On 10.06.2017 17:37, Hy Che wrote: > Hello everyone, > My name is Hy (ugen on freenode), I am a student attending GSoC for > Haiku[1]. Because I have a project that support write features for > BtrFS[2], there are some questions, since the documents on wiki are > not enough so I have to ask here. > > 1. Where can I find to read a complete btree manipulations in detail > (split, insert, etc) for BtrFS except the code base ? I need to get > the idea first.
Have you read this paper: https://dl.acm.org/authorize?N80838 The original idea came by Ohad Rodeh while he was at IBM. I believe this was the initial paper: https://dl.acm.org/authorize?N80839 > > 2. About the reference, " ...with a refcount associated to each tree > node but stored in an ad-hoc free map structure ... " - wikipedia. > What is a free map structure, and where does it stored ? I believe you are looking for this : https://btrfs.wiki.kernel.org/index.php/Btrfs_design#Reference_Counted_Extents http://www.spinics.net/lists/linux-btrfs/msg33415.html > > 3. How BtrFS allocate block and extent when cow-ed ? As I tested after > making a new file, the root tree root, extent root and csum root move > forward 65536 bytes, the fs root move 49152 bytes and the data extent > is allocated next to the previous one. Where those numbers come from ? > Is data extent is cow-ed ? I see it doesn't because extent-item still > contains the old offset. You'd have to read the code, have you taken a look at : __btrfs_cow_block() > > 4. How BtrFS handle transactions ? > Correctly me if I'm wrong, the transaction collect all requests in 30 > seconds and then write back to disk. The transid increments when new > request appeared and genid is asigned to this one. I don't think there is anything written per-se. You'd again have to resort to reading the code > > 5. Why there is unused space (100 bytes) at the end of each node ? > 6. How does BtrFS calculate checksum ? It uses a 32bit CRC. The actual function which is used to calc the csum is csum_tree_block you can check its callers and internals to in which code paths the crc is used. But in general all it does is call btrfs_csum_data on the extent buffer which holds the particular block. > > > [1]: About Haiku: www.haiku-os.org > [2]: My project info on GSoC: > https://summerofcode.withgoogle.com/projects/4749427110576128 > > Thanks, > Hy > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
