Line data Source code
1 : // Copyright 2012 The LevelDB-Go and Pebble Authors. All rights reserved. Use
2 : // of this source code is governed by a BSD-style license that can be found in
3 : // the LICENSE file.
4 :
5 : package vfs
6 :
7 : import (
8 : "io"
9 : "os"
10 : "path/filepath"
11 : "syscall"
12 :
13 : "github.com/cockroachdb/errors"
14 : "github.com/cockroachdb/errors/oserror"
15 : )
16 :
17 : // File is a readable, writable sequence of bytes.
18 : //
19 : // Typically, it will be an *os.File, but test code may choose to substitute
20 : // memory-backed implementations.
21 : //
22 : // Write-oriented operations (Write, Sync) must be called sequentially: At most
23 : // 1 call to Write or Sync may be executed at any given time.
24 : type File interface {
25 : io.Closer
26 : io.Reader
27 : io.ReaderAt
28 : // Unlike the specification for io.Writer.Write(), the vfs.File.Write()
29 : // method *is* allowed to modify the slice passed in, whether temporarily
30 : // or permanently. Callers of Write() need to take this into account.
31 : io.Writer
32 : // WriteAt() is only supported for files that were opened with FS.OpenReadWrite.
33 : io.WriterAt
34 :
35 : // Preallocate optionally preallocates storage for `length` at `offset`
36 : // within the file. Implementations may choose to do nothing.
37 : Preallocate(offset, length int64) error
38 : Stat() (os.FileInfo, error)
39 : Sync() error
40 :
41 : // SyncTo requests that a prefix of the file's data be synced to stable
42 : // storage. The caller passes provides a `length`, indicating how many bytes
43 : // to sync from the beginning of the file. SyncTo is a no-op for
44 : // directories, and therefore always returns false.
45 : //
46 : // SyncTo returns a fullSync return value, indicating one of two possible
47 : // outcomes.
48 : //
49 : // If fullSync is false, the first `length` bytes of the file was queued to
50 : // be synced to stable storage. The syncing of the file prefix may happen
51 : // asynchronously. No persistence guarantee is provided.
52 : //
53 : // If fullSync is true, the entirety of the file's contents were
54 : // synchronously synced to stable storage, and a persistence guarantee is
55 : // provided. In this outcome, any modified metadata for the file is not
56 : // guaranteed to be synced unless that metadata is needed in order to allow
57 : // a subsequent data retrieval to be correctly handled.
58 : SyncTo(length int64) (fullSync bool, err error)
59 :
60 : // SyncData requires that all written data be persisted. File metadata is
61 : // not required to be synced. Unsophisticated implementations may call Sync.
62 : SyncData() error
63 :
64 : // Prefetch signals the OS (on supported platforms) to fetch the next length
65 : // bytes in file (as returned by os.File.Fd()) after offset into cache. Any
66 : // subsequent reads in that range will not issue disk IO.
67 : Prefetch(offset int64, length int64) error
68 :
69 : // Fd returns the raw file descriptor when a File is backed by an *os.File.
70 : // It can be used for specific functionality like Prefetch.
71 : // Returns InvalidFd if not supported.
72 : Fd() uintptr
73 : }
74 :
75 : // InvalidFd is a special value returned by File.Fd() when the file is not
76 : // backed by an OS descriptor.
77 : // Note: the special value is consistent with what os.File implementation
78 : // returns on a nil receiver.
79 : const InvalidFd uintptr = ^(uintptr(0))
80 :
81 : // OpenOption provide an interface to do work on file handles in the Open()
82 : // call.
83 : type OpenOption interface {
84 : // Apply is called on the file handle after it's opened.
85 : Apply(File)
86 : }
87 :
88 : // FS is a namespace for files.
89 : //
90 : // The names are filepath names: they may be / separated or \ separated,
91 : // depending on the underlying operating system.
92 : type FS interface {
93 : // Create creates the named file for reading and writing. If a file
94 : // already exists at the provided name, it's removed first ensuring the
95 : // resulting file descriptor points to a new inode.
96 : Create(name string) (File, error)
97 :
98 : // Link creates newname as a hard link to the oldname file.
99 : Link(oldname, newname string) error
100 :
101 : // Open opens the named file for reading. openOptions provides
102 : Open(name string, opts ...OpenOption) (File, error)
103 :
104 : // OpenReadWrite opens the named file for reading and writing. If the file
105 : // does not exist, it is created.
