Nick Craig-Wood
b6ffdfa8e6
This commit introduced aux.go which unfortunately is illegal on windows.
e006d7c13f vfs: fix crash when multiple mounts or servers share the same VFS
Rename aux_test.go too to keep the pair together.
86 lines
2.3 KiB
Go
86 lines
2.3 KiB
Go
package vfs
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import "sync/atomic"
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// auxEntry associates an owner with a value attached to a node.
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type auxEntry struct {
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owner, value any
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}
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// aux holds auxiliary values attached to a node, keyed by owner.
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//
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// It is embedded in Dir and File to provide the Aux, SetAux, Sys and
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// SetSys methods of the Node interface.
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//
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// Reads are lock free. Writes copy the entry list, which is assumed
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// to be very short.
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type aux struct {
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entries atomic.Pointer[[]auxEntry]
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}
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// sysOwner is the owner Sys and SetSys attach their value under.
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type sysOwner struct{}
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// Aux returns the value attached to the node for owner, or nil if
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// none is attached.
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func (a *aux) Aux(owner any) any {
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if entries := a.entries.Load(); entries != nil {
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for _, entry := range *entries {
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if entry.owner == owner {
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return entry.value
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}
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}
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}
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return nil
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}
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// SetAux attaches value to the node for owner, replacing any value
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// owner attached before. Attaching nil removes owner's value.
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//
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// Values attached by different owners are independent, so multiple
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// users of a shared VFS do not conflict. Owner must be comparable and
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// unique to the user - a pointer to the user's filesystem struct is a
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// good choice.
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func (a *aux) SetAux(owner, value any) {
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for {
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old := a.entries.Load()
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var entries []auxEntry
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if old != nil {
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entries = make([]auxEntry, 0, len(*old)+1)
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for _, entry := range *old {
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if entry.owner != owner {
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entries = append(entries, entry)
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}
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}
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}
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if value != nil {
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entries = append(entries, auxEntry{owner: owner, value: value})
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}
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var next *[]auxEntry
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if len(entries) != 0 {
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next = &entries
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}
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if a.entries.CompareAndSwap(old, next) {
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return
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}
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}
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}
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// Sys returns the value set with SetSys (can be nil) - satisfies
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// os.FileInfo.
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//
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// This is what callers reading the node through os.FileInfo (e.g. the
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// NFS server library) will see. It is reserved for users which need
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// to control that; users caching their own data on the node should
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// use Aux and SetAux instead. As the VFS may be shared, the value
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// stored here should be derived from the node alone so that all users
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// store the same value.
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func (a *aux) Sys() any {
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return a.Aux(sysOwner{})
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}
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// SetSys sets the value returned by Sys - see Sys for the contract.
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func (a *aux) SetSys(x any) {
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a.SetAux(sysOwner{}, x)
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}
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