Re: [ANNOUNCE] bcachefs!

[Ming Lin <mlin@kernel.org>]

On Tue, 2015-07-28 at 11:45 -0700, Ming Lin wrote:
> On Tue, Jul 28, 2015 at 11:41 AM, Ming Lin <mlin@kernel.org> wrote:
> > On Fri, Jul 24, 2015 at 1:47 PM, Ming Lin <mlin@kernel.org> wrote:
> >>
> >> And I want to learn how the btree node insert/delete/update happens on
> >> disk. These maybe too detail. I'm going to write a small tool to dump
> >> the file system. Then I could understand better the on disk btree
> >> format.
> >
> > Here is my simple tool to dump parts of the on-disk format.
> > http://www.minggr.net/cgit/cgit.cgi/bcache-tools/commit/?id=deb258e2
> 
> Actually: http://www.minggr.net/cgit/cgit.cgi/bcache-tools/commit/?id=3121eec
> 
> >
> > It's not in good shape, but simple enough to learn the on-disk format.

Hi Kent,

I'm trying to understand how the root inode is stored in the inode
btree.

dd if=/dev/zero of=fs.img bs=10M count=1
bcacheadm format -C fs.img
mount -t bcache -o loop fs.img /mnt
umount /mnt
hexdump -C fs.img > fs.hex

From my simple tool, I know that the inode btree starts from offset
0xec000

000ec000  43 ef f3 df ff ff ff ff  86 c1 47 1e 99 25 51 35  |C.........G..%Q5|
000ec010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000ec020  00 00 00 00 00 00 00 00  ff ff ff ff ff ff ff ff  |................|
000ec030  ff ff ff ff ff ff ff ff  01 05 00 00 00 00 00 00  |................|
000ec040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000ec070  88 b5 38 e2 45 36 eb f6  00 00 00 00 00 00 00 00  |..8.E6..........|
000ec080  01 00 00 00 03 00 00 00  00 00 00 00 00 00 00 00  |................|
000ec090  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000ed000  31 66 fd 31 ff ff ff ff  88 b5 38 e2 45 36 eb f6  |1f.1......8.E6..|
000ed010  02 00 00 00 00 00 00 00  01 00 00 00 03 00 0b 00  |................|
000ed020  0b 01 80 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000ed030  00 00 00 00 00 00 00 00  00 10 00 00 00 00 00 00  |................|
000ed040  ed 41 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.A..............|
000ed050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000ed070  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000ed080  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*

btree_node (0xec000)
    bset (0xed008)  ---> bset->u64s = 0x0b = 11
        bkey_packed (0xed020)
            bkey (0xed020)
            bch_inode (0xed040 to 0xed077)  ---> root inode

Is the decode above correct?

I found the root inode manually. But how is it actually found by code?

Could you help to explain what it is from 0xec070 to 0xed007?
Are they also bsets?

Thanks,
Ming