Btrfs devel - Jan 2008 - [ANNOUNCE] Btrfs v0.10 (online growing/shrinking, ext3 conversion, and more)

Hello everyone,

Btrfs v0.10 is now available for download from:

http://oss.oracle.com/projects/btrfs/

Btrfs is still in an early alpha state, and the disk format is not finalized.
v0.10 introduces a new disk format, and is not compatible with v0.9.

The core of this release is explicit back references for all metadata blocks,
data extents, and directory items.  These are a crucial building block for
future features such as online fsck and migration between devices.  The back
references are verified during deletes, and the extent back references are
checked by the existing offline fsck tool.

For all of the details of how the back references are maintained, please
see the design document:

http://oss.oracle.com/projects/btrfs/dist/documentation/btrfs-design.html

Other new features (described in detail below):

* Online resizing (including shrinking)
* In place conversion from Ext3 to Btrfs
* data=ordered support
* Mount options to disable data COW and checksumming 
* Barrier support for sata and IDE drives

[ Resizing ]

In order to demonstrate and test the back references, I've added an online
resizer, which can both grow and shrink the filesystem:

mount -t btrfs /dev/xxx /mnt

# add 2GB to the FS
btrfsctl -r +2g /mnt

# shrink the FS by 4GB
btrfsctl -r -4g /mnt

# Explicitly set the FS size
btrfsctl -r 20g /mnt

# Use 'max' to grow the FS to the limit of the device
btrfsctl -r max /mnt

[ Conversion from Ext3 ]

This is an offline, in place, conversion program written by Yan Zheng.  It
has been through basic testing, but should not be trusted with critical data.

To build the conversion program, run 'make convert' in the btrfs-progs
tree. It depends on libe2fs and acl development libraries.

The conversion program uses the copy on write nature of Btrfs to preserve the
original Ext3 FS, sharing the data blocks between Btrfs and Ext3 metadata.
Btrfs metadata is created inside the free space of the Ext3 filesystem, and it
is possible to either make the conversion permanent (reclaiming the space used
by Ext3) or roll back the conversion to the original Ext3 filesystem.

More details and example usage of the conversion program can be found here:

http://oss.oracle.com/projects/btrfs/dist/documentation/btrfs-converter.html

Thanks to Yan Zheng for all of his work on the converter.

[ New mount options ]

mount -o nodatacsum disables checksumming on data extents

mount -o nodatacow disables copy on write of data extents, unless a given
extent is referenced by more than one snapshot.  This is targeted at database
workloads, where copy on write is not optimal for performance.

The explicit back references allow the nodatacow code to make sure copy
on write is done when multiple snapshots reference the same file, maintaining
snapshot consistency.

mount -o alloc_start=num forces allocation hints to start at least num bytes
into the disk.  This was introduced to test the resizer.  Example usage:

mount -o alloc_start=16g /dev/xxxx /mnt
(do something to the FS)
btrfsctl -r 12g /mnt

The btrfsctl command will resize the FS down to 12GB in size.  Because
the FS was mounted with -o alloc_start=16g, any allocations done after
mounting will need to be relocated by the resizer.

It is safe to specify a number past the end of the FS, if the alloc_start is too
large, it is ignored.

mount -o nobarrier disables cache flushes during commit.

-chris

On Tue, Jan 15, 2008 at 10:52:38AM -0500, Chris Mason
wrote:
> http://oss.oracle.com/projects/btrfs/
> 
> Btrfs is still in an early alpha state, and the disk format is not
finalized.
> v0.10 introduces a new disk format, and is not compatible with v0.9.
> 
Looks like fun. btrfsck fails to check if it actually received a
dev argument though, so if you don''t pass a device, we get a nice
segfault.

