889 lines
32 KiB
Go
889 lines
32 KiB
Go
// Copyright 2015 Google Inc. All Rights Reserved.
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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 fuse
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import (
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"fmt"
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"os"
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"time"
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"github.com/jacobsa/bazilfuse"
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"golang.org/x/net/context"
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)
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// An interface that must be implemented by file systems to be mounted with
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// FUSE. See also the comments on request and response structs.
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//
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// Not all methods need to have interesting implementations. Embed a field of
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// type fuseutil.NotImplementedFileSystem to inherit defaults that return
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// ENOSYS to the kernel.
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//
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// Must be safe for concurrent access via all methods.
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type FileSystem interface {
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// This method is called once when mounting the file system. It must succeed
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// in order for the mount to succeed.
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Init(
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ctx context.Context,
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req *InitRequest) (*InitResponse, error)
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///////////////////////////////////
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// Inodes
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///////////////////////////////////
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// Look up a child by name within a parent directory. The kernel calls this
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// when resolving user paths to dentry structs, which are then cached.
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LookUpInode(
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ctx context.Context,
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req *LookUpInodeRequest) (*LookUpInodeResponse, error)
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// Refresh the attributes for an inode whose ID was previously returned by
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// LookUpInode. The kernel calls this when the FUSE VFS layer's cache of
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// inode attributes is stale. This is controlled by the AttributesExpiration
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// field of responses to LookUp, etc.
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GetInodeAttributes(
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ctx context.Context,
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req *GetInodeAttributesRequest) (*GetInodeAttributesResponse, error)
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// Change attributes for an inode.
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//
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// The kernel calls this for obvious cases like chmod(2), and for less
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// obvious cases like ftrunctate(2).
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SetInodeAttributes(
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ctx context.Context,
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req *SetInodeAttributesRequest) (*SetInodeAttributesResponse, error)
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// Forget an inode ID previously issued (e.g. by LookUpInode or MkDir). The
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// kernel calls this when removing an inode from its internal caches.
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ForgetInode(
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ctx context.Context,
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req *ForgetInodeRequest) (*ForgetInodeResponse, error)
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///////////////////////////////////
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// Inode creation
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///////////////////////////////////
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// Create a directory inode as a child of an existing directory inode. The
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// kernel sends this in response to a mkdir(2) call.
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//
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// The kernel appears to verify the name doesn't already exist (mkdir calls
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// mkdirat calls user_path_create calls filename_create, which verifies:
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// http://goo.gl/FZpLu5). But volatile file systems and paranoid non-volatile
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// file systems should check for the reasons described below on CreateFile.
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MkDir(
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ctx context.Context,
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req *MkDirRequest) (*MkDirResponse, error)
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// Create a file inode and open it.
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//
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// The kernel calls this method when the user asks to open a file with the
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// O_CREAT flag and the kernel has observed that the file doesn't exist. (See
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// for example lookup_open, http://goo.gl/PlqE9d).
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//
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// However it's impossible to tell for sure that all kernels make this check
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// in all cases and the official fuse documentation is less than encouraging
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// (" the file does not exist, first create it with the specified mode, and
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// then open it"). Therefore file systems would be smart to be paranoid and
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// check themselves, returning EEXIST when the file already exists. This of
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// course particularly applies to file systems that are volatile from the
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// kernel's point of view.
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CreateFile(
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ctx context.Context,
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req *CreateFileRequest) (*CreateFileResponse, error)
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///////////////////////////////////
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// Inode destruction
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///////////////////////////////////
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// Unlink a directory from its parent. Because directories cannot have a link
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// count above one, this means the directory inode should be deleted as well
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// once the kernel calls ForgetInode.
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//
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// The file system is responsible for checking that the directory is empty.
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//
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// Sample implementation in ext2: ext2_rmdir (http://goo.gl/B9QmFf)
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RmDir(
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ctx context.Context,
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req *RmDirRequest) (*RmDirResponse, error)
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// Unlink a file from its parent. If this brings the inode's link count to
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// zero, the inode should be deleted once the kernel calls ForgetInode. It
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// may still be referenced before then if a user still has the file open.
