214 lines
7.7 KiB
Go
214 lines
7.7 KiB
Go
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// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package vfs
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import (
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"sync/atomic"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/arch"
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"gvisor.dev/gvisor/pkg/sentry/context"
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"gvisor.dev/gvisor/pkg/sentry/memmap"
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"gvisor.dev/gvisor/pkg/sentry/usermem"
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"gvisor.dev/gvisor/pkg/waiter"
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)
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// A FileDescription represents an open file description, which is the entity
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// referred to by a file descriptor (POSIX.1-2017 3.258 "Open File
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// Description").
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//
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// FileDescriptions are reference-counted. Unless otherwise specified, all
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// FileDescription methods require that a reference is held.
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//
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// FileDescription is analogous to Linux's struct file.
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type FileDescription struct {
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// refs is the reference count. refs is accessed using atomic memory
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// operations.
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refs int64
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// vd is the filesystem location at which this FileDescription was opened.
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// A reference is held on vd. vd is immutable.
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vd VirtualDentry
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// impl is the FileDescriptionImpl associated with this Filesystem. impl is
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// immutable. This should be the last field in FileDescription.
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impl FileDescriptionImpl
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}
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// Init must be called before first use of fd. It takes references on mnt and
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// d.
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func (fd *FileDescription) Init(impl FileDescriptionImpl, mnt *Mount, d *Dentry) {
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fd.refs = 1
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fd.vd = VirtualDentry{
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mount: mnt,
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dentry: d,
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}
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fd.vd.IncRef()
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fd.impl = impl
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}
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// Impl returns the FileDescriptionImpl associated with fd.
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func (fd *FileDescription) Impl() FileDescriptionImpl {
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return fd.impl
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}
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// VirtualDentry returns the location at which fd was opened. It does not take
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// a reference on the returned VirtualDentry.
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func (fd *FileDescription) VirtualDentry() VirtualDentry {
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return fd.vd
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}
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// IncRef increments fd's reference count.
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func (fd *FileDescription) IncRef() {
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atomic.AddInt64(&fd.refs, 1)
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}
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// DecRef decrements fd's reference count.
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func (fd *FileDescription) DecRef() {
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if refs := atomic.AddInt64(&fd.refs, -1); refs == 0 {
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fd.impl.Release()
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fd.vd.DecRef()
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} else if refs < 0 {
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panic("FileDescription.DecRef() called without holding a reference")
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}
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}
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// FileDescriptionImpl contains implementation details for an FileDescription.
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// Implementations of FileDescriptionImpl should contain their associated
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// FileDescription by value as their first field.
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//
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// For all functions that return linux.Statx, Statx.Uid and Statx.Gid will
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// be interpreted as IDs in the root UserNamespace (i.e. as auth.KUID and
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// auth.KGID respectively).
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//
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// FileDescriptionImpl is analogous to Linux's struct file_operations.
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type FileDescriptionImpl interface {
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// Release is called when the associated FileDescription reaches zero
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// references.
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Release()
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// OnClose is called when a file descriptor representing the
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// FileDescription is closed. Note that returning a non-nil error does not
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// prevent the file descriptor from being closed.
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OnClose() error
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// StatusFlags returns file description status flags, as for
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// fcntl(F_GETFL).
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StatusFlags(ctx context.Context) (uint32, error)
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// SetStatusFlags sets file description status flags, as for
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// fcntl(F_SETFL).
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SetStatusFlags(ctx context.Context, flags uint32) error
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// Stat returns metadata for the file represented by the FileDescription.
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Stat(ctx context.Context, opts StatOptions) (linux.Statx, error)
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// SetStat updates metadata for the file represented by the
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// FileDescription.
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SetStat(ctx context.Context, opts SetStatOptions) error
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// StatFS returns metadata for the filesystem containing the file
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// represented by the FileDescription.
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StatFS(ctx context.Context) (linux.Statfs, error)
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// waiter.Waitable methods may be used to poll for I/O events.
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waiter.Waitable
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// PRead reads from the file into dst, starting at the given offset, and
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// returns the number of bytes read. PRead is permitted to return partial
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// reads with a nil error.
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PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts ReadOptions) (int64, error)
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// Read is similar to PRead, but does not specify an offset.
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//
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// For files with an implicit FileDescription offset (e.g. regular files),
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// Read begins at the FileDescription offset, and advances the offset by
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// the number of bytes read; note that POSIX 2.9.7 "Thread Interactions
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// with Regular File Operations" requires that all operations that may
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// mutate the FileDescription offset are serialized.
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Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error)
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// PWrite writes src to the file, starting at the given offset, and returns
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// the number of bytes written. PWrite is permitted to return partial
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// writes with a nil error.
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//
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// As in Linux (but not POSIX), if O_APPEND is in effect for the
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// FileDescription, PWrite should ignore the offset and append data to the
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// end of the file.
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PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts WriteOptions) (int64, error)
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// Write is similar to PWrite, but does not specify an offset, which is
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// implied as for Read.
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//
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// Write is a FileDescriptionImpl method, instead of a wrapper around
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// PWrite that uses a FileDescription offset, to make it possible for
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// remote filesystems to implement O_APPEND correctly (i.e. atomically with
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// respect to writers outside the scope of VFS).
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Write(ctx context.Context, src usermem.IOSequence, opts WriteOptions) (int64, error)
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// IterDirents invokes cb on each entry in the directory represented by the
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// FileDescription. If IterDirents has been called since the last call to
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// Seek, it continues iteration from the end of the last call.
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IterDirents(ctx context.Context, cb IterDirentsCallback) error
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// Seek changes the FileDescription offset (assuming one exists) and
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// returns its new value.
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//
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// For directories, if whence == SEEK_SET and offset == 0, the caller is
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// rewinddir(), such that Seek "shall also cause the directory stream to
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// refer to the current state of the corresponding directory" -
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// POSIX.1-2017.
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Seek(ctx context.Context, offset int64, whence int32) (int64, error)
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// Sync requests that cached state associated with the file represented by
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// the FileDescription is synchronized with persistent storage, and blocks
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// until this is complete.
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Sync(ctx context.Context) error
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// ConfigureMMap mutates opts to implement mmap(2) for the file. Most
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// implementations that support memory mapping can call
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// GenericConfigureMMap with the appropriate memmap.Mappable.
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ConfigureMMap(ctx context.Context, opts memmap.MMapOpts) error
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// Ioctl implements the ioctl(2) syscall.
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Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error)
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// TODO: extended attributes; file locking
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}
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// Dirent holds the information contained in struct linux_dirent64.
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type Dirent struct {
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// Name is the filename.
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Name string
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// Type is the file type, a linux.DT_* constant.
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Type uint8
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// Ino is the inode number.
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Ino uint64
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// Off is this Dirent's offset.
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Off int64
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}
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// IterDirentsCallback receives Dirents from FileDescriptionImpl.IterDirents.
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type IterDirentsCallback interface {
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// Handle handles the given iterated Dirent. It returns true if iteration
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// should continue, and false if FileDescriptionImpl.IterDirents should
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// terminate now and restart with the same Dirent the next time it is
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// called.
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Handle(dirent Dirent) bool
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}
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