106 : OpenReadWrite(name string, opts ...OpenOption) (File, error)
107 :
108 : // OpenDir opens the named directory for syncing.
109 : OpenDir(name string) (File, error)
110 :
111 : // Remove removes the named file or directory.
112 : Remove(name string) error
113 :
114 : // Remove removes the named file or directory and any children it
115 : // contains. It removes everything it can but returns the first error it
116 : // encounters.
117 : RemoveAll(name string) error
118 :
119 : // Rename renames a file. It overwrites the file at newname if one exists,
120 : // the same as os.Rename.
121 : Rename(oldname, newname string) error
122 :
123 : // ReuseForWrite attempts to reuse the file with oldname by renaming it to newname and opening
124 : // it for writing without truncation. It is acceptable for the implementation to choose not
125 : // to reuse oldname, and simply create the file with newname -- in this case the implementation
126 : // should delete oldname. If the caller calls this function with an oldname that does not exist,
127 : // the implementation may return an error.
128 : ReuseForWrite(oldname, newname string) (File, error)
129 :
130 : // MkdirAll creates a directory and all necessary parents. The permission
131 : // bits perm have the same semantics as in os.MkdirAll. If the directory
132 : // already exists, MkdirAll does nothing and returns nil.
133 : MkdirAll(dir string, perm os.FileMode) error
134 :
135 : // Lock locks the given file, creating the file if necessary, and
136 : // truncating the file if it already exists. The lock is an exclusive lock
137 : // (a write lock), but locked files should neither be read from nor written
138 : // to. Such files should have zero size and only exist to co-ordinate
139 : // ownership across processes.
140 : //
141 : // A nil Closer is returned if an error occurred. Otherwise, close that
142 : // Closer to release the lock.
143 : //
144 : // On Linux and OSX, a lock has the same semantics as fcntl(2)'s advisory
145 : // locks. In particular, closing any other file descriptor for the same
146 : // file will release the lock prematurely.
147 : //
148 : // Attempting to lock a file that is already locked by the current process
149 : // returns an error and leaves the existing lock untouched.
150 : //
151 : // Lock is not yet implemented on other operating systems, and calling it
152 : // will return an error.
153 : Lock(name string) (io.Closer, error)
154 :
155 : // List returns a listing of the given directory. The names returned are
156 : // relative to dir.
157 : List(dir string) ([]string, error)
158 :
159 : // Stat returns an os.FileInfo describing the named file.
160 : Stat(name string) (os.FileInfo, error)
161 :
162 : // PathBase returns the last element of path. Trailing path separators are
163 : // removed before extracting the last element. If the path is empty, PathBase
164 : // returns ".". If the path consists entirely of separators, PathBase returns a
165 : // single separator.
166 : PathBase(path string) string
167 :
168 : // PathJoin joins any number of path elements into a single path, adding a
169 : // separator if necessary.
170 : PathJoin(elem ...string) string
171 :
172 : // PathDir returns all but the last element of path, typically the path's directory.
173 : PathDir(path string) string
174 :
175 : // GetDiskUsage returns disk space statistics for the filesystem where
176 : // path is any file or directory within that filesystem.
177 : GetDiskUsage(path string) (DiskUsage, error)
178 : }
179 :
180 : // DiskUsage summarizes disk space usage on a filesystem.
181 : type DiskUsage struct {
182 : // Total disk space available to the current process in bytes.
183 : AvailBytes uint64
184 : // Total disk space in bytes.
185 : TotalBytes uint64
186 : // Used disk space in bytes.
187 : UsedBytes uint64
188 : }
189 :
190 : // Default is a FS implementation backed by the underlying operating system's
191 : // file system.
192 : var Default FS = defaultFS{}
193 :
194 : type defaultFS struct{}
195 :
196 : // wrapOSFile takes a standard library OS file and returns a vfs.File. f may be
197 : // nil, in which case wrapOSFile must not panic. In such cases, it's okay if the
198 : // returned vfs.File may panic if used.
199 1 : func wrapOSFile(f *os.File) File {
200 1 : // See the implementations in default_{linux,unix,windows}.go.
201 1 : return wrapOSFileImpl(f)
202 1 : }
203 :
204 1 : func (defaultFS) Create(name string) (File, error) {
205 1 : const openFlags = os.O_RDWR | os.O_CREATE | os.O_EXCL | syscall.O_CLOEXEC
206 1 :
207 1 : osFile, err := os.OpenFile(name, openFlags, 0666)
208 1 : // If the file already exists, remove it and try again.
