diff options
Diffstat (limited to 'pkg/sentry/fsimpl/kernfs/kernfs.go')
| -rw-r--r-- | pkg/sentry/fsimpl/kernfs/kernfs.go | 422 |
1 files changed, 0 insertions, 422 deletions
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go deleted file mode 100644 index bb12f39a2..000000000 --- a/pkg/sentry/fsimpl/kernfs/kernfs.go +++ /dev/null @@ -1,422 +0,0 @@ -// Copyright 2019 The gVisor Authors. -// -// Licensed under the Apache License, Version 2.0 (the "License"); -// you may not use this file except in compliance with the License. -// You may obtain a copy of the License at -// -// http://www.apache.org/licenses/LICENSE-2.0 -// -// Unless required by applicable law or agreed to in writing, software -// distributed under the License is distributed on an "AS IS" BASIS, -// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -// See the License for the specific language governing permissions and -// limitations under the License. - -// Package kernfs provides the tools to implement inode-based filesystems. -// Kernfs has two main features: -// -// 1. The Inode interface, which maps VFS2's path-based filesystem operations to -// specific filesystem nodes. Kernfs uses the Inode interface to provide a -// blanket implementation for the vfs.FilesystemImpl. Kernfs also serves as -// the synchronization mechanism for all filesystem operations by holding a -// filesystem-wide lock across all operations. -// -// 2. Various utility types which provide generic implementations for various -// parts of the Inode and vfs.FileDescription interfaces. Client filesystems -// based on kernfs can embed the appropriate set of these to avoid having to -// reimplement common filesystem operations. See inode_impl_util.go and -// fd_impl_util.go. -// -// Reference Model: -// -// Kernfs dentries represents named pointers to inodes. Dentries and inode have -// independent lifetimes and reference counts. A child dentry unconditionally -// holds a reference on its parent directory's dentry. A dentry also holds a -// reference on the inode it points to. Multiple dentries can point to the same -// inode (for example, in the case of hardlinks). File descriptors hold a -// reference to the dentry they're opened on. -// -// Dentries are guaranteed to exist while holding Filesystem.mu for -// reading. Dropping dentries require holding Filesystem.mu for writing. To -// queue dentries for destruction from a read critical section, see -// Filesystem.deferDecRef. -// -// Lock ordering: -// -// kernfs.Filesystem.mu -// kernfs.Dentry.dirMu -// vfs.VirtualFilesystem.mountMu -// vfs.Dentry.mu -// kernfs.Filesystem.droppedDentriesMu -// (inode implementation locks, if any) -package kernfs - -import ( - "fmt" - "sync/atomic" - - "gvisor.dev/gvisor/pkg/abi/linux" - "gvisor.dev/gvisor/pkg/refs" - "gvisor.dev/gvisor/pkg/sentry/context" - "gvisor.dev/gvisor/pkg/sentry/kernel/auth" - "gvisor.dev/gvisor/pkg/sentry/vfs" - "gvisor.dev/gvisor/pkg/sync" -) - -// FilesystemType implements vfs.FilesystemType. -type FilesystemType struct{} - -// Filesystem mostly implements vfs.FilesystemImpl for a generic in-memory -// filesystem. Concrete implementations are expected to embed this in their own -// Filesystem type. -type Filesystem struct { - vfsfs vfs.Filesystem - - droppedDentriesMu sync.Mutex - - // droppedDentries is a list of dentries waiting to be DecRef()ed. This is - // used to defer dentry destruction until mu can be acquired for - // writing. Protected by droppedDentriesMu. - droppedDentries []*vfs.Dentry - - // mu synchronizes the lifetime of Dentries on this filesystem. Holding it - // for reading guarantees continued existence of any resolved dentries, but - // the dentry tree may be modified. - // - // Kernfs dentries can only be DecRef()ed while holding mu for writing. For - // example: - // - // fs.mu.Lock() - // defer fs.mu.Unlock() - // ... - // dentry1.DecRef() - // defer dentry2.DecRef() // Ok, will run before Unlock. - // - // If discarding dentries in a read context, use Filesystem.deferDecRef. For - // example: - // - // fs.mu.RLock() - // fs.mu.processDeferredDecRefs() - // defer fs.mu.RUnlock() - // ... - // fs.deferDecRef(dentry) - mu sync.RWMutex - - // nextInoMinusOne is used to to allocate inode numbers on this - // filesystem. Must be accessed by atomic operations. - nextInoMinusOne uint64 -} - -// deferDecRef defers dropping a dentry ref until the next call to -// processDeferredDecRefs{,Locked}. See comment on Filesystem.mu. -// -// Precondition: d must not already be pending destruction. -func (fs *Filesystem) deferDecRef(d *vfs.Dentry) { - fs.droppedDentriesMu.Lock() - fs.droppedDentries = append(fs.droppedDentries, d) - fs.droppedDentriesMu.Unlock() -} - -// processDeferredDecRefs calls vfs.Dentry.DecRef on all dentries in the -// droppedDentries list. See comment on Filesystem.mu. -func (fs *Filesystem) processDeferredDecRefs() { - fs.mu.Lock() - fs.processDeferredDecRefsLocked() - fs.mu.Unlock() -} - -// Precondition: fs.mu must be held for writing. -func (fs *Filesystem) processDeferredDecRefsLocked() { - fs.droppedDentriesMu.Lock() - for _, d := range fs.droppedDentries { - d.DecRef() - } - fs.droppedDentries = fs.droppedDentries[:0] // Keep slice memory for reuse. - fs.droppedDentriesMu.Unlock() -} - -// Init initializes a kernfs filesystem. This should be called from during -// vfs.FilesystemType.NewFilesystem for the concrete filesystem embedding -// kernfs. -func (fs *Filesystem) Init(vfsObj *vfs.VirtualFilesystem) { - fs.vfsfs.Init(vfsObj, fs) -} - -// VFSFilesystem returns the generic vfs filesystem object. -func (fs *Filesystem) VFSFilesystem() *vfs.Filesystem { - return &fs.vfsfs -} - -// NextIno allocates a new inode number on this filesystem. -func (fs *Filesystem) NextIno() uint64 { - return atomic.AddUint64(&fs.nextInoMinusOne, 1) -} - -// These consts are used in the Dentry.flags field. -const ( - // Dentry points to a directory inode. - dflagsIsDir = 1 << iota - - // Dentry points to a symlink inode. - dflagsIsSymlink -) - -// Dentry implements vfs.DentryImpl. -// -// A kernfs dentry is similar to a dentry in a traditional filesystem: it's a -// named reference to an inode. A dentry generally lives as long as it's part of -// a mounted filesystem tree. Kernfs doesn't cache dentries once all references -// to them are removed. Dentries hold a single reference to the inode they point -// to, and child dentries hold a reference on their parent. -// -// Must be initialized by Init prior to first use. -type Dentry struct { - refs.AtomicRefCount - - vfsd vfs.Dentry - inode Inode - - refs uint64 - - // flags caches useful information about the dentry from the inode. See the - // dflags* consts above. Must be accessed by atomic ops. - flags uint32 - - // dirMu protects vfsd.children for directory dentries. - dirMu sync.Mutex -} - -// Init initializes this dentry. -// -// Precondition: Caller must hold a reference on inode. -// -// Postcondition: Caller's reference on inode is transferred to the dentry. -func (d *Dentry) Init(inode Inode) { - d.vfsd.Init(d) - d.inode = inode - ftype := inode.Mode().FileType() - if ftype == linux.ModeDirectory { - d.flags |= dflagsIsDir - } - if ftype == linux.ModeSymlink { - d.flags |= dflagsIsSymlink - } -} - -// VFSDentry returns the generic vfs dentry for this kernfs dentry. -func (d *Dentry) VFSDentry() *vfs.Dentry { - return &d.vfsd -} - -// isDir checks whether the dentry points to a directory inode. -func (d *Dentry) isDir() bool { - return atomic.LoadUint32(&d.flags)&dflagsIsDir != 0 -} - -// isSymlink checks whether the dentry points to a symlink inode. -func (d *Dentry) isSymlink() bool { - return atomic.LoadUint32(&d.flags)&dflagsIsSymlink != 0 -} - -// DecRef implements vfs.DentryImpl.DecRef. -func (d *Dentry) DecRef() { - d.AtomicRefCount.DecRefWithDestructor(d.destroy) -} - -// Precondition: Dentry must be removed from VFS' dentry cache. -func (d *Dentry) destroy() { - d.inode.DecRef() // IncRef from Init. - d.inode = nil - if parent := d.vfsd.Parent(); parent != nil { - parent.DecRef() // IncRef from Dentry.InsertChild. - } -} - -// InsertChild inserts child into the vfs dentry