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