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//
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// Sample implementation in ext2: ext2_unlink (http://goo.gl/hY6r6C)
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Unlink(
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ctx context.Context,
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req *UnlinkRequest) (*UnlinkResponse, error)
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///////////////////////////////////
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// Directory handles
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///////////////////////////////////
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// Open a directory inode.
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//
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// On Linux the kernel calls this method when setting up a struct file for a
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// particular inode with type directory, usually in response to an open(2)
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// call from a user-space process. On OS X it may not be called for every
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// open(2) (cf. https://github.com/osxfuse/osxfuse/issues/199).
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OpenDir(
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ctx context.Context,
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req *OpenDirRequest) (*OpenDirResponse, error)
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// Read entries from a directory previously opened with OpenDir.
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ReadDir(
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ctx context.Context,
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req *ReadDirRequest) (*ReadDirResponse, error)
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// Release a previously-minted directory handle. The kernel calls this when
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// there are no more references to an open directory: all file descriptors
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// are closed and all memory mappings are unmapped.
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//
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// The kernel guarantees that the handle ID will not be used in further calls
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// to the file system (unless it is reissued by the file system).
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ReleaseDirHandle(
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ctx context.Context,
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req *ReleaseDirHandleRequest) (*ReleaseDirHandleResponse, error)
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///////////////////////////////////
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// File handles
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///////////////////////////////////
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// Open a file inode.
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//
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// On Linux the kernel calls this method when setting up a struct file for a
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// particular inode with type file, usually in response to an open(2) call
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// from a user-space process. On OS X it may not be called for every open(2)
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// (cf.https://github.com/osxfuse/osxfuse/issues/199).
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OpenFile(
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ctx context.Context,
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req *OpenFileRequest) (*OpenFileResponse, error)
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// Read data from a file previously opened with CreateFile or OpenFile.
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//
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// Note that this method is not called for every call to read(2) by the end
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// user; some reads may be served by the page cache. See notes on Write for
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// more.
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ReadFile(
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ctx context.Context,
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req *ReadFileRequest) (*ReadFileResponse, error)
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// Write data to a file previously opened with CreateFile or OpenFile.
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//
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// When the user writes data using write(2), the write goes into the page
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// cache and the page is marked dirty. Later the kernel may write back the
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// page via the FUSE VFS layer, causing this method to be called:
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//
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// * The kernel calls address_space_operations::writepage when a dirty page
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// needs to be written to backing store (cf. http://goo.gl/Ezbewg). Fuse
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// sets this to fuse_writepage (cf. http://goo.gl/IeNvLT).
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//
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// * (http://goo.gl/Eestuy) fuse_writepage calls fuse_writepage_locked.
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//
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// * (http://goo.gl/RqYIxY) fuse_writepage_locked makes a write request to
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// the userspace server.
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//
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// Note that writes *will* be received before a call to Flush when closing
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// the file descriptor to which they were written:
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//
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// * (http://goo.gl/PheZjf) fuse_flush calls write_inode_now, which appears
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// to start a writeback in the background (it talks about a "flusher
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// thread").
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//
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// * (http://goo.gl/1IiepM) fuse_flush then calls fuse_sync_writes, which
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// "[waits] for all pending writepages on the inode to finish".
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//
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// * (http://goo.gl/zzvxWv) Only then does fuse_flush finally send the
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// flush request.
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//
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WriteFile(
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ctx context.Context,
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req *WriteFileRequest) (*WriteFileResponse, error)
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// Synchronize the current contents of an open file to storage.
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//
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// vfs.txt documents this as being called for by the fsync(2) system call
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// (cf. http://goo.gl/j9X8nB). Code walk for that case:
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//
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// * (http://goo.gl/IQkWZa) sys_fsync calls do_fsync, calls vfs_fsync, calls
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// vfs_fsync_range.
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//
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// * (http://goo.gl/5L2SMy) vfs_fsync_range calls f_op->fsync.
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//
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// Note that this is also called by fdatasync(2) (cf. http://goo.gl/01R7rF),
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// and may be called for msync(2) with the MS_SYNC flag (see the notes on
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// FlushFile).
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//
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// See also: FlushFile, which may perform a similar purpose when closing a
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// file (but which is not used in "real" file systems).
