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fix(ecstore): keep O_DIRECT for eligible reads via native io_uring (rustfs/backlog#1102)
Wire ecstore's io_uring read backend to rustfs-uring's native aligned
O_DIRECT read (`read_at_direct`, merged in rustfs/uring#3), so an
O_DIRECT-eligible read keeps BOTH io_uring's async submission AND
O_DIRECT's page-cache bypass instead of trading one for the other.
`UringBackend::pread_bytes` now selects the read shape by a tiered,
per-disk-latched ladder — never a blanket downgrade:
1. io_uring latched off for this disk (backlog#1101) -> StdBackend.
2. O_DIRECT-eligible + native path usable -> pread_uring_direct: open
the file O_DIRECT, probe the device alignment once (cached), and
read via read_at_direct. Best path: async + no cache pollution.
3. O_DIRECT-eligible but the fs refused O_DIRECT earlier (latched)
-> StdBackend aligned path (which itself degrades to buffered).
4. non-O_DIRECT read -> buffered pread_uring.
Latching keeps a failure from being re-attempted per-read: an fs that
refuses O_DIRECT (EINVAL/EOPNOTSUPP on open) latches the native direct
path off for that disk; a restriction-class errno from the read latches
io_uring off wholesale (backlog#1101). Any other error falls back for
that one read without masking a genuine data problem as a permanent
downgrade. The alignment comes from the existing probe_direct_io_align
(statx STATX_DIOALIGN, default 4096) and is cached in a per-disk
OnceLock so the probe runs at most once.
This replaces the interim guard that routed every O_DIRECT-eligible read
to StdBackend (which disabled io_uring on the hottest shard reads); the
native path is now the default and StdBackend is only a fallback tier.
Bumps the rustfs-uring pin to the merged #3 commit.
Verified on a real Linux host (16-core, real io_uring + O_DIRECT):
cargo check --tests, clippy -D warnings, and disk::local tests all pass
(128 passed, 0 failed), including uring_preserves_o_direct_for_eligible_reads
across unaligned ranges.
Co-authored-by: heihutu <heihutu@gmail.com>