shm

package
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 Go to latest Published: Jan 24, 2021 License: Apache-2.0, MIT Imports: 17 Imported by: 0

Documentation

Overview

Package shm implements sysv shared memory segments.

Known missing features:

  • SHM_LOCK/SHM_UNLOCK are no-ops. The sentry currently doesn't implement memory locking in general.
  • SHM_HUGETLB and related flags for shmget(2) are ignored. There's no easy way to implement hugetlb support on a per-map basis, and it has no impact on correctness.
  • SHM_NORESERVE for shmget(2) is ignored, the sentry doesn't implement swap so it's meaningless to reserve space for swap.
  • No per-process segment size enforcement. This feature probably isn't used much anyways, since Linux sets the per-process limits to the system-wide limits by default.

Lock ordering: mm.mappingMu -> shm registry lock -> shm lock

Index

Constants

View Source 
const ShmenableLogging = true

enableLogging indicates whether reference-related events should be logged (with stack traces). This is false by default and should only be set to true for debugging purposes, as it can generate an extremely large amount of output and drastically degrade performance.

Variables

This section is empty.

Functions

This section is empty.

Types

type AttachOpts 

type AttachOpts struct {
	Execute  bool
	Readonly bool
	Remap    bool
}

AttachOpts describes various flags passed to shmat(2).

type ID 

type ID int32

ID represents the opaque handle for a shm segment. Analogous to an fd.

type Key 

type Key int32

Key represents a shm segment key. Analogous to a file name.

type Registry 

type Registry struct {
	// contains filtered or unexported fields
}

Registry tracks all shared memory segments in an IPC namespace. The registry provides the mechanisms for creating and finding segments, and reporting global shm parameters.

+stateify savable

func NewRegistry 

func NewRegistry(userNS *auth.UserNamespace) *Registry

NewRegistry creates a new shm registry.

func (*Registry) FindByID 

func (r *Registry) FindByID(id ID) *Shm

FindByID looks up a segment given an ID.

FindByID returns a reference on Shm.

func (*Registry) FindOrCreate 

func (r *Registry) FindOrCreate(ctx context.Context, pid int32, key Key, size uint64, mode linux.FileMode, private, create, exclusive bool) (*Shm, error)

FindOrCreate looks up or creates a segment in the registry. It's functionally analogous to open(2).

FindOrCreate returns a reference on Shm.

func (*Registry) IPCInfo 

func (r *Registry) IPCInfo() *linux.ShmParams

IPCInfo reports global parameters for sysv shared memory segments on this system. See shmctl(IPC_INFO).

func (*Registry) Release 

func (r *Registry) Release(ctx context.Context)

Release drops the self-reference of each active shm segment in the registry. It is called when the kernel.IPCNamespace containing r is being destroyed.

func (*Registry) ShmInfo 

func (r *Registry) ShmInfo() *linux.ShmInfo

ShmInfo reports linux-specific global parameters for sysv shared memory segments on this system. See shmctl(SHM_INFO).

func (*Registry) StateFields 

func (r *Registry) StateFields() []string

func (*Registry) StateLoad 

func (r *Registry) StateLoad(stateSourceObject state.Source)

func (*Registry) StateSave 

func (r *Registry) StateSave(stateSinkObject state.Sink)

func (*Registry) StateTypeName 

func (r *Registry) StateTypeName() string

type Shm 

type Shm struct {
	// ShmRefs tracks the number of references to this segment.
	//
	// A segment holds a reference to itself until it is marked for
	// destruction.
	//
	// In addition to direct users, the MemoryManager will hold references
	// via MappingIdentity.
	ShmRefs

	// ID is the kernel identifier for this segment. Immutable.
	ID ID
	// contains filtered or unexported fields
}

Shm represents a single shared memory segment.

Shm segments are backed directly by an allocation from platform memory. Segments are always mapped as a whole, greatly simplifying how mappings are tracked. However note that mremap and munmap calls may cause the vma for a segment to become fragmented; which requires special care when unmapping a segment. See mm/shm.go.

Segments persist until they are explicitly marked for destruction via MarkDestroyed().

Shm implements memmap.Mappable and memmap.MappingIdentity.

+stateify savable 

var Shmobj *Shm

obj is used to customize logging. Note that we use a pointer to T so that we do not copy the entire object when passed as a format parameter.

func (*Shm) AddMapping 

func (s *Shm) AddMapping(ctx context.Context, _ memmap.MappingSpace, _ usermem.AddrRange, _ uint64, _ bool) error

AddMapping implements memmap.Mappable.AddMapping.

func (*Shm) ConfigureAttach 

func (s *Shm) ConfigureAttach(ctx context.Context, addr usermem.Addr, opts AttachOpts) (memmap.MMapOpts, error)

ConfigureAttach creates an mmap configuration for the segment with the requested attach options.

