COM0 and LPT0 are not listed in the official Microsoft's documentation
at https://docs.microsoft.com/windows/win32/fileio/naming-a-file, but
in reality are also invalid in Windows Explorer.
Signed-off-by: Tomasz Wilczyński <twilczynski@naver.com>
Add specific errors for the failures, resulting in this rather than just
the generic "invalid filename":
[MRIW7] 08:50:50 INFO: Puller (folder default, item "NUL"): syncing: filename is invalid: name is reserved
[MRIW7] 08:50:50 INFO: Puller (folder default, item "fail."): syncing: filename is invalid: name ends with space or period
[MRIW7] 08:50:50 INFO: Puller (folder default, item "sup:yo"): syncing: filename is invalid: name contains reserved character
[MRIW7] 08:50:50 INFO: default: Failed to sync 3 items
Use the IoctlFileClone and IoctlFileCloneRange ioctl wrappers and the
FileCloneRange type provided by golang.org/x/sys/unix instead of
locally implementing them. This also allows to re-enable the code for
ppc/ppc64/ppc64le again (see commit 758a1a6a37 ("lib/fs: Disable ioctl
on ppc (fixes#6898) (#6901)")) since golang.org/x/sys/unix internally
uses the correct FICLONE and FICLONERANGE values depending on $GOARCH.
Most notably, it now detects all-lowercase files and returns these
as-is. The tests have been expanded with two cases and are now used
as a benchmark (admittedly a rather trivial one).
name old time/op new time/op delta
UnicodeLowercaseMaybeChange-8 4.59µs ± 2% 4.57µs ± 1% ~ (p=0.197 n=10+10)
UnicodeLowercaseNoChange-8 3.26µs ± 1% 3.09µs ± 1% -5.27% (p=0.000 n=9+10)
This changes the cache to cache less things, yet retain the required
efficiency for our walk usecase. This uses less memory.
Specifically, instead of keeping result and child caches for each path
level, only keep a single cached child. In practice our operations are
depth-first, or almost depth-first, and then we retain the same hit
ratio for a smaller cache size.
I improved the benchmark so that it counts the Lstat and DirNames
operations performed, and they do not change significantly. The amount
of allocated memory is reduced by 20% and the walk itself is actually
slightly faster.
This also removes the clear based on number of cached names (as that is
not a thing any more) and the timer based clear (which was unused). This
means we'll retain the last cache state forever until it's cleared by a
write operation, but we did that before too and that state is now a lot
smaller...
The overhead compared to not using a casefs, for our typical "double
walk" (walk the tree then stat everything again) is 2x the dirnames we
would otherwise call, and no overhead on the stats (unchanged from old
implementation)
```
name old time/op new time/op delta
WalkCaseFakeFS100k/rawfs-8 306ms ± 1% 305ms ± 2% ~ (p=0.182 n=9+10)
WalkCaseFakeFS100k/casefs-8 579ms ± 5% 557ms ± 1% -3.77% (p=0.000 n=10+10)
name old B/entry new B/entry delta
WalkCaseFakeFS100k/rawfs-8 590 ± 0% 590 ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 1.09k ± 0% 0.87k ± 0% -19.98% (p=0.000 n=10+10)
name old DirNames/entry new DirNames/entry delta
WalkCaseFakeFS100k/rawfs-8 0.51 ± 0% 0.51 ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 1.02 ± 0% 1.02 ± 0% ~ (all equal)
name old DirNames/op new DirNames/op delta
WalkCaseFakeFS100k/rawfs-8 51.2k ± 0% 51.2k ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 102k ± 0% 102k ± 0% ~ (all equal)
name old Lstat/entry new Lstat/entry delta
WalkCaseFakeFS100k/rawfs-8 3.02 ± 0% 3.02 ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 3.02 ± 0% 3.02 ± 0% ~ (all equal)
name old Lstat/op new Lstat/op delta
WalkCaseFakeFS100k/rawfs-8 302k ± 0% 302k ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 302k ± 0% 302k ± 0% ~ (all equal)
name old allocs/entry new allocs/entry delta
WalkCaseFakeFS100k/rawfs-8 15.7 ± 0% 15.7 ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 27.5 ± 0% 26.1 ± 0% -5.09% (p=0.000 n=10+10)
name old ns/entry new ns/entry delta
WalkCaseFakeFS100k/rawfs-8 2.02k ± 1% 2.02k ± 2% ~ (p=0.163 n=9+10)
WalkCaseFakeFS100k/casefs-8 3.83k ± 5% 3.68k ± 1% -3.77% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
WalkCaseFakeFS100k/rawfs-8 89.2MB ± 0% 89.2MB ± 0% ~ (p=0.364 n=9+10)
WalkCaseFakeFS100k/casefs-8 164MB ± 0% 131MB ± 0% -19.97% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
WalkCaseFakeFS100k/rawfs-8 2.38M ± 0% 2.38M ± 0% ~ (all equal)
WalkCaseFakeFS100k/casefs-8 4.16M ± 0% 3.95M ± 0% -5.05% (p=0.000 n=10+10)
```
Since iterators must be released before committing or discarding a
transaction we have the pattern of both deferring a release plus doing
it manually. But we can't release twice because we track this with a
WaitGroup that will panic when there are more Done()s than Add()s. This
just adds a boolean to let an iterator keep track.
