// 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 fuse import ( "context" "fmt" "log" "runtime" "strings" ) // Optional configuration accepted by Mount. type MountConfig struct { // The context from which every op read from the connetion by the sever // should inherit. If nil, context.Background() will be used. OpContext context.Context // If non-empty, the name of the file system as displayed by e.g. `mount`. // This is important because the `umount` command requires root privileges if // it doesn't agree with /etc/fstab. FSName string // Mount the file system in read-only mode. File modes will appear as normal, // but opening a file for writing and metadata operations like chmod, // chtimes, etc. will fail. ReadOnly bool // A logger to use for logging errors. All errors are logged, with the // exception of a few blacklisted errors that are expected. If nil, no error // logging is performed. ErrorLogger *log.Logger // A logger to use for logging debug information. If nil, no debug logging is // performed. DebugLogger *log.Logger // Linux only. OS X always behaves as if writeback caching is disabled. // // By default on Linux we allow the kernel to perform writeback caching // (cf. http://goo.gl/LdZzo1): // // * When the user calls write(2), the kernel sticks the user's data into // its page cache. Only later does it call through to the file system, // potentially after coalescing multiple small user writes. // // * The file system may receive multiple write ops from the kernel // concurrently if there is a lot of page cache data to flush. // // * Write performance may be significantly improved due to the user and // the kernel not waiting for serial round trips to the file system. This // is especially true if the user makes tiny writes. // // * close(2) (and anything else calling f_op->flush) causes all dirty // pages to be written out before it proceeds to send a FlushFileOp // (cf. https://goo.gl/TMrY6X). // // * Similarly, close(2) causes the kernel to send a setattr request // filling in the mtime if any dirty pages were flushed, since the time // at which the pages were written to the file system can't be trusted. // // * close(2) (and anything else calling f_op->flush) writes out all dirty // pages, then sends a setattr request with an appropriate mtime for // those writes if there were any, and only then proceeds to send a // flush. // // Code walk: // // * (https://goo.gl/zTIZQ9) fuse_flush calls write_inode_now before // calling the file system. The latter eventually calls into // __writeback_single_inode. // // * (https://goo.gl/L7Z2w5) __writeback_single_inode calls // do_writepages, which writes out any dirty pages. // // * (https://goo.gl/DOPgla) __writeback_single_inode later calls // write_inode, which calls into the superblock op struct's write_inode // member. For fuse, this is fuse_write_inode // (cf. https://goo.gl/eDSKOX). // // * (https://goo.gl/PbkGA1) fuse_write_inode calls fuse_flush_times. // // * (https://goo.gl/ig8x9V) fuse_flush_times sends a setttr request // for setting the inode's mtime. // // However, this brings along some caveats: // // * The file system must handle SetInodeAttributesOp or close(2) will fail, // due to the call chain into fuse_flush_times listed above. // // * The kernel caches mtime and ctime regardless of whether the file // system tells it to do so, disregarding the result of further getattr // requests (cf. https://goo.gl/3ZZMUw, https://goo.gl/7WtQUp). It // appears this may be true of the file size, too. Writeback caching may // therefore not be suitable for file systems where these attributes can // spontaneously change for reasons the kernel doesn't observe. See // http://goo.gl/V5WQCN for more discussion. // // Setting DisableWritebackCaching disables this behavior. Instead the file // system is called one or more times for each write(2), and the user's // syscall doesn't return until the file system returns. DisableWritebackCaching bool // OS X only. // // Normally on OS X we mount with the novncache option // (cf. http://goo.gl/1pTjuk), which disables entry caching in the kernel. // This is because osxfuse does not honor the entry expiration values we // return to it, instead caching potentially forever (cf. // http://goo.gl/8yR0Ie), and it is probably better to fail to cache than to // cache for too long, since the latter is more likely to hide consistency // bugs that are difficult to detect and diagnose. // // This field disables the use of novncache, restoring entry caching. Beware: // the value of ChildInodeEntry.EntryExpiration is ignored by the kernel, and // entries will be cached for an arbitrarily long time. EnableVnodeCaching bool // Linux only. // // Linux 4.20 introduced caching symlink targets in the page cache: // https://github.com/torvalds/linux/commit/5571f1e65486be025f73fa6aa30fb03725d362a2 // // This is not enabled by default because the old behavior masked a bug: // file systems could return any size in the inode attributes of // symlinks. After enabling caching, the specified size caps the symlink // target. EnableSymlinkCaching bool // Linux only. // // Tell the kernel to treat returning -ENOSYS on OpenFile as not needing // OpenFile calls at all (Linux >= 3.16): EnableNoOpenSupport bool // Linux only. // // Tell the kernel to treat returning -ENOSYS on OpenDir as not needing // OpenDir calls at all (Linux >= 5.1): EnableNoOpendirSupport bool // Tell the kernel to use READDIRPLUS. // Note that the implementation may still fall back to READDIR if the running // kernel doesn't have support for READDIRPLUS. UseReadDirPlus bool // Disable FUSE default permissions. // This is useful for situations where the backing data store (e.g., S3) doesn't // actually utilise any form of qualifiable UNIX permissions. DisableDefaultPermissions bool // Use vectored reads. // Vectored read allows file systems to avoid memory copying overhead if // the data is already in memory when they return it to FUSE. // When turned on, ReadFileOp.Dst is always nil and the FS must return data // being read from the file as a list of slices in ReadFileOp.Data. UseVectoredRead bool // OS X only. // // The name of the mounted volume, as displayed in the Finder. If empty, a // default name involving the string 'osxfuse' is used. VolumeName string // Additional key=value options to pass unadulterated to the underlying mount // command. See `man 8 mount`, the fuse documentation, etc. for // system-specific information. // // For expert use only! May invalidate other guarantees made in the // documentation for this package. Options map[string]string // Sets the filesystem type (third field in /etc/mtab). /etc/mtab and // /proc/mounts will show the filesystem type as fuse.. // If not set, /proc/mounts will show the filesystem type as fuse/fuseblk. Subtype string // Flag to enable async reads that are received from // the kernel EnableAsyncReads bool } // Create a map containing all of the key=value mount options to be given to // the mount helper. func (c *MountConfig) toMap() (opts map[string]string) { isDarwin := runtime.GOOS == "darwin" opts = make(map[string]string) // Enable permissions checking in the kernel. See the comments on // InodeAttributes.Mode. if !c.DisableDefaultPermissions { opts["default_permissions"] = "" } // HACK(jacobsa): Work around what appears to be a bug in systemd v219, as // shipped in Ubuntu 15.04, where it automatically unmounts any file system // that doesn't set an explicit name. // // When Ubuntu contains systemd v220, this workaround should be removed and // the systemd bug reopened if the problem persists. // // Cf. https://github.com/bazil/fuse/issues/89 // Cf. https://bugs.freedesktop.org/show_bug.cgi?id=90907 fsname := c.FSName if runtime.GOOS == "linux" && fsname == "" { fsname = "some_fuse_file_system" } // Special file system name? if fsname != "" { opts["fsname"] = fsname } subtype := c.Subtype if subtype != "" { opts["subtype"] = subtype } // Read only? if c.ReadOnly { opts["ro"] = "" } // Handle OS X options. if isDarwin { if !c.EnableVnodeCaching { opts["novncache"] = "" } if c.VolumeName != "" { // Cf. https://github.com/osxfuse/osxfuse/wiki/Mount-options#volname opts["volname"] = c.VolumeName } } // OS X: disable the use of "Apple Double" (._foo and .DS_Store) files, which // just add noise to debug output and can have significant cost on // network-based file systems. // // Cf. https://github.com/osxfuse/osxfuse/wiki/Mount-options if isDarwin { opts["noappledouble"] = "" } // Last but not least: other user-supplied options. for k, v := range c.Options { opts[k] = v } return opts } func escapeOptionsKey(s string) (res string) { res = s res = strings.Replace(res, `\`, `\\`, -1) res = strings.Replace(res, `,`, `\,`, -1) return res } func mapToOptionsString(opts map[string]string) string { var components []string for k, v := range opts { k = escapeOptionsKey(k) component := k if v != "" { component = fmt.Sprintf("%s=%s", k, v) } components = append(components, component) } return strings.Join(components, ",") } // Create an options string suitable for passing to the mount helper. func (c *MountConfig) toOptionsString() string { return mapToOptionsString(c.toMap()) }