2.8.0

SingleBuffer v2 layout

Important

By default, the v2 layout will only apply to new file systems.
Existing v1 layout file systems will not be upgraded automatically.
You can pass v2: true to the backend to upgrade existing v1 layouts.
Passing v2: false (must be literally false) will force the v1 layout.

This release introduces a new disk layout for SingleBuffer, which uses a CoW B+ tree. This has resulted in faster random reads and writes:

Benchmark	File	Ops	v1 avg/op	v1 MB/s	v2 avg/op	v2 MB/s	Speedup
Read	1 MiB	256	163 µs	25.2	35 µs	116.9	4.6×
Read	8 MiB	1024	1,019 µs	4.0	20 µs	206.9	51×
Read	32 MiB	1024	10,780 µs	0.38	18 µs	230.8	607×
Write, cached + close	1 MiB	256	13 µs	311.2	17 µs	247.2	~1×
Write, cached + close	8 MiB	1024	1,461 µs	2.8	325 µs	12.6	4.5×
Write, O_SYNC	1 MiB	256	600 µs	6.8	240 µs	17.1	2.5×
Write, O_SYNC	8 MiB	1024	3,471 µs	1.18	666 µs	6.15	5.2×

Before, allocations would never be freed in order to keep the allocator as simple as possible. The new layout replaces this behavior, which results in much better space utilization:

Benchmark	Buffer	v1 result	v2 result
Write then delete one 4 KiB file ×10,000 (#323)	1 MiB	Failed after 126 ops, 1.05 MB	26 KB
Random 4 KiB O_SYNC writes ×2048, 8 MiB file	32 MiB	8.40 MB	8.42 MB
Append 4 KiB ×1024 (to 4 MiB)	32 MiB	Failed after 127 ops, 33.8 MB	5.41 MB
2000 files of 1 KiB, one directory	32 MiB	31.6 MB	10.5 MB
Mixed creates, overwrites, deletes (0-64 KiB) ×5000	16 MiB	Failed after 707 ops, 16.8 MB	5.29 MB

Supporting changes:

• StoreFS.allocNew now supports allocations done by the store
• Fixed partial stores not being able to differentiate replacements
• Added sbfs v1->v2 upgrade path
• Added version checking to SingleBuffer
• Added sbfs r/w benchmarks

umask

This release also adds support for umask. This applies to contexts and masks bits on created files' permissions mods. See man umask(2) for more information. This was initially drafted in #326.

Misc. / Bug Fixes

• Fixed metadata operations failing on directories and needing permissions (#327)
• Fixed VFS async open checking creation mode instead of existing file mode
• Fixed Async() not having async operations wait for the queue