Struct LinkBacking 

pub struct LinkBacking<'a>(/* private fields */);

Remote display / control / valueAlarm metadata snapshot for a link, as exposed by pvxs’s pvalink lset metadata getters.

Mirrors the pvxs/ioc/pvalink_lset.cpp metadata getter set installed at pvxs/ioc/pvalink_lset.cpp:706-732: pvaGetDBFtype, pvaGetElements, pvaGetControlLimits, pvaGetGraphicLimits, pvaGetAlarmLimits, pvaGetPrecision, pvaGetUnits.

Every field is optional: pvxs’s getters read the cached NT structure with Value::as, which leaves the caller’s buffer unchanged when the sub-field is absent. None here means the remote NT value carried no such metadata — the record support then keeps its local/default metadata, exactly as the C path does. The link-backed metadata resolved for one snapshot build — the single channel through which a link’s target metadata can reach a served Snapshot.

The invariant it makes true by construction is a served snapshot’s link-backed metadata was resolved during THIS build. Three things enforce it, none of them a runtime check:

• the field is private and LinkBacking::resolved is pub(crate), so a crate outside epics-base-rs cannot make one and must go through PvDatabase::channel_snapshot_for_field;
• it borrows the resolve’s own output, so it cannot outlive the resolve and there is nowhere to store it — a stale value is unrepresentable;
• RecordInstance keeps no link-metadata map, so the consumer has no second source to read.

C needs no equivalent. dbLock.c:725-760 merges every DB_LINK-connected record into one lock set behind one recursive mutex, so get_units and its siblings call dbGetUnits/dbGetPrecision/… inline under the target’s lock (dbDbLink.c:240-261). The port has one RwLock per record and no lock sets, so it must resolve with no record lock held and hand the answer in; this type is that hand-off.

Implementations

impl<'a> LinkBacking<'a>

pub const fn none() -> Self

Nothing was resolved for this build: the record backs no field’s metadata with a link, or the caller is a path that serves only non-link-backed fields. Every lookup answers None, which serves each rset slot’s C seed — the same answer C’s untouched buffer gives for a CONSTANT link, an unresolvable target, or a link its DBLINK_FLAG_VISITED guard refused.

pub const fn resolved(resolved: &'a HashMap<String, LinkMetadata>) -> Self

What the links this record’s metadata is backed by resolved to, keyed by link field (INPA, INPB, …), resolved with no record lock held.

Trait Implementations

impl<'a> Clone for LinkBacking<'a>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Copy for LinkBacking<'a>