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SyncFile(
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ctx context.Context,
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req *SyncFileRequest) (*SyncFileResponse, error)
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// Flush the current state of an open file to storage upon closing a file
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// descriptor.
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//
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// vfs.txt documents this as being called for each close(2) system call (cf.
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// http://goo.gl/FSkbrq). Code walk for that case:
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//
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// * (http://goo.gl/e3lv0e) sys_close calls __close_fd, calls filp_close.
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// * (http://goo.gl/nI8fxD) filp_close calls f_op->flush (fuse_flush).
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//
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// But note that this is also called in other contexts where a file
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// descriptor is closed, such as dup2(2) (cf. http://goo.gl/NQDvFS). In the
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// case of close(2), a flush error is returned to the user. For dup2(2), it
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// is not.
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//
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// One potentially significant case where this may not be called is mmap'd
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// files, where the behavior is complicated:
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//
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// * munmap(2) does not cause flushes (cf. http://goo.gl/j8B9g0).
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//
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// * On OS X, if a user modifies a mapped file via the mapping before
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// closing the file with close(2), the WriteFile calls for the
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// modifications may not be received before the FlushFile request for the
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// close(2) (cf. http://goo.gl/kVmNcx).
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//
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// * However, even on OS X you can arrange for writes via a mapping to be
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// flushed by calling msync(2) followed by close(2). On OS X msync(2)
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// will cause a WriteFile to go through and close(2) will cause a
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// FlushFile as usual (cf. http://goo.gl/kVmNcx). On Linux, msync(2) does
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// nothing unless you set the MS_SYNC flag, in which case it causes a
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// SyncFile (cf. http://goo.gl/P3mErk).
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//
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// In summary: if you make data durable in both FlushFile and SyncFile, then
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// your users can get safe behavior from mapped files by calling msync(2)
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// with MS_SYNC, followed by munmap(2), followed by close(2). On Linux, the
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// msync(2) appears to be optional because close(2) implies dirty page
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// writeback (cf. http://goo.gl/HyzLTT).
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//
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// Because of cases like dup2(2), calls to FlushFile are not necessarily one
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// to one with calls to OpenFile. They should not be used for reference
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// counting, and the handle must remain valid even after the method is called
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// (use ReleaseFileHandle to dispose of it).
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//
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// Typical "real" file systems do not implement this, presumably relying on
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// the kernel to write out the page cache to the block device eventually.
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// They can get away with this because a later open(2) will see the same
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// data. A file system that writes to remote storage however probably wants
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// to at least schedule a real flush, and maybe do it immediately in order to
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// return any errors that occur.
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FlushFile(
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ctx context.Context,
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req *FlushFileRequest) (*FlushFileResponse, error)
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// Release a previously-minted file handle. The kernel calls this when there
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// are no more references to an open file: all file descriptors are closed
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// and all memory mappings are unmapped.
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//
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// The kernel guarantees that the handle ID will not be used in further calls
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// to the file system (unless it is reissued by the file system).
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ReleaseFileHandle(
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ctx context.Context,
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req *ReleaseFileHandleRequest) (*ReleaseFileHandleResponse, error)
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}
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////////////////////////////////////////////////////////////////////////
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// Simple types
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////////////////////////////////////////////////////////////////////////
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// A 64-bit number used to uniquely identify a file or directory in the file
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// system. File systems may mint inode IDs with any value except for
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// RootInodeID.
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//
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// This corresponds to struct inode::i_no in the VFS layer.
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// (Cf. http://goo.gl/tvYyQt)
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type InodeID uint64
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// A distinguished inode ID that identifies the root of the file system, e.g.
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// in a request to OpenDir or LookUpInode. Unlike all other inode IDs, which
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// are minted by the file system, the FUSE VFS layer may send a request for
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// this ID without the file system ever having referenced it in a previous
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// response.
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const RootInodeID = 1
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func init() {
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// Make sure the constant above is correct. We do this at runtime rather than
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// defining the constant in terms of bazilfuse.RootID for two reasons:
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//
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// 1. Users can more clearly see that the root ID is low and can therefore
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// be used as e.g. an array index, with space reserved up to the root.
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//
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// 2. The constant can be untyped and can therefore more easily be used as
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// an array index.