Signed-off-by: Kyle McMartin <kmcmartin@redhat.com>

---
diff -Nur btrfs-progs-0.10/btrfsck.c btrfs-progs-0.10-kyle/btrfsck.c
--- btrfs-progs-0.10/btrfsck.c	2008-01-15 10:33:32.000000000 -0500
+++ btrfs-progs-0.10-kyle/btrfsck.c	2008-01-15 11:49:24.000000000 -0500
@@ -709,6 +709,11 @@
 	return err;
 }
 
+void print_usage(void) {
+	fprintf(stderr, "usage: btrfsck dev\n");
+	exit(1);
+}
+
 int main(int ac, char **av) {
 	struct btrfs_root *root;
 	struct cache_tree extent_cache;
@@ -727,6 +732,9 @@
 	int slot;
 	struct btrfs_root_item ri;
 
+	if (ac < 2)
+		print_usage();
+
 	radix_tree_init();
 	cache_tree_init(&extent_cache);
 	cache_tree_init(&seen);
-
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CM> mount -o nodatacow disables copy on write of data extents
And how btrfs behaves with disabled COW in terms of reliability? Much like
ext2fs?

CM> mount -o nobarrier disables cache flushes during commit.
What is and what for "write barrier"?

Thanks.

On Tuesday 15 January 2008, Chris Mason wrote:
> Hello everyone,
>
> Btrfs v0.10 is now available for download from:
It does not even compile for me, tested with 2.6.24-rc{7,8}. I will look at 
that later.

fs/built-in.o: In function `btrfs_xattr_set_acl'':
acl.c:(.text+0x68f33): undefined reference to `posix_acl_from_xattr''
acl.c:(.text+0x68f47): undefined reference to `posix_acl_valid''
make: *** [.tmp_vmlinux1] Error 1

Is this release supposed to fix the suspend problem?
-- 
Regards,
Chris
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On Tuesday 15 January 2008, Chris Mason wrote:
> Hello everyone,
>
> Btrfs v0.10 is now available for download from:
>
> http://oss.oracle.com/projects/btrfs/
Well, it turns out this release had a few small problems:

* data=ordered deadlock on older kernels (including 2.6.23)
* Compile problems when ACLs were not enabled in the kernel

So, I've put v0.11 out there.  It fixes those two problems and will also 
compile on older (2.6.18) enterprise kernels.

v0.11 does not have any disk format changes.

-chris

On Thursday 17 January 2008, Chris mason wrote:
> So, I''ve put v0.11 out there.
Ok, back to the suspend problem I mentioned:

