X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/29c5c69ef3c9ceadbea3085f2268bb5ed8496c04..8626abb0a44cfc303bef3552a7bc57163c79231a:/services/keepstore/volume_unix.go

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/volume_unix.go
index a7ad6f9e49..6c0f5c4e97 100644
--- a/services/keepstore/volume_unix.go
+++ b/services/keepstore/volume_unix.go
@@ -1,8 +1,7 @@
-// A UnixVolume is a Volume backed by a locally mounted disk.
-//
 package main
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -19,12 +18,15 @@ import (
 
 // A UnixVolume stores and retrieves blocks in a local directory.
 type UnixVolume struct {
-	root      string // path to the volume's root directory
-	serialize bool
-	readonly  bool
-	mutex     sync.Mutex
+	// path to the volume's root directory
+	root string
+	// something to lock during IO, typically a sync.Mutex (or nil
+	// to skip locking)
+	locker   sync.Locker
+	readonly bool
 }
 
+// Touch sets the timestamp for the given locator to the current time
 func (v *UnixVolume) Touch(loc string) error {
 	if v.readonly {
 		return MethodDisabledError
@@ -35,9 +37,9 @@ func (v *UnixVolume) Touch(loc string) error {
 		return err
 	}
 	defer f.Close()
-	if v.serialize {
-		v.mutex.Lock()
-		defer v.mutex.Unlock()
+	if v.locker != nil {
+		v.locker.Lock()
+		defer v.locker.Unlock()
 	}
 	if e := lockfile(f); e != nil {
 		return e
@@ -48,44 +50,59 @@ func (v *UnixVolume) Touch(loc string) error {
 	return syscall.Utime(p, &utime)
 }
 
+// Mtime returns the stored timestamp for the given locator.
 func (v *UnixVolume) Mtime(loc string) (time.Time, error) {
 	p := v.blockPath(loc)
-	if fi, err := os.Stat(p); err != nil {
+	fi, err := os.Stat(p)
+	if err != nil {
 		return time.Time{}, err
-	} else {
-		return fi.ModTime(), nil
 	}
+	return fi.ModTime(), nil
+}
+
+// Lock the locker (if one is in use), open the file for reading, and
+// call the given function if and when the file is ready to read.
+func (v *UnixVolume) getFunc(path string, fn func(io.Reader) error) error {
+	if v.locker != nil {
+		v.locker.Lock()
+		defer v.locker.Unlock()
+	}
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return fn(f)
+}
+
+// stat is os.Stat() with some extra sanity checks.
+func (v *UnixVolume) stat(path string) (os.FileInfo, error) {
+	stat, err := os.Stat(path)
+	if err == nil {
+		if stat.Size() < 0 {
+			err = os.ErrInvalid
+		} else if stat.Size() > BlockSize {
+			err = TooLongError
+		}
+	}
+	return stat, err
 }
 
 // Get retrieves a block identified by the locator string "loc", and
 // returns its contents as a byte slice.
 //
-// If the block could not be found, opened, or read, Get returns a nil
-// slice and whatever non-nil error was returned by Stat or ReadFile.
+// Get returns a nil buffer IFF it returns a non-nil error.
 func (v *UnixVolume) Get(loc string) ([]byte, error) {
 	path := v.blockPath(loc)
-	stat, err := os.Stat(path)
+	stat, err := v.stat(path)
 	if err != nil {
 		return nil, err
 	}
-	if stat.Size() < 0 {
-		return nil, os.ErrInvalid
-	} else if stat.Size() == 0 {
-		return bufs.Get(0), nil
-	} else if stat.Size() > BLOCKSIZE {
-		return nil, TooLongError
-	}
-	f, err := os.Open(path)
-	if err != nil {
-		return nil, err
-	}
-	defer f.Close()
 	buf := bufs.Get(int(stat.Size()))
-	if v.serialize {
-		v.mutex.Lock()
-		defer v.mutex.Unlock()
-	}
-	_, err = io.ReadFull(f, buf)
+	err = v.getFunc(path, func(rdr io.Reader) error {
+		_, err = io.ReadFull(rdr, buf)
+		return err
+	})
 	if err != nil {
 		bufs.Put(buf)
 		return nil, err
@@ -93,6 +110,51 @@ func (v *UnixVolume) Get(loc string) ([]byte, error) {
 	return buf, nil
 }
 