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//
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if RootInodeID != bazilfuse.RootID {
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panic(
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fmt.Sprintf(
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"Oops, RootInodeID is wrong: %v vs. %v",
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RootInodeID,
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bazilfuse.RootID))
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}
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}
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// Attributes for a file or directory inode. Corresponds to struct inode (cf.
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// http://goo.gl/tvYyQt).
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type InodeAttributes struct {
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Size uint64
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// The number of incoming hard links to this inode.
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Nlink uint64
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// The mode of the inode. This is exposed to the user in e.g. the result of
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// fstat(2).
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//
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// Note that in contrast to the defaults for FUSE, this package mounts file
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// systems in a manner such that the kernel checks inode permissions in the
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// standard posix way. This is implemented by setting the default_permissions
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// mount option (cf. http://goo.gl/1LxOop and http://goo.gl/1pTjuk).
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//
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// For example, in the case of mkdir:
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//
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// * (http://goo.gl/JkdxDI) sys_mkdirat calls inode_permission.
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//
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// * (...) inode_permission eventually calls do_inode_permission.
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//
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// * (http://goo.gl/aGCsmZ) calls i_op->permission, which is
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// fuse_permission (cf. http://goo.gl/VZ9beH).
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//
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// * (http://goo.gl/5kqUKO) fuse_permission doesn't do anything at all for
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// several code paths if FUSE_DEFAULT_PERMISSIONS is unset. In contrast,
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// if that flag *is* set, then it calls generic_permission.
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//
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Mode os.FileMode
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// Time information. See `man 2 stat` for full details.
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Atime time.Time // Time of last access
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Mtime time.Time // Time of last modification
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Ctime time.Time // Time of last modification to inode
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Crtime time.Time // Time of creation (OS X only)
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// Ownership information
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Uid uint32
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Gid uint32
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}
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// A generation number for an inode. Irrelevant for file systems that won't be
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// exported over NFS. For those that will and that reuse inode IDs when they
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// become free, the generation number must change when an ID is reused.
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//
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// This corresponds to struct inode::i_generation in the VFS layer.
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// (Cf. http://goo.gl/tvYyQt)
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//
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// Some related reading:
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//
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// http://fuse.sourceforge.net/doxygen/structfuse__entry__param.html
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// http://stackoverflow.com/q/11071996/1505451
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// http://goo.gl/CqvwyX
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// http://julipedia.meroh.net/2005/09/nfs-file-handles.html
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// http://goo.gl/wvo3MB
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//
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type GenerationNumber uint64
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// An opaque 64-bit number used to identify a particular open handle to a file
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// or directory.
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//
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// This corresponds to fuse_file_info::fh.
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type HandleID uint64
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// An offset into an open directory handle. This is opaque to FUSE, and can be
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// used for whatever purpose the file system desires. See notes on
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// ReadDirRequest.Offset for details.
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type DirOffset uint64
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// A header that is included with every request.
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type RequestHeader struct {
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// Credentials information for the process making the request.
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Uid uint32
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Gid uint32
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}
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// Information about a child inode within its parent directory. Shared by the
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// responses for LookUpInode, MkDir, CreateFile, etc. Consumed by the kernel in
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// order to set up a dcache entry.
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type ChildInodeEntry struct {
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// The ID of the child inode. The file system must ensure that the returned
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// inode ID remains valid until a later call to ForgetInode.
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Child InodeID
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// A generation number for this incarnation of the inode with the given ID.
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// See comments on type GenerationNumber for more.
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Generation GenerationNumber
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// Current attributes for the child inode.
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//
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// When creating a new inode, the file system is responsible for initializing
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// and recording (where supported) attributes like time information,
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// ownership information, etc.
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//
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// Ownership information in particular must be set to something reasonable or
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// by default root will own everything and unprivileged users won't be able
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// to do anything useful. In traditional file systems in the kernel, the
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// function inode_init_owner (http://goo.gl/5qavg8) contains the
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// standards-compliant logic for this.
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Attributes InodeAttributes
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// The FUSE VFS layer in the kernel maintains a cache of file attributes,
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// used whenever up to date information about size, mode, etc. is needed.
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//
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// For example, this is the abridged call chain for fstat(2):
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//
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// * (http://goo.gl/tKBH1p) fstat calls vfs_fstat.
