From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH v5 0/3] btrfs: more explaination on extent_map members
Date: Tue, 16 Apr 2024 09:05:37 +0930 [thread overview]
Message-ID: <cover.1713224013.git.wqu@suse.com> (raw)
[REPO]
https://github.com/adam900710/linux.git/ em_cleanup
The first 3 patches only. As later patches are the huge rename part.
[CHANGELOG]
v5:
- Update the comment on extent map merging part
v4:
- Add extra comments for the extent map merging
Since extent maps can be merged, the members are only matching
on-disk file extent items before merging.
This also means users of extent_map should not rely on it for
a reliable file extent item member.
(That's also why we use ordered_extent not extent_maps, to update
file extent items)
v3:
- Rebased to latest for-next branch
- Further comments polishment
- Coding style update to follow the guideline
v2:
- Add Filipe's cleanup on mod_start/mod_len
These two members are no longer utilized, saving me quite some time on
digging into their usage.
- Update the comments of the extent_map structure
To make them more readable and less confusing.
- Further cleanup for inline extent_map reading
- A new patch to do extra sanity checks for create_io_em()
Firstly pure NOCOW writes should not call create_io_em(), secondly
with the new knowledge of extent_map, it's easier to do extra sanity
checks for the already pretty long parameter list.
Btrfs uses extent_map to represent a in-memory file extent.
There are severam members that are 1:1 mappe in on-disk file extent
items and extent maps:
- extent_map::start == key.offset
- extent_map::len == file_extent_num_bytes
- extent_map::ram_bytes == file_extent_ram_bytes
But that's all, the remaining are pretty different:
- Use block_start to indicate holes/inline extents
Meanwhile btrfs on-disk file extent items go with a dedicated type for
inline extents, and disk_bytenr 0 for holes.
- Weird block_start/orig_block_len/orig_start
In theory we can directly go with the same file_extent_disk_bytenr,
file_extent_disk_num_bytes and file_extent_offset to calculate the
remaining members (block_start/orig_start/orig_block_len/block_len).
But for whatever reason, we didn't go that path and have a hell of
weird and inconsistent calculation for them.
Qu Wenruo (3):
btrfs: add extra comments on extent_map members
btrfs: simplify the inline extent map creation
btrfs: add extra sanity checks for create_io_em()
fs/btrfs/extent_map.h | 56 ++++++++++++++++++++++++++++++++++++++++++-
fs/btrfs/file-item.c | 20 ++++++++--------
fs/btrfs/inode.c | 40 ++++++++++++++++++++++++++++++-
3 files changed, 104 insertions(+), 12 deletions(-)
--
2.44.0
next reply other threads:[~2024-04-15 23:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 23:35 Qu Wenruo [this message]
2024-04-15 23:35 ` [PATCH v5 1/3] btrfs: add extra comments on extent_map members Qu Wenruo
2024-04-15 23:35 ` [PATCH v5 2/3] btrfs: simplify the inline extent map creation Qu Wenruo
2024-04-15 23:35 ` [PATCH v5 3/3] btrfs: add extra sanity checks for create_io_em() Qu Wenruo
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