Jan 18 00:04:40 revo WARNING: at fs/btrfs/tree-defrag.c:74 defrag_walk_down()
Jan 18 00:04:40 revo Pid: 258, comm: btrfs/0 Not tainted 2.6.24-rc8 #1
Jan 18 00:04:40 revo [<b01ddef3>] btrfs_defrag_leaves+0x273/0x8c0
Jan 18 00:04:40 revo [<b01d5b57>] btrfs_defrag_root+0x67/0xe0
Jan 18 00:04:40 revo [<b01d5c43>] btrfs_defrag_dirty_roots+0x73/0x80
Jan 18 00:04:40 revo [<b01d5c50>] btrfs_transaction_cleaner+0x0/0xd0
Jan 18 00:04:40 revo [<b01d5cf2>] btrfs_transaction_cleaner+0xa2/0xd0
Jan 18 00:04:40 revo [<b013911d>] run_workqueue+0xad/0x130
Jan 18 00:04:40 revo [<b0139b80>] worker_thread+0x0/0xf0
Jan 18 00:04:40 revo [<b0139c0c>] worker_thread+0x8c/0xf0
Jan 18 00:04:40 revo [<b013d100>] autoremove_wake_function+0x0/0x40
Jan 18 00:04:40 revo [<b0139b80>] worker_thread+0x0/0xf0
Jan 18 00:04:40 revo [<b013ce42>] kthread+0x42/0x70
Jan 18 00:04:40 revo [<b013ce00>] kthread+0x0/0x70
Jan 18 00:04:40 revo [<b0104ea7>] kernel_thread_helper+0x7/0x10
Jan 18 00:04:40 revo ======================Jan 18 00:04:40 revo BUG: unable to
handle kernel NULL pointer dereference at
virtual address 0000001c
Jan 18 00:04:40 revo printing eip: b01d3c58 *pde = 00000000
Jan 18 00:04:40 revo Oops: 0000 [#1] SMP
Jan 18 00:04:40 revo Modules linked in: iwl3945
Jan 18 00:04:40 revo
Jan 18 00:04:40 revo Pid: 258, comm: btrfs/0 Not tainted (2.6.24-rc8 #1)
Jan 18 00:04:40 revo EIP: 0060:[<b01d3c58>] EFLAGS: 00010292 CPU: 0
Jan 18 00:04:40 revo EIP is at btrfs_clear_buffer_defrag+0x18/0x80
Jan 18 00:04:40 revo EAX: 00000000 EBX: 00000000 ECX: eec6d528 EDX: eec6d528
Jan 18 00:04:40 revo ESI: ee544200 EDI: ee40c000 EBP: 00000040 ESP: ee40de8c
Jan 18 00:04:40 revo DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
Jan 18 00:04:40 revo Process btrfs/0 (pid: 258, ti=ee40c000 task=ef0ab570 
task.ti=ee40c000)
Jan 18 00:04:40 revo Stack: 00100fff 00000000 00000040 00000000 d343bdbc 
eec37634 ee544200 00000000
Jan 18 00:04:40 revo ee544200 ee40c000 00000000 b01de0b5 eec37e14 00000000 
ee40df14 b04b6a09
Jan 18 00:04:40 revo 00000001 eedf23e4 eec6d528 00000000 02ba5cc0 eec37e14 
01000000 00000010
Jan 18 00:04:40 revo Call Trace:
Jan 18 00:04:40 revo [<b01de0b5>] btrfs_defrag_leaves+0x435/0x8c0
Jan 18 00:04:40 revo [<b01d5b57>] btrfs_defrag_root+0x67/0xe0
Jan 18 00:04:40 revo [<b01d5c43>] btrfs_defrag_dirty_roots+0x73/0x80
Jan 18 00:04:40 revo [<b01d5c50>] btrfs_transaction_cleaner+0x0/0xd0
Jan 18 00:04:40 revo [<b01d5cf2>] btrfs_transaction_cleaner+0xa2/0xd0
Jan 18 00:04:40 revo [<b013911d>] run_workqueue+0xad/0x130
Jan 18 00:04:40 revo [<b0139b80>] worker_thread+0x0/0xf0
Jan 18 00:04:40 revo [<b0139c0c>] worker_thread+0x8c/0xf0
Jan 18 00:04:40 revo [<b013d100>] autoremove_wake_function+0x0/0x40
Jan 18 00:04:40 revo [<b0139b80>] worker_thread+0x0/0xf0
Jan 18 00:04:40 revo [<b013ce42>] kthread+0x42/0x70
Jan 18 00:04:40 revo [<b013ce00>] kthread+0x0/0x70
Jan 18 00:04:40 revo [<b0104ea7>] kernel_thread_helper+0x7/0x10
Jan 18 00:04:40 revo ======================Jan 18 00:04:40 revo Code: 24 1c 8b
74 24 20 8b 7c 24 24 8b 6c 24 28 83 c4 2c
c3 90 83 ec 2c 89 74 24 20 89 6c 24 28 bd 40 00 00 00 89 5c 24 1c 89 7c 24 24 
<8b> 58 1c 8b 10 8b 48 04 8b 5b 10 89 ce 8b 1b 8b 5b b8 8b 9b bc
Jan 18 00:04:40 revo EIP: [<b01d3c58>] btrfs_clear_buffer_defrag+0x18/0x80
SS:ESP 0068:ee40de8c
Jan 18 00:04:40 revo ---[ end trace f7750d79e5545648 ]---

I get this after a suspend/resume cycle with mounted btrfs.
-- 
Regards,
Chris
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