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// * (http://goo.gl/3HeITq) vfs_fstat eventuall calls vfs_getattr_nosec.
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// * (http://goo.gl/DccFQr) vfs_getattr_nosec calls i_op->getattr.
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// * (http://goo.gl/dpKkst) fuse_getattr calls fuse_update_attributes.
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// * (http://goo.gl/yNlqPw) fuse_update_attributes uses the values in the
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// struct inode if allowed, otherwise calling out to the user-space code.
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//
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// In addition to obvious cases like fstat, this is also used in more subtle
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// cases like updating size information before seeking (http://goo.gl/2nnMFa)
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// or reading (http://goo.gl/FQSWs8).
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//
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// Most 'real' file systems do not set inode_operations::getattr, and
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// therefore vfs_getattr_nosec calls generic_fillattr which simply grabs the
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// information from the inode struct. This makes sense because these file
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// systems cannot spontaneously change; all modifications go through the
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// kernel which can update the inode struct as appropriate.
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//
|
|
// In contrast, a FUSE file system may have spontaneous changes, so it calls
|
|
// out to user space to fetch attributes. However this is expensive, so the
|
|
// FUSE layer in the kernel caches the attributes if requested.
|
|
//
|
|
// This field controls when the attributes returned in this response and
|
|
// stashed in the struct inode should be re-queried. Leave at the zero value
|
|
// to disable caching.
|
|
//
|
|
// More reading:
|
|
// http://stackoverflow.com/q/21540315/1505451
|
|
AttributesExpiration time.Time
|
|
|
|
// The time until which the kernel may maintain an entry for this name to
|
|
// inode mapping in its dentry cache. After this time, it will revalidate the
|
|
// dentry.
|
|
//
|
|
// As in the discussion of attribute caching above, unlike real file systems,
|
|
// FUSE file systems may spontaneously change their name -> inode mapping.
|
|
// Therefore the FUSE VFS layer uses dentry_operations::d_revalidate
|
|
// (http://goo.gl/dVea0h) to intercept lookups and revalidate by calling the
|
|
// user-space LookUpInode method. However the latter may be slow, so it
|
|
// caches the entries until the time defined by this field.
|
|
//
|
|
// Example code walk:
|
|
//
|
|
// * (http://goo.gl/M2G3tO) lookup_dcache calls d_revalidate if enabled.
|
|
// * (http://goo.gl/ef0Elu) fuse_dentry_revalidate just uses the dentry's
|
|
// inode if fuse_dentry_time(entry) hasn't passed. Otherwise it sends a
|
|
// lookup request.
|
|
//
|
|
// Leave at the zero value to disable caching.
|
|
//
|
|
// Beware: this value is ignored on OS X, where entry caching is disabled by
|
|
// default. See notes on MountConfig.EnableVnodeCaching for more.
|
|
EntryExpiration time.Time
|
|
}
|
|
|
|
////////////////////////////////////////////////////////////////////////
|
|
// Requests and responses
|
|
////////////////////////////////////////////////////////////////////////
|
|
|
|
type InitRequest struct {
|
|
Header RequestHeader
|
|
}
|
|
|
|
type InitResponse struct {
|
|
}
|
|
|
|
type LookUpInodeRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of the directory inode to which the child belongs.
|
|
Parent InodeID
|
|
|
|
// The name of the child of interest, relative to the parent. For example, in
|
|
// this directory structure:
|
|
//
|
|
// foo/
|
|
// bar/
|
|
// baz
|
|
//
|
|
// the file system may receive a request to look up the child named "bar" for
|
|
// the parent foo/.
|
|
Name string
|
|
}
|
|
|
|
type LookUpInodeResponse struct {
|
|
Entry ChildInodeEntry
|
|
}
|
|
|
|
type GetInodeAttributesRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The inode of interest.
|
|
Inode InodeID
|
|
}
|
|
|
|
type GetInodeAttributesResponse struct {
|
|
// Attributes for the inode, and the time at which they should expire. See
|
|
// notes on ChildInodeEntry.AttributesExpiration for more.
|
|
Attributes InodeAttributes
|
|
AttributesExpiration time.Time
|
|
}
|
|
|
|
type SetInodeAttributesRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The inode of interest.
