On 2020/6/18 下午10:53, Rebraca Dejan (BSOT/PJ-ES1-Bg) wrote: > Hi Qu, > > I've read this: > https://btrfs.wiki.kernel.org/index.php/Data_Structures#btrfs_key_.2F_btrfs_disk_key > where key.objectid of EXTENT_ITEM contains the starting byte offset of the extent it describes and key.offset of EXTENT_ITEM stores the size of the extent the item describes. > > From your dump: > item 6 key (257 EXTENT_DATA 0) itemoff 13794 itemsize 2069 > > itremoff = 13794 > This is the offset relative to tree block or tree leaf, right? Right, but you still need to consider the offset inside btrfs_file_extent_item for inline data, that's why I'm using btrfs_file_extent_inline_start() to find out the real offset. Thanks, Qu > > Thanks, > Dejan > > > -----Original Message----- > From: Qu Wenruo <quwenruo.btrfs@xxxxxxx> > Sent: četvrtak, 18. jun 2020. 15:46 > To: Rebraca Dejan (BSOT/PJ-ES1-Bg) <Dejan.Rebraca@xxxxxxxxxxxx>; linux-btrfs@xxxxxxxxxxxxxxx > Subject: Re: Physical address offset of the inline extent > > > > On 2020/6/18 下午9:21, Rebraca Dejan (BSOT/PJ-ES1-Bg) wrote: >> Hi, >> >> Does anybody know how to get an address offset of the file data inline extent? > > Since it's inline, it's inlined into metadata (tree block), thus makes no sense to get the "address". > > The address will be inside a tree block anyway. > > If you really want the address, you can check it with dump-tree. > > $ btrfs ins dump-tree -t 5 /dev/nvme/btrfs fs tree key (FS_TREE ROOT_ITEM 0) leaf 5324800 items 7 free space 13619 generation 6 owner FS_TREE leaf 5324800 flags 0x1(WRITTEN) backref revision 1 > ^^^^^^^ Tree block bytenr > ... > item 6 key (257 EXTENT_DATA 0) itemoff 13794 itemsize 2069 > generation 6 type 0 (inline) > inline extent data size 2048 ram_bytes 2048 compression > 0 (none) > > You need to use extent_buffer to grab the inline file extent item, and use the btrfs_file_extent_inline_start() to get the inline file extent offset inside the leaf. > > Anyway, you need a solid understanding of btrfs on-disk format to grasp the above dump. > >> Kernel returns 0 trough FS_IOC_FIEMAP ioctl, but I would really like to get real physical offset if possible, most probably meaning: >> >> In FS tree - on-disk address of the extent data item for the relevant file object + the offset within that item (0x15). >> >> I was hoping that the key.objectid of key.type = EXTENT_ITEM would give me such an information, but apparently this is not the case. > > Key.objectid of EXTENT_ITEM only means the inode number. > Key.offset of EXTENT_ITEM means the file offset, for inline file extent it's always 0. > > So it looks like you're not familiar with btrfs on-disk format, thus I doubt the usefulness of known the inline file extent offset inside the tree block. > > Thanks, > Qu > >> >> Thanks very much, >> >> Dejan >> >> >> >
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