209 1 : //
210 1 : // NB: We choose to remove the file instead of truncating it, despite the
211 1 : // fact that we can't do so atomically, because it's more resistant to
212 1 : // misuse when using hard links.
213 1 :
214 1 : // We must loop in case another goroutine/thread/process is also
215 1 : // attempting to create the a file at the same path.
216 1 : for oserror.IsExist(err) {
217 1 : if removeErr := os.Remove(name); removeErr != nil && !oserror.IsNotExist(removeErr) {
218 0 : return wrapOSFile(osFile), errors.WithStack(removeErr)
219 0 : }
220 1 : osFile, err = os.OpenFile(name, openFlags, 0666)
221 : }
222 1 : return wrapOSFile(osFile), errors.WithStack(err)
223 : }
224 :
225 1 : func (defaultFS) Link(oldname, newname string) error {
226 1 : return errors.WithStack(os.Link(oldname, newname))
227 1 : }
228 :
229 1 : func (defaultFS) Open(name string, opts ...OpenOption) (File, error) {
230 1 : osFile, err := os.OpenFile(name, os.O_RDONLY|syscall.O_CLOEXEC, 0)
231 1 : if err != nil {
232 0 : return nil, errors.WithStack(err)
233 0 : }
234 1 : file := wrapOSFile(osFile)
235 1 : for _, opt := range opts {
236 0 : opt.Apply(file)
237 0 : }
238 1 : return file, nil
239 : }
240 :
241 0 : func (defaultFS) OpenReadWrite(name string, opts ...OpenOption) (File, error) {
242 0 : osFile, err := os.OpenFile(name, os.O_RDWR|syscall.O_CLOEXEC|os.O_CREATE, 0666)
243 0 : if err != nil {
244 0 : return nil, errors.WithStack(err)
245 0 : }
246 0 : file := wrapOSFile(osFile)
247 0 : for _, opt := range opts {
248 0 : opt.Apply(file)
249 0 : }
250 0 : return file, nil
251 : }
252 :
253 1 : func (defaultFS) Remove(name string) error {
254 1 : return errors.WithStack(os.Remove(name))
255 1 : }
256 :
257 0 : func (defaultFS) RemoveAll(name string) error {
258 0 : return errors.WithStack(os.RemoveAll(name))
259 0 : }
260 :
261 1 : func (defaultFS) Rename(oldname, newname string) error {
262 1 : return errors.WithStack(os.Rename(oldname, newname))
263 1 : }
264 :
265 0 : func (fs defaultFS) ReuseForWrite(oldname, newname string) (File, error) {
266 0 : if err := fs.Rename(oldname, newname); err != nil {
267 0 : return nil, errors.WithStack(err)
268 0 : }
269 0 : f, err := os.OpenFile(newname, os.O_RDWR|os.O_CREATE|syscall.O_CLOEXEC, 0666)
270 0 : return wrapOSFile(f), errors.WithStack(err)
271 : }
272 :
273 1 : func (defaultFS) MkdirAll(dir string, perm os.FileMode) error {
274 1 : return errors.WithStack(os.MkdirAll(dir, perm))
275 1 : }
276 :
277 1 : func (defaultFS) List(dir string) ([]string, error) {
278 1 : f, err := os.Open(dir)
279 1 : if err != nil {
280 0 : return nil, err
281 0 : }
282 1 : defer f.Close()
283 1 : dirnames, err := f.Readdirnames(-1)
284 1 : return dirnames, errors.WithStack(err)
285 : }
286 :
287 1 : func (defaultFS) Stat(name string) (os.FileInfo, error) {
288 1 : finfo, err := os.Stat(name)
289 1 : return finfo, errors.WithStack(err)
290 1 : }
291 :
292 1 : func (defaultFS) PathBase(path string) string {
293 1 : return filepath.Base(path)
294 1 : }
295 :
296 1 : func (defaultFS) PathJoin(elem ...string) string {
297 1 : return filepath.Join(elem...)
298 1 : }
299 :
300 1 : func (defaultFS) PathDir(path string) string {
301 1 : return filepath.Dir(path)
302 1 : }
303 :
304 : type randomReadsOption struct{}
305 :
306 : // RandomReadsOption is an OpenOption that optimizes opened file handle for
307 : // random reads, by calling fadvise() with POSIX_FADV_RANDOM on Linux systems
308 : // to disable readahead.
309 : var RandomReadsOption OpenOption = &randomReadsOption{}
310 :
311 : // Apply implements the OpenOption interface.