|
|
Inode InodeID
|
|
|
|
// The attributes to modify, or nil for attributes that don't need a change.
|
|
Size *uint64
|
|
Mode *os.FileMode
|
|
Atime *time.Time
|
|
Mtime *time.Time
|
|
}
|
|
|
|
type SetInodeAttributesResponse struct {
|
|
// The new attributes for the inode, and the time at which they should
|
|
// expire. See notes on ChildInodeEntry.AttributesExpiration for more.
|
|
Attributes InodeAttributes
|
|
AttributesExpiration time.Time
|
|
}
|
|
|
|
type ForgetInodeRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The inode to be forgotten. The kernel guarantees that the node ID will not
|
|
// be used in further calls to the file system (unless it is reissued by the
|
|
// file system).
|
|
ID InodeID
|
|
}
|
|
|
|
type ForgetInodeResponse struct {
|
|
}
|
|
|
|
type MkDirRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of parent directory inode within which to create the child.
|
|
Parent InodeID
|
|
|
|
// The name of the child to create, and the mode with which to create it.
|
|
Name string
|
|
Mode os.FileMode
|
|
}
|
|
|
|
type MkDirResponse struct {
|
|
// Information about the inode that was created.
|
|
Entry ChildInodeEntry
|
|
}
|
|
|
|
type CreateFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of parent directory inode within which to create the child file.
|
|
Parent InodeID
|
|
|
|
// The name of the child to create, and the mode with which to create it.
|
|
Name string
|
|
Mode os.FileMode
|
|
|
|
// Flags for the open operation.
|
|
Flags bazilfuse.OpenFlags
|
|
}
|
|
|
|
type CreateFileResponse struct {
|
|
// Information about the inode that was created.
|
|
Entry ChildInodeEntry
|
|
|
|
// An opaque ID that will be echoed in follow-up calls for this file using
|
|
// the same struct file in the kernel. In practice this usually means
|
|
// follow-up calls using the file descriptor returned by open(2).
|
|
//
|
|
// The handle may be supplied in future calls to methods like ReadFile that
|
|
// accept a file handle. The file system must ensure this ID remains valid
|
|
// until a later call to ReleaseFileHandle.
|
|
Handle HandleID
|
|
}
|
|
|
|
type RmDirRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of parent directory inode, and the name of the directory being
|
|
// removed within it.
|
|
Parent InodeID
|
|
Name string
|
|
}
|
|
|
|
type UnlinkResponse struct {
|
|
}
|
|
|
|
type UnlinkRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of parent directory inode, and the name of the file being removed
|
|
// within it.
|
|
Parent InodeID
|
|
Name string
|
|
}
|
|
|
|
type RmDirResponse struct {
|
|
}
|
|
|
|
type OpenDirRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of the inode to be opened.
|
|
Inode InodeID
|
|
|
|
// Mode and options flags.
|
|
Flags bazilfuse.OpenFlags
|
|
}
|
|
|
|
type OpenDirResponse struct {
|
|
// An opaque ID that will be echoed in follow-up calls for this directory
|
|
// using the same struct file in the kernel. In practice this usually means
|
|
// follow-up calls using the file descriptor returned by open(2).
|
|
//
|
|
// The handle may be supplied in future calls to methods like ReadDir that
|
|
// accept a directory handle. The file system must ensure this ID remains
|
|
// valid until a later call to ReleaseDirHandle.
|
|
Handle HandleID
|
|
}
|
|
|
|
type ReadDirRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The directory inode that we are reading, and the handle previously
|
|
// returned by OpenDir when opening that inode.
|
|
Inode InodeID
|
|
Handle HandleID
|
|
|
|
// The offset within the directory at which to read.
|
|
//
|
|
// Warning: this field is not necessarily a count of bytes. Its legal values
|
|
// are defined by the results returned in ReadDirResponse. See the notes
|
|
// below and the notes on that struct.
|
|
//
|
|
// In the Linux kernel this ultimately comes from file::f_pos, which starts
|
|
// at zero and is set by llseek and by the final consumed result returned by
|
|
// each call to ReadDir:
|
|
//
|
|
// * (http://goo.gl/2nWJPL) iterate_dir, which is called by getdents(2) and
|
|
// readdir(2), sets dir_context::pos to file::f_pos before calling
|
|
// f_op->iterate, and then does the opposite assignment afterward.