Postconditions: The returned MMapOpts are valid only as long as a reference continues to be held on s.

func (*Shm) CopyMapping 

func (*Shm) CopyMapping(context.Context, memmap.MappingSpace, usermem.AddrRange, usermem.AddrRange, uint64, bool) error

CopyMapping implements memmap.Mappable.CopyMapping.

func (*Shm) DecRef 

func (s *Shm) DecRef(ctx context.Context)

DecRef drops a reference on s.

Precondition: Caller must not hold s.mu.

func (*Shm) DeviceID 

func (s *Shm) DeviceID() uint64

DeviceID implements memmap.MappingIdentity.DeviceID.

func (*Shm) EffectiveSize 

func (s *Shm) EffectiveSize() uint64

EffectiveSize returns the size of the underlying shared memory segment. This may be larger than the requested size at creation, due to rounding to page boundaries.

func (*Shm) IPCStat 

func (s *Shm) IPCStat(ctx context.Context) (*linux.ShmidDS, error)

IPCStat returns information about a shm. See shmctl(IPC_STAT).

func (*Shm) InodeID 

func (s *Shm) InodeID() uint64

InodeID implements memmap.MappingIdentity.InodeID.

func (*Shm) InvalidateUnsavable 

func (s *Shm) InvalidateUnsavable(ctx context.Context) error

InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.

func (*Shm) MappedName 

func (s *Shm) MappedName(ctx context.Context) string

MappedName implements memmap.MappingIdentity.MappedName.

func (*Shm) MarkDestroyed 

func (s *Shm) MarkDestroyed(ctx context.Context)

MarkDestroyed marks a segment for destruction. The segment is actually destroyed once it has no references. MarkDestroyed may be called multiple times, and is safe to call after a segment has already been destroyed. See shmctl(IPC_RMID).

func (*Shm) Msync 

func (s *Shm) Msync(context.Context, memmap.MappableRange) error

Msync implements memmap.MappingIdentity.Msync. Msync is a no-op for shm segments.

func (*Shm) RemoveMapping 

func (s *Shm) RemoveMapping(ctx context.Context, _ memmap.MappingSpace, _ usermem.AddrRange, _ uint64, _ bool)

RemoveMapping implements memmap.Mappable.RemoveMapping.

func (*Shm) Set 

func (s *Shm) Set(ctx context.Context, ds *linux.ShmidDS) error

Set modifies attributes for a segment. See shmctl(IPC_SET).

func (*Shm) StateFields 

func (s *Shm) StateFields() []string

func (*Shm) StateLoad 

func (s *Shm) StateLoad(stateSourceObject state.Source)

func (*Shm) StateSave 

func (s *Shm) StateSave(stateSinkObject state.Sink)

func (*Shm) StateTypeName 

func (s *Shm) StateTypeName() string

func (*Shm) Translate 

func (s *Shm) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error)

Translate implements memmap.Mappable.Translate.

type ShmRefs 

type ShmRefs struct {
	// contains filtered or unexported fields
}

Refs implements refs.RefCounter. It keeps a reference count using atomic operations and calls the destructor when the count reaches zero.

+stateify savable

func (*ShmRefs) DecRef 

func (r *ShmRefs) DecRef(destroy func())

DecRef implements refs.RefCounter.DecRef.

Note that speculative references are counted here. Since they were added prior to real references reaching zero, they will successfully convert to real references. In other words, we see speculative references only in the following case: 

A: TryIncRef [speculative increase => sees non-negative references]
B: DecRef [real decrease]
A: TryIncRef [transform speculative to real]

func (*ShmRefs) IncRef 

func (r *ShmRefs) IncRef()

IncRef implements refs.RefCounter.IncRef.

func (*ShmRefs) InitRefs 

func (r *ShmRefs) InitRefs()

InitRefs initializes r with one reference and, if enabled, activates leak checking.

func (*ShmRefs) LeakMessage 

func (r *ShmRefs) LeakMessage() string

LeakMessage implements refsvfs2.CheckedObject.LeakMessage.

func (*ShmRefs) LogRefs 

func (r *ShmRefs) LogRefs() bool

LogRefs implements refsvfs2.CheckedObject.LogRefs.

func (*ShmRefs) ReadRefs 

func (r *ShmRefs) ReadRefs() int64

ReadRefs returns the current number of references. The returned count is inherently racy and is unsafe to use without external synchronization.

func (*ShmRefs) RefType 

func (r *ShmRefs) RefType() string

RefType implements refsvfs2.CheckedObject.RefType.

func (*ShmRefs) StateFields 

func (r *ShmRefs) StateFields() []string

func (*ShmRefs) StateLoad 

func (r *ShmRefs) StateLoad(stateSourceObject state.Source)

func (*ShmRefs) StateSave 

func (r *ShmRefs) StateSave(stateSinkObject state.Sink)

func (*ShmRefs) StateTypeName 

func (r *ShmRefs) StateTypeName() string

func (*ShmRefs) TryIncRef 

func (r *ShmRefs) TryIncRef() bool

TryIncRef implements refs.RefCounter.TryIncRef.

To do this safely without a loop, a speculative reference is first acquired on the object. This allows multiple concurrent TryIncRef calls to distinguish other TryIncRef calls from genuine references held.

Source Files

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