key_to_cpu(leaf, &key, slot);
+		if (key.objectid != objectid)
+			break;
+		if (key.type != BTRFS_XATTR_ITEM_KEY)
+			break;
+
+		handlers = find_prop_handlers_by_hash(key.offset);
+		if (!handlers)
+			goto next_slot;
+
+		di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
+		cur = 0;
+		total_len = btrfs_item_size_nr(leaf, slot);
+
+		while (cur < total_len) {
+			u32 name_len = btrfs_dir_name_len(leaf, di);
+			u32 data_len = btrfs_dir_data_len(leaf, di);
+			unsigned long name_ptr, data_ptr;
+			const struct prop_handler *handler;
+
+			this_len = sizeof(*di) + name_len + data_len;
+			name_ptr = (unsigned long)(di + 1);
+			data_ptr = name_ptr + name_len;
+
+			if (name_len <= XATTR_BTRFS_PREFIX_LEN ||
+			    memcmp_extent_buffer(leaf, XATTR_BTRFS_PREFIX,
+						 name_ptr,
+						 XATTR_BTRFS_PREFIX_LEN))
+				goto next_dir_item;
+
+			if (name_len >= name_buf_len) {
+				kfree(name_buf);
+				name_buf_len = name_len + 1;
+				name_buf = kmalloc(name_buf_len, GFP_NOFS);
+				if (!name_buf) {
+					ret = -ENOMEM;
+					goto out;
+				}
+			}
+			read_extent_buffer(leaf, name_buf, name_ptr, name_len);
+			name_buf[name_len] = '\0';
+
+			handler = find_prop_handler(name_buf, handlers);
+			if (!handler)
+				goto next_dir_item;
+
+			if (data_len > value_buf_len) {
+				kfree(value_buf);
+				value_buf_len = data_len;
+				value_buf = kmalloc(data_len, GFP_NOFS);
+				if (!value_buf) {
+					ret = -ENOMEM;
+					goto out;
+				}
+			}
+			read_extent_buffer(leaf, value_buf, data_ptr, data_len);
+
+			iterator(ctx, handler, value_buf, data_len);
+next_dir_item:
+			cur += this_len;
+			di = (struct btrfs_dir_item *)((char *) di + this_len);
+		}
+
+next_slot:
+		path->slots[0]++;
+	}
+
+	ret = 0;
+out:
+	btrfs_release_path(path);
+	kfree(name_buf);
+	kfree(value_buf);
+
+	return ret;
+}
+
+static void inode_prop_iterator(void *ctx,
+				const struct prop_handler *handler,
+				const char *value,
+				size_t len)
+{
+	struct inode *inode = ctx;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	int ret;
+
+	ret = handler->apply(inode, value, len);
+	if (unlikely(ret))
+		btrfs_warn(root->fs_info,
+			   "error applying prop %s to ino %llu (root %llu): %d",
+			   handler->xattr_name, btrfs_ino(inode),
+			   root->root_key.objectid, ret);
+	else
+		set_bit(BTRFS_INODE_HAS_PROPS, &BTRFS_I(inode)->runtime_flags);
+}
+
+int btrfs_load_inode_props(struct inode *inode, struct btrfs_path *path)
+{
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	u64 ino = btrfs_ino(inode);
+	int ret;
+
+	ret = iterate_object_props(root, path, ino, inode_prop_iterator, inode);
+
+	return ret;
+}
+
+static int inherit_props(struct btrfs_trans_handle *trans,
+			 struct inode *inode,
+			 struct inode *parent)
+{
+	const struct prop_handler *h;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	int ret;
+
+	if (!test_bit(BTRFS_INODE_HAS_PROPS,
+		      &BTRFS_I(parent)->runtime_flags))
+		return 0;
+
+	for (h = &prop_handlers[0]; h->xattr_name; h++) {
+		const char *value;
+		u64 num_bytes;
+
+		if (!h->inheritable)
+			continue;
+
+		value = h->extract(parent);
+		if (!value)
+			continue;
+
+		num_bytes = btrfs_calc_trans_metadata_size(root, 1);
+		ret = btrfs_block_rsv_add(root, trans->block_rsv,
+					  num_bytes, BTRFS_RESERVE_NO_FLUSH);
+		if (ret)
+			goto out;
+		ret = __btrfs_set_prop(trans, inode, h->xattr_name,
+				       value, strlen(value), 0);
+		btrfs_block_rsv_release(root, trans->block_rsv, num_bytes);
+		if (ret)
+			goto out;
+	}
+	ret = 0;
+out:
+	return ret;
+}
+
+int btrfs_inode_inherit_props(struct btrfs_trans_handle *trans,
+			      struct inode *inode,
+			      struct inode *dir)
+{
+	if (!dir)
+		return 0;
+
+	return inherit_props(trans, inode, dir);
+}
+
+int btrfs_subvol_inherit_props(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *root,
+			       struct btrfs_root *parent_root)
+{
+	struct btrfs_key key;
+	struct inode *parent_inode, *child_inode;
+	int ret;
+
+	key.objectid = BTRFS_FIRST_FREE_OBJECTID;
+	key.type = BTRFS_INODE_ITEM_KEY;
+	key.offset = 0;
+
+	parent_inode = btrfs_iget(parent_root->fs_info->sb, &key,
+				  parent_root, NULL);
+	if (IS_ERR(parent_inode))
+		return PTR_ERR(parent_inode);
+
+	child_inode = btrfs_iget(root->fs_info->sb, &key, root, NULL);
+	if (IS_ERR(child_inode)) {
+		iput(parent_inode);
+		return PTR_ERR(child_inode);
+	}
+
+	ret = inherit_props(trans, child_inode, parent_inode);
+	iput(child_inode);
+	iput(parent_inode);
+
+	return ret;
+}
+
+static int prop_compression_validate(const char *value, size_t len)
+{
+	if (!strncmp("lzo", value, len))
+		return 0;
+	else if (!strncmp("zlib", value, len))
+		return 0;
+
+	return -EINVAL;
+}
+
+static int prop_compression_apply(struct inode *inode,
+				  const char *value,
+				  size_t len)
+{
+	int type;
+
+	if (len == 0) {
+		BTRFS_I(inode)->flags |= BTRFS_INODE_NOCOMPRESS;
+		BTRFS_I(inode)->flags &= ~BTRFS_INODE_COMPRESS;
+		BTRFS_I(inode)->force_compress = BTRFS_COMPRESS_NONE;
+
+		return 0;
+	}
+
+	if (!strncmp("lzo", value, len))
+		type = BTRFS_COMPRESS_LZO;
+	else if (!strncmp("zlib", value, len))
+		type = BTRFS_COMPRESS_ZLIB;
+	else
+		return -EINVAL;
+
+	BTRFS_I(inode)->flags &= ~BTRFS_INODE_NOCOMPRESS;
+	BTRFS_I(inode)->flags |= BTRFS_INODE_COMPRESS;
+	BTRFS_I(inode)->force_compress = type;
+
+	return 0;
+}
+
+static const char *prop_compression_extract(struct inode *inode)
+{
+	switch (BTRFS_I(inode)->force_compress) {
+	case BTRFS_COMPRESS_ZLIB:
+		return "zlib";
+	case BTRFS_COMPRESS_LZO:
+		return "lzo";
+	}
+
+	return NULL;
+}