|
|
//
|
|
// * (http://goo.gl/rTQVSL) fuse_readdir, which implements iterate for fuse
|
|
// directories, passes dir_context::pos as the offset to fuse_read_fill,
|
|
// which passes it on to user-space. fuse_readdir later calls
|
|
// parse_dirfile with the same context.
|
|
//
|
|
// * (http://goo.gl/vU5ukv) For each returned result (except perhaps the
|
|
// last, which may be truncated by the page boundary), parse_dirfile
|
|
// updates dir_context::pos with fuse_dirent::off.
|
|
//
|
|
// It is affected by the Posix directory stream interfaces in the following
|
|
// manner:
|
|
//
|
|
// * (http://goo.gl/fQhbyn, http://goo.gl/ns1kDF) opendir initially causes
|
|
// filepos to be set to zero.
|
|
//
|
|
// * (http://goo.gl/ezNKyR, http://goo.gl/xOmDv0) readdir allows the user
|
|
// to iterate through the directory one entry at a time. As each entry is
|
|
// consumed, its d_off field is stored in __dirstream::filepos.
|
|
//
|
|
// * (http://goo.gl/WEOXG8, http://goo.gl/rjSXl3) telldir allows the user
|
|
// to obtain the d_off field from the most recently returned entry.
|
|
//
|
|
// * (http://goo.gl/WG3nDZ, http://goo.gl/Lp0U6W) seekdir allows the user
|
|
// to seek backward to an offset previously returned by telldir. It
|
|
// stores the new offset in filepos, and calls llseek to update the
|
|
// kernel's struct file.
|
|
//
|
|
// * (http://goo.gl/gONQhz, http://goo.gl/VlrQkc) rewinddir allows the user
|
|
// to go back to the beginning of the directory, obtaining a fresh view.
|
|
// It updates filepos and calls llseek to update the kernel's struct
|
|
// file.
|
|
//
|
|
// Unfortunately, FUSE offers no way to intercept seeks
|
|
// (http://goo.gl/H6gEXa), so there is no way to cause seekdir or rewinddir
|
|
// to fail. Additionally, there is no way to distinguish an explicit
|
|
// rewinddir followed by readdir from the initial readdir, or a rewinddir
|
|
// from a seekdir to the value returned by telldir just after opendir.
|
|
//
|
|
// Luckily, Posix is vague about what the user will see if they seek
|
|
// backwards, and requires the user not to seek to an old offset after a
|
|
// rewind. The only requirement on freshness is that rewinddir results in
|
|
// something that looks like a newly-opened directory. So FUSE file systems
|
|
// may e.g. cache an entire fresh listing for each ReadDir with a zero
|
|
// offset, and return array offsets into that cached listing.
|
|
Offset DirOffset
|
|
|
|
// The maximum number of bytes to return in ReadDirResponse.Data. A smaller
|
|
// number is acceptable.
|
|
Size int
|
|
}
|
|
|
|
type ReadDirResponse struct {
|
|
// A buffer consisting of a sequence of FUSE directory entries in the format
|
|
// generated by fuse_add_direntry (http://goo.gl/qCcHCV), which is consumed
|
|
// by parse_dirfile (http://goo.gl/2WUmD2). Use fuseutil.AppendDirent to
|
|
// generate this data.
|
|
//
|
|
// The buffer must not exceed the length specified in ReadDirRequest.Size. It
|
|
// is okay for the final entry to be truncated; parse_dirfile copes with this
|
|
// by ignoring the partial record.
|
|
//
|
|
// Each entry returned exposes a directory offset to the user that may later
|
|
// show up in ReadDirRequest.Offset. See notes on that field for more
|
|
// information.
|
|
//
|
|
// An empty buffer indicates the end of the directory has been reached.
|
|
Data []byte
|
|
}
|
|
|
|
type ReleaseDirHandleRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The handle ID to be released. The kernel guarantees that this ID will not
|
|
// be used in further calls to the file system (unless it is reissued by the
|
|
// file system).
|
|
Handle HandleID
|
|
}
|
|
|
|
type ReleaseDirHandleResponse struct {
|
|
}
|
|
|
|
type OpenFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The ID of the inode to be opened.