312 1 : func (randomReadsOption) Apply(f File) {
313 1 : if fd := f.Fd(); fd != InvalidFd {
314 1 : _ = fadviseRandom(fd)
315 1 : }
316 : }
317 :
318 : type sequentialReadsOption struct{}
319 :
320 : // SequentialReadsOption is an OpenOption that optimizes opened file handle for
321 : // sequential reads, by calling fadvise() with POSIX_FADV_SEQUENTIAL on Linux
322 : // systems to enable readahead.
323 : var SequentialReadsOption OpenOption = &sequentialReadsOption{}
324 :
325 : // Apply implements the OpenOption interface.
326 1 : func (sequentialReadsOption) Apply(f File) {
327 1 : if fd := f.Fd(); fd != InvalidFd {
328 1 : _ = fadviseSequential(fd)
329 1 : }
330 : }
331 :
332 : // Copy copies the contents of oldname to newname. If newname exists, it will
333 : // be overwritten.
334 0 : func Copy(fs FS, oldname, newname string) error {
335 0 : return CopyAcrossFS(fs, oldname, fs, newname)
336 0 : }
337 :
338 : // CopyAcrossFS copies the contents of oldname on srcFS to newname dstFS. If
339 : // newname exists, it will be overwritten.
340 1 : func CopyAcrossFS(srcFS FS, oldname string, dstFS FS, newname string) error {
341 1 : src, err := srcFS.Open(oldname, SequentialReadsOption)
342 1 : if err != nil {
343 0 : return err
344 0 : }
345 1 : defer src.Close()
346 1 :
347 1 : dst, err := dstFS.Create(newname)
348 1 : if err != nil {
349 0 : return err
350 0 : }
351 1 : defer dst.Close()
352 1 :
353 1 : if _, err := io.Copy(dst, src); err != nil {
354 0 : return err
355 0 : }
356 1 : return dst.Sync()
357 : }
358 :
359 : // LimitedCopy copies up to maxBytes from oldname to newname. If newname
360 : // exists, it will be overwritten.
361 0 : func LimitedCopy(fs FS, oldname, newname string, maxBytes int64) error {
362 0 : src, err := fs.Open(oldname, SequentialReadsOption)
363 0 : if err != nil {
364 0 : return err
365 0 : }
366 0 : defer src.Close()
367 0 :
368 0 : dst, err := fs.Create(newname)
369 0 : if err != nil {
370 0 : return err
371 0 : }
372 0 : defer dst.Close()
373 0 :
374 0 : if _, err := io.Copy(dst, &io.LimitedReader{R: src, N: maxBytes}); err != nil {
375 0 : return err
376 0 : }
377 0 : return dst.Sync()
378 : }
379 :
380 : // LinkOrCopy creates newname as a hard link to the oldname file. If creating
381 : // the hard link fails, LinkOrCopy falls back to copying the file (which may
382 : // also fail if oldname doesn't exist or newname already exists).
383 1 : func LinkOrCopy(fs FS, oldname, newname string) error {
384 1 : err := fs.Link(oldname, newname)
385 1 : if err == nil {
386 1 : return nil
387 1 : }
388 : // Permit a handful of errors which we know won't be fixed by copying the
389 : // file. Note that we don't check for the specifics of the error code as it
390 : // isn't easy to do so in a portable manner. On Unix we'd have to check for
391 : // LinkError.Err == syscall.EXDEV. On Windows we'd have to check for
392 : // ERROR_NOT_SAME_DEVICE, ERROR_INVALID_FUNCTION, and
393 : // ERROR_INVALID_PARAMETER. Rather that such OS specific checks, we fall back
394 : // to always trying to copy if hard-linking failed.
395 0 : if oserror.IsExist(err) || oserror.IsNotExist(err) || oserror.IsPermission(err) {
396 0 : return err
397 0 : }
398 0 : return Copy(fs, oldname, newname)
399 : }
400 :
401 : // Root returns the base FS implementation, unwrapping all nested FSs that
402 : // expose an Unwrap method.
403 1 : func Root(fs FS) FS {
404 1 : type unwrapper interface {
405 1 : Unwrap() FS
406 1 : }
407 1 :
408 1 : for {
409 1 : u, ok := fs.(unwrapper)
410 1 : if !ok {
411 1 : break
412 : }
413 0 : fs = u.Unwrap()
414 : }
415 1 : return fs
416 : }
417 :
418 : // ErrUnsupported may be returned a FS when it does not support an operation.
419 : var ErrUnsupported = errors.New("pebble: not supported")
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