fs/btrfs/props.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2014 Filipe David Borba Manana <fdmanana@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#ifndef __BTRFS_PROPS_H
+#define __BTRFS_PROPS_H
+
+#include "ctree.h"
+
+void __init btrfs_props_init(void);
+
+int btrfs_set_prop(struct inode *inode,
+		   const char *name,
+		   const char *value,
+		   size_t value_len,
+		   int flags);
+
+int btrfs_load_inode_props(struct inode *inode, struct btrfs_path *path);
+
+int btrfs_inode_inherit_props(struct btrfs_trans_handle *trans,
+			      struct inode *inode,
+			      struct inode *dir);
+
+int btrfs_subvol_inherit_props(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *root,
+			       struct btrfs_root *parent_root);
+
+#endif

fs/btrfs/super.c

@@ -48,6 +48,7 @@
 #include "transaction.h"
 #include "btrfs_inode.h"
 #include "print-tree.h"
+#include "props.h"
 #include "xattr.h"
 #include "volumes.h"
 #include "export.h"
@@ -1865,6 +1866,8 @@ static int __init init_btrfs_fs(void)
 {
 	int err;
 
+	btrfs_props_init();
+
 	err = btrfs_init_sysfs();
 	if (err)
 		return err;

fs/btrfs/xattr.c

@@ -27,6 +27,7 @@
 #include "transaction.h"
 #include "xattr.h"
 #include "disk-io.h"
+#include "props.h"
 
 
 ssize_t __btrfs_getxattr(struct inode *inode, const char *name,
@@ -331,7 +332,8 @@ static bool btrfs_is_valid_xattr(const char *name)
 			XATTR_SECURITY_PREFIX_LEN) ||
 	       !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) ||
 	       !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
-	       !strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN);
+	       !strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) ||
+		!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN);
 }
 
 ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
@@ -373,6 +375,10 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 	if (!btrfs_is_valid_xattr(name))
 		return -EOPNOTSUPP;
 
+	if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
+		return btrfs_set_prop(dentry->d_inode, name,
+				      value, size, flags);
+
 	if (size == 0)
 		value = "";  /* empty EA, do not remove */
 
@@ -402,6 +408,10 @@ int btrfs_removexattr(struct dentry *dentry, const char *name)
 	if (!btrfs_is_valid_xattr(name))
 		return -EOPNOTSUPP;
 
+	if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
+		return btrfs_set_prop(dentry->d_inode, name,
+				      NULL, 0, XATTR_REPLACE);
+
 	return __btrfs_setxattr(NULL, dentry->d_inode, name, NULL, 0,
 				XATTR_REPLACE);
 }

include/uapi/linux/xattr.h

@@ -20,6 +20,9 @@
 #define XATTR_MAC_OSX_PREFIX "osx."
 #define XATTR_MAC_OSX_PREFIX_LEN (sizeof(XATTR_MAC_OSX_PREFIX) - 1)
 
+#define XATTR_BTRFS_PREFIX "btrfs."
+#define XATTR_BTRFS_PREFIX_LEN (sizeof(XATTR_BTRFS_PREFIX) - 1)
+
 #define XATTR_SECURITY_PREFIX	"security."
 #define XATTR_SECURITY_PREFIX_LEN (sizeof(XATTR_SECURITY_PREFIX) - 1)