|
|
Inode InodeID
|
|
|
|
// Mode and options flags.
|
|
Flags bazilfuse.OpenFlags
|
|
}
|
|
|
|
type OpenFileResponse struct {
|
|
// An opaque ID that will be echoed in follow-up calls for this file using
|
|
// the same struct file in the kernel. In practice this usually means
|
|
// follow-up calls using the file descriptor returned by open(2).
|
|
//
|
|
// The handle may be supplied in future calls to methods like ReadFile that
|
|
// accept a file handle. The file system must ensure this ID remains valid
|
|
// until a later call to ReleaseFileHandle.
|
|
Handle HandleID
|
|
}
|
|
|
|
type ReadFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The file inode that we are reading, and the handle previously returned by
|
|
// CreateFile or OpenFile when opening that inode.
|
|
Inode InodeID
|
|
Handle HandleID
|
|
|
|
// The range of the file to read.
|
|
//
|
|
// The FUSE documentation requires that exactly the number of bytes be
|
|
// returned, except in the case of EOF or error (http://goo.gl/ZgfBkF). This
|
|
// appears to be because it uses file mmapping machinery
|
|
// (http://goo.gl/SGxnaN) to read a page at a time. It appears to understand
|
|
// where EOF is by checking the inode size (http://goo.gl/0BkqKD), returned
|
|
// by a previous call to LookUpInode, GetInodeAttributes, etc.
|
|
Offset int64
|
|
Size int
|
|
}
|
|
|
|
type ReadFileResponse struct {
|
|
// The data read. If this is less than the requested size, it indicates EOF.
|
|
// An error should not be returned in this case.
|
|
Data []byte
|
|
}
|
|
|
|
type WriteFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The file inode that we are modifying, and the handle previously returned
|
|
// by CreateFile or OpenFile when opening that inode.
|
|
Inode InodeID
|
|
Handle HandleID
|
|
|
|
// The offset at which to write the data below.
|
|
//
|
|
// The man page for pwrite(2) implies that aside from changing the file
|
|
// handle's offset, using pwrite is equivalent to using lseek(2) and then
|
|
// write(2). The man page for lseek(2) says the following:
|
|
//
|
|
// "The lseek() function allows the file offset to be set beyond the end of
|
|
// the file (but this does not change the size of the file). If data is later
|
|
// written at this point, subsequent reads of the data in the gap (a "hole")
|
|
// return null bytes (aq\0aq) until data is actually written into the gap."
|
|
//
|
|
// It is therefore reasonable to assume that the kernel is looking for
|
|
// the following semantics:
|
|
//
|
|
// * If the offset is less than or equal to the current size, extend the
|
|
// file as necessary to fit any data that goes past the end of the file.
|
|
//
|
|
// * If the offset is greater than the current size, extend the file
|
|
// with null bytes until it is not, then do the above.
|
|
//
|
|
Offset int64
|
|
|
|
// The data to write.
|
|
//
|
|
// The FUSE documentation requires that exactly the number of bytes supplied
|
|
// be written, except on error (http://goo.gl/KUpwwn). This appears to be
|
|
// because it uses file mmapping machinery (http://goo.gl/SGxnaN) to write a
|
|
// page at a time.
|
|
Data []byte
|
|
}
|
|
|
|
type WriteFileResponse struct {
|
|
}
|
|
|
|
type SyncFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The file and handle being sync'd.
|
|
Inode InodeID
|
|
Handle HandleID
|
|
}
|
|
|
|
type SyncFileResponse struct {
|
|
}
|
|
|
|
type FlushFileRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The file and handle being flushed.
|
|
Inode InodeID
|
|
Handle HandleID
|
|
}
|
|
|
|
type FlushFileResponse struct {
|
|
}
|
|
|
|
type ReleaseFileHandleRequest struct {
|
|
Header RequestHeader
|
|
|
|
// The handle ID to be released. The kernel guarantees that this ID will not
|
|
// be used in further calls to the file system (unless it is reissued by the
|
|
// file system).
|
|
Handle HandleID
|
|
}
|
|
|
|
type ReleaseFileHandleResponse struct {
|
|
}
|