cache with the given name under -// this dentry. This does not update the directory inode, so calling this on -// it's own isn't sufficient to insert a child into a directory. InsertChild -// updates the link count on d if required. -// -// Precondition: d must represent a directory inode. -func (d *Dentry) InsertChild(name string, child *vfs.Dentry) { - d.dirMu.Lock() - d.insertChildLocked(name, child) - d.dirMu.Unlock() -} - -// insertChildLocked is equivalent to InsertChild, with additional -// preconditions. -// -// Precondition: d.dirMu must be locked. -func (d *Dentry) insertChildLocked(name string, child *vfs.Dentry) { - if !d.isDir() { - panic(fmt.Sprintf("InsertChild called on non-directory Dentry: %+v.", d)) - } - vfsDentry := d.VFSDentry() - vfsDentry.IncRef() // DecRef in child's Dentry.destroy. - vfsDentry.InsertChild(child, name) -} - -// The Inode interface maps filesystem-level operations that operate on paths to -// equivalent operations on specific filesystem nodes. -// -// The interface methods are groups into logical categories as sub interfaces -// below. Generally, an implementation for each sub interface can be provided by -// embedding an appropriate type from inode_impl_utils.go. The sub interfaces -// are purely organizational. Methods declared directly in the main interface -// have no generic implementations, and should be explicitly provided by the -// client filesystem. -// -// Generally, implementations are not responsible for tasks that are common to -// all filesystems. These include: -// -// - Checking that dentries passed to methods are of the appropriate file type. -// - Checking permissions. -// - Updating link and reference counts. -// -// Specific responsibilities of implementations are documented below. -type Inode interface { - // Methods related to reference counting. A generic implementation is - // provided by InodeNoopRefCount. These methods are generally called by the - // equivalent Dentry methods. - inodeRefs - - // Methods related to node metadata. A generic implementation is provided by - // InodeAttrs. - inodeMetadata - - // Method for inodes that represent symlink. InodeNotSymlink provides a - // blanket implementation for all non-symlink inodes. - inodeSymlink - - // Method for inodes that represent directories. InodeNotDirectory provides - // a blanket implementation for all non-directory inodes. - inodeDirectory - - // Method for inodes that represent dynamic directories and their - // children. InodeNoDynamicLookup provides a blanket implementation for all - // non-dynamic-directory inodes. - inodeDynamicLookup - - // Open creates a file description for the filesystem object represented by - // this inode. The returned file description should hold a reference on the - // inode for its lifetime. - // - // Precondition: !rp.Done(). vfsd.Impl() must be a kernfs Dentry. - Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, flags uint32) (*vfs.FileDescription, error) -} - -type inodeRefs interface { - IncRef() - DecRef() - TryIncRef() bool - // Destroy is called when the inode reaches zero references. Destroy release - // all resources (references) on objects referenced by the inode, including - // any child dentries. - Destroy() -} - -type inodeMetadata interface { - // CheckPermissions checks that creds may access this inode for the - // requested access type, per the the rules of - // fs/namei.c:generic_permission(). - CheckPermissions(creds *auth.Credentials, atx vfs.AccessTypes) error - - // Mode returns the (struct stat)::st_mode value for this inode. This is - // separated from Stat for performance. - Mode() linux.FileMode - - // Stat returns the metadata for this inode. This corresponds to - // vfs.FilesystemImpl.StatAt. - Stat(fs *vfs.Filesystem) linux.Statx - - // SetStat updates the metadata for this inode. This corresponds to - // vfs.FilesystemImpl.SetStatAt. - SetStat(fs *vfs.Filesystem, opts vfs.SetStatOptions) error -} - -// Precondition: All methods in this interface may only be called on directory -// inodes. -type inodeDirectory interface { - // The New{File,Dir,Node,Symlink} methods below should return a new inode - // hashed into this inode. - // - // These inode constructors are inode-level operations rather than - // filesystem-level operations to allow client filesystems to mix different - // implementations based on the new node's location in the - // filesystem. - - // HasChildren returns true if the directory inode has any children. - HasChildren() bool - - // NewFile creates a new regular file inode. - NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (*vfs.Dentry, error) - - // NewDir creates a new directory inode. - NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error) - - // NewLink creates a new hardlink to a specified inode in this - // directory. Implementations should create a new kernfs Dentry pointing to - // target, and update target's link count. - NewLink(ctx context.Context, name string, target Inode) (*vfs.Dentry, error) - - // NewSymlink creates a new symbolic link inode. - NewSymlink(ctx context.Context, name, target string) (*vfs.Dentry, error) - - // NewNode creates a new filesystem node for a mknod syscall. - NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (*vfs.Dentry, error) - - // Unlink removes a child dentry from this directory inode. - Unlink(ctx context.Context, name string, child *vfs.Dentry) error - - // RmDir removes an empty child directory from this directory - // inode. Implementations must update the parent directory's link count, - // if required. Implementations are not responsible for checking that child - // is a directory, checking for an empty directory. - RmDir(ctx context.Context, name string, child *vfs.Dentry) error - - // Rename is called on the source directory containing an inode being - // renamed. child should point to the resolved child in the source - // directory. If Rename replaces a dentry in the destination directory, it - // should return the replaced dentry or nil otherwise. - // - // Precondition: Caller must serialize concurrent calls to Rename. - Rename(ctx context.Context, oldname, newname string, child, dstDir *vfs.Dentry) (replaced *vfs.Dentry, err error) -} - -type inodeDynamicLookup interface { - // Lookup should return an appropriate dentry if name should resolve to a - // child of this dynamic directory inode. This gives the directory an - // opportunity on every lookup to resolve additional entries that aren't - // hashed into the directory. This is only called when the inode is a - // directory. If the inode is not a directory, or if the directory only - // contains a static set of children, the implementer can unconditionally - // return an appropriate error (ENOTDIR and ENOENT respectively). - // - // The child returned by Lookup will be hashed into the VFS dentry tree. Its - // lifetime can be controlled by the filesystem implementation with an - // appropriate implementation of Valid. - // - // Lookup returns the child with an extra reference and the caller owns this - // reference. - Lookup(ctx context.Context, name string) (*vfs.Dentry, error) - - // Valid should return true if this inode is still valid, or needs to - // be resolved again by a call to Lookup. - Valid(ctx context.Context) bool - - // IterDirents is used to iterate over dynamically created entries. It invokes - // cb on each entry in the directory represented by the FileDescription. - // 'offset' is the offset for the entire IterDirents call, which may include - // results from the caller. 'relOffset' is the offset inside the entries - // returned by this IterDirents invocation. In other words, - // 'offset+relOffset+1' is the value that should be set in vfs.Dirent.NextOff, - // while 'relOffset' is the place where iteration should start from. - IterDirents(ctx context.Context, callback vfs.IterDirentsCallback, offset, relOffset int64) (newOffset int64, err error) -} - -type inodeSymlink interface { - // Readlink resolves the target of a symbolic link. If an inode is not a - // symlink, the implementation should return EINVAL. - Readlink(ctx context.Context) (string, error) -} |