+// Compare returns nil if Get(loc) would return the same content as
+// expect. It is functionally equivalent to Get() followed by
+// bytes.Compare(), but uses less memory.
+func (v *UnixVolume) Compare(loc string, expect []byte) error {
+	path := v.blockPath(loc)
+	stat, err := v.stat(path)
+	if err != nil {
+		return err
+	}
+	bufLen := 1 << 20
+	if int64(bufLen) > stat.Size() {
+		bufLen = int(stat.Size())
+		if bufLen < 1 {
+			// len(buf)==0 would prevent us from handling
+			// empty files the same way as non-empty
+			// files, because reading 0 bytes at a time
+			// never reaches EOF.
+			bufLen = 1
+		}
+	}
+	cmp := expect
+	buf := make([]byte, bufLen)
+	return v.getFunc(path, func(rdr io.Reader) error {
+		// Loop invariants: all data read so far matched what
+		// we expected, and the first N bytes of cmp are
+		// expected to equal the next N bytes read from
+		// reader.
+		for {
+			n, err := rdr.Read(buf)
+			if n > len(cmp) || bytes.Compare(cmp[:n], buf[:n]) != 0 {
+				return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], buf[:n], rdr)
+			}
+			cmp = cmp[n:]
+			if err == io.EOF {
+				if len(cmp) != 0 {
+					return collisionOrCorrupt(loc[:32], expect[:len(expect)-len(cmp)], nil, nil)
+				}
+				return nil
+			} else if err != nil {
+				return err
+			}
+		}
+	})
+}
+
 // Put stores a block of data identified by the locator string
 // "loc".  It returns nil on success.  If the volume is full, it
 // returns a FullError.  If the write fails due to some other error,
@@ -118,9 +180,9 @@ func (v *UnixVolume) Put(loc string, block []byte) error {
 	}
 	bpath := v.blockPath(loc)
 
-	if v.serialize {
-		v.mutex.Lock()
-		defer v.mutex.Unlock()
+	if v.locker != nil {
+		v.locker.Lock()
+		defer v.locker.Unlock()
 	}
 	if _, err := tmpfile.Write(block); err != nil {
 		log.Printf("%s: writing to %s: %s\n", v, bpath, err)
@@ -235,6 +297,7 @@ func (v *UnixVolume) IndexTo(prefix string, w io.Writer) error {
 	}
 }
 
+// Delete deletes the block data from the unix storage
 func (v *UnixVolume) Delete(loc string) error {
 	// Touch() must be called before calling Write() on a block.  Touch()
 	// also uses lockfile().  This avoids a race condition between Write()
@@ -247,9 +310,9 @@ func (v *UnixVolume) Delete(loc string) error {
 	if v.readonly {
 		return MethodDisabledError
 	}
-	if v.serialize {
-		v.mutex.Lock()
-		defer v.mutex.Unlock()
+	if v.locker != nil {
+		v.locker.Lock()
+		defer v.locker.Unlock()
 	}
 	p := v.blockPath(loc)
 	f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
@@ -262,7 +325,7 @@ func (v *UnixVolume) Delete(loc string) error {
 	}
 	defer unlockfile(f)
 
-	// If the block has been PUT in the last blob_signature_ttl
+	// If the block has been PUT in the last blobSignatureTTL
 	// seconds, return success without removing the block. This
 	// protects data from garbage collection until it is no longer
 	// possible for clients to retrieve the unreferenced blocks
@@ -270,7 +333,7 @@ func (v *UnixVolume) Delete(loc string) error {
 	if fi, err := os.Stat(p); err != nil {
 		return err
 	} else {
-		if time.Since(fi.ModTime()) < blob_signature_ttl {
+		if time.Since(fi.ModTime()) < blobSignatureTTL {
 			return nil
 		}
 	}
@@ -290,7 +353,7 @@ func (v *UnixVolume) blockPath(loc string) string {
 }
 
 // IsFull returns true if the free space on the volume is less than
-// MIN_FREE_KILOBYTES.
+// MinFreeKilobytes.
 //
 func (v *UnixVolume) IsFull() (isFull bool) {
 	fullSymlink := v.root + "/full"
@@ -306,7 +369,7 @@ func (v *UnixVolume) IsFull() (isFull bool) {
 	}
 
 	if avail, err := v.FreeDiskSpace(); err == nil {
-		isFull = avail < MIN_FREE_KILOBYTES
+		isFull = avail < MinFreeKilobytes
 	} else {
 		log.Printf("%s: FreeDiskSpace: %s\n", v, err)
 		isFull = false
@@ -338,6 +401,7 @@ func (v *UnixVolume) String() string {
 	return fmt.Sprintf("[UnixVolume %s]", v.root)
 }
 
+// Writable returns false if all future Put, Mtime, and Delete calls are expected to fail.
 func (v *UnixVolume) Writable() bool {
 	return !v.readonly
 }