106 lines
2.7 KiB
Go
106 lines
2.7 KiB
Go
// inomap translates (Dev, Flags, Ino) tuples to unique uint64
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// inode numbers.
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//
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// Format of the returned inode numbers:
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//
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// [spill bit = 0][15 bit namespace id][48 bit passthru inode number]
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// [spill bit = 1][63 bit spill inode number ]
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//
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// Each (Dev, Flags) tuple gets a namespace id assigned. The original inode
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// number is then passed through in the lower 48 bits.
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//
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// If namespace ids are exhaused, or the original id is larger than 48 bits,
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// the whole (Dev, Flags, Ino) tuple gets mapped in the spill map, and the
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// spill bit is set to 1.
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package inomap
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import (
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"log"
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"sync"
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"syscall"
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)
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const (
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// max value of 15 bit namespace id
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maxNamespaceId = 1<<15 - 1
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// max value of 48 bit passthru inode number
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maxPassthruIno = 1<<48 - 1
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// max value of 63 bit spill inode number
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maxSpillIno = 1<<63 - 1
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// bit 63 is used as the spill bit
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spillBit = 1 << 63
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)
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// InoMap stores the maps using for inode number translation.
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// See package comment for details.
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type InoMap struct {
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sync.Mutex
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// namespaces keeps the mapping of (Dev,Flags) tuples to
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// 15-bit identifiers (stored in an uint16 with the high bit always zero)
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namespaceMap map[namespaceData]uint16
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// spillNext is the next free namespace number in the namespaces map
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namespaceNext uint16
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// spill is used once the namespaces map is full
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spillMap map[QIno]uint64
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// spillNext is the next free inode number in the spill map
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spillNext uint64
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}
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// New returns a new InoMap.
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func New() *InoMap {
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return &InoMap{
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namespaceMap: make(map[namespaceData]uint16),
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namespaceNext: 0,
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spillMap: make(map[QIno]uint64),
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spillNext: 0,
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}
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}
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func (m *InoMap) spill(in QIno) (out uint64) {
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out, found := m.spillMap[in]
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if found {
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return out | spillBit
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}
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if m.spillNext >= maxSpillIno {
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log.Panicf("spillMap overflow: spillNext = 0x%x", m.spillNext)
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}
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out = m.spillNext
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m.spillNext++
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m.spillMap[in] = out
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return out | spillBit
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}
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// Translate maps the passed-in (device, inode) pair to a unique inode number.
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func (m *InoMap) Translate(in QIno) (out uint64) {
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m.Lock()
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defer m.Unlock()
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if in.Ino > maxPassthruIno {
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out = m.spill(in)
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return out
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}
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ns, found := m.namespaceMap[in.namespaceData]
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// Use existing namespace
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if found {
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out = uint64(ns)<<48 | in.Ino
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return out
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}
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// No free namespace slots?
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if m.namespaceNext >= maxNamespaceId {
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out = m.spill(in)
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return out
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}
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ns = m.namespaceNext
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m.namespaceNext++
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m.namespaceMap[in.namespaceData] = ns
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out = uint64(ns)<<48 | in.Ino
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return out
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}
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// TranslateStat translates the inode number contained in "st" if neccessary.
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// Convience wrapper around Translate().
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func (m *InoMap) TranslateStat(st *syscall.Stat_t) {
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in := QInoFromStat(st)
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st.Ino = m.Translate(in)
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}
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