Added op structs, to replace requests and responses for #3.

fuseops/simple_types.go

+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// 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 fuseops
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/jacobsa/bazilfuse"
+)
+
+// A 64-bit number used to uniquely identify a file or directory in the file
+// system. File systems may mint inode IDs with any value except for
+// RootInodeID.
+//
+// This corresponds to struct inode::i_no in the VFS layer.
+// (Cf. http://goo.gl/tvYyQt)
+type InodeID uint64
+
+// A distinguished inode ID that identifies the root of the file system, e.g.
+// in an OpenDirOp or LookUpInodeOp. Unlike all other inode IDs, which are
+// minted by the file system, the FUSE VFS layer may send a request for this ID
+// without the file system ever having referenced it in a previous response.
+const RootInodeID = 1
+
+func init() {
+	// Make sure the constant above is correct. We do this at runtime rather than
+	// defining the constant in terms of bazilfuse.RootID for two reasons:
+	//
+	//  1. Users can more clearly see that the root ID is low and can therefore
+	//     be used as e.g. an array index, with space reserved up to the root.
+	//
+	//  2. The constant can be untyped and can therefore more easily be used as
+	//     an array index.
+	//
+	if RootInodeID != bazilfuse.RootID {
+		panic(
+			fmt.Sprintf(
+				"Oops, RootInodeID is wrong: %v vs. %v",
+				RootInodeID,
+				bazilfuse.RootID))
+	}
+}
+
+// Attributes for a file or directory inode. Corresponds to struct inode (cf.
+// http://goo.gl/tvYyQt).
+type InodeAttributes struct {
+	Size uint64
+
+	// The number of incoming hard links to this inode.
+	Nlink uint64
+
+	// The mode of the inode. This is exposed to the user in e.g. the result of
+	// fstat(2).
+	//
+	// Note that in contrast to the defaults for FUSE, this package mounts file
+	// systems in a manner such that the kernel checks inode permissions in the
+	// standard posix way. This is implemented by setting the default_permissions
+	// mount option (cf. http://goo.gl/1LxOop and http://goo.gl/1pTjuk).
+	//
+	// For example, in the case of mkdir:
+	//
+	//  *  (http://goo.gl/JkdxDI) sys_mkdirat calls inode_permission.
+	//
+	//  *  (...) inode_permission eventually calls do_inode_permission.
+	//
+	//  *  (http://goo.gl/aGCsmZ) calls i_op->permission, which is
+	//     fuse_permission (cf. http://goo.gl/VZ9beH).
+	//
+	//  *  (http://goo.gl/5kqUKO) fuse_permission doesn't do anything at all for
+	//     several code paths if FUSE_DEFAULT_PERMISSIONS is unset. In contrast,
+	//     if that flag *is* set, then it calls generic_permission.
+	//
+	Mode os.FileMode
+
+	// Time information. See `man 2 stat` for full details.
+	Atime  time.Time // Time of last access
+	Mtime  time.Time // Time of last modification
+	Ctime  time.Time // Time of last modification to inode
+	Crtime time.Time // Time of creation (OS X only)
+
+	// Ownership information
+	Uid uint32
+	Gid uint32
+}
+
+// A generation number for an inode. Irrelevant for file systems that won't be
+// exported over NFS. For those that will and that reuse inode IDs when they
+// become free, the generation number must change when an ID is reused.
+//
+// This corresponds to struct inode::i_generation in the VFS layer.
+// (Cf. http://goo.gl/tvYyQt)
+//
+// Some related reading:
+//
+//     http://fuse.sourceforge.net/doxygen/structfuse__entry__param.html
+//     http://stackoverflow.com/q/11071996/1505451
+//     http://goo.gl/CqvwyX
+//     http://julipedia.meroh.net/2005/09/nfs-file-handles.html
+//     http://goo.gl/wvo3MB
+//
+type GenerationNumber uint64
+
+// An opaque 64-bit number used to identify a particular open handle to a file
+// or directory.
+//
+// This corresponds to fuse_file_info::fh.
+type HandleID uint64
+
+// An offset into an open directory handle. This is opaque to FUSE, and can be
+// used for whatever purpose the file system desires. See notes on
+// ReadDirOp.Offset for details.
+type DirOffset uint64
+
+// A header that is included with every op.
+type OpHeader struct {
+	// Credentials information for the process making the request.
+	Uid uint32
+	Gid uint32
+}
+
+// Information about a child inode within its parent directory. Shared by
+// LookUpInodeOp, MkDirOp, CreateFileOp, etc. Consumed by the kernel in order
+// to set up a dcache entry.
+type ChildInodeEntry struct {
+	// The ID of the child inode. The file system must ensure that the returned
+	// inode ID remains valid until a later ForgetInodeOp.
+	Child InodeID
+
+	// A generation number for this incarnation of the inode with the given ID.
+	// See comments on type GenerationNumber for more.
+	Generation GenerationNumber
+
+	// Current attributes for the child inode.
+	//
+	// When creating a new inode, the file system is responsible for initializing
+	// and recording (where supported) attributes like time information,
+	// ownership information, etc.
+	//
+	// Ownership information in particular must be set to something reasonable or
+	// by default root will own everything and unprivileged users won't be able
+	// to do anything useful. In traditional file systems in the kernel, the
+	// function inode_init_owner (http://goo.gl/5qavg8) contains the
+	// standards-compliant logic for this.
+	Attributes InodeAttributes
+
+	// The FUSE VFS layer in the kernel maintains a cache of file attributes,
+	// used whenever up to date information about size, mode, etc. is needed.
+	//
+	// For example, this is the abridged call chain for fstat(2):
+	//
+	//  *  (http://goo.gl/tKBH1p) fstat calls vfs_fstat.
+	//  *  (http://goo.gl/3HeITq) vfs_fstat eventuall calls vfs_getattr_nosec.
+	//  *  (http://goo.gl/DccFQr) vfs_getattr_nosec calls i_op->getattr.
+	//  *  (http://goo.gl/dpKkst) fuse_getattr calls fuse_update_attributes.
+	//  *  (http://goo.gl/yNlqPw) fuse_update_attributes uses the values in the
+	//     struct inode if allowed, otherwise calling out to the user-space code.
+	//
+	// In addition to obvious cases like fstat, this is also used in more subtle
+	// cases like updating size information before seeking (http://goo.gl/2nnMFa)
+	// or reading (http://goo.gl/FQSWs8).
+	//
+	// Most 'real' file systems do not set inode_operations::getattr, and
+	// therefore vfs_getattr_nosec calls generic_fillattr which simply grabs the
+	// information from the inode struct. This makes sense because these file
+	// systems cannot spontaneously change; all modifications go through the
+	// kernel which can update the inode struct as appropriate.
+	//
+	// 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
+}