fusefrontend: rewrite Lseek SEEK_DATA / SEEK_HOLE
In response to the discussion of the xfstests mailing list [1], I looked at the Lseek implementation, which was naive and did not handle all cases correctly. The new implementation aligns the returned values to 4096 bytes as most callers expect. A lot of tests are added to verify that we handle all cases correctly now. [1]: https://www.spinics.net/lists/fstests/msg16554.html
This commit is contained in:
Jakob Unterwurzacher
parent
c1d7e38761
commit
738a9e006a
@ -4,6 +4,7 @@ package fusefrontend
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import (
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"context"
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"runtime"
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"syscall"
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"github.com/hanwen/go-fuse/v2/fs"
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@ -57,12 +58,71 @@ func (f *File) zeroPad(plainSize uint64) syscall.Errno {
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}
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// Lseek - FUSE call.
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//
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// Looking at
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// fuse_file_llseek @ https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/fs/fuse/file.c?h=v5.12.7#n2634
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// this function is only called for SEEK_HOLE & SEEK_DATA.
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func (f *File) Lseek(ctx context.Context, off uint64, whence uint32) (uint64, syscall.Errno) {
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cipherOff := f.rootNode.contentEnc.PlainSizeToCipherSize(off)
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newCipherOff, err := syscall.Seek(f.intFd(), int64(cipherOff), int(whence))
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const (
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SEEK_DATA = 3 // find next data segment at or above `off`
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SEEK_HOLE = 4 // find next hole at or above `off`
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// On error, we return -1 as the offset as per man lseek.
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MinusOne = ^uint64(0)
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)
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if whence != SEEK_DATA && whence != SEEK_HOLE {
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tlog.Warn.Printf("BUG: Lseek was called with whence=%d. This is not supported!", whence)
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return 0, syscall.EINVAL
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}
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if runtime.GOOS != "linux" {
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// MacOS has broken (different?) SEEK_DATA / SEEK_HOLE semantics, see
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// https://lists.gnu.org/archive/html/bug-gnulib/2018-09/msg00051.html
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tlog.Warn.Printf("buggy on non-linux platforms, disabling SEEK_DATA & SEEK_HOLE")
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return MinusOne, syscall.ENOSYS
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}
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// We will need the file size
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var st syscall.Stat_t
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err := syscall.Fstat(f.intFd(), &st)
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if err != nil {
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return 0, fs.ToErrno(err)
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}
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newOff := f.contentEnc.CipherSizeToPlainSize(uint64(newCipherOff))
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return newOff, 0
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fileSize := st.Size
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// Better safe than sorry. The logic is only tested for 4k blocks.
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if st.Blksize != 4096 {
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tlog.Warn.Printf("unsupported block size of %d bytes, disabling SEEK_DATA & SEEK_HOLE", st.Blksize)
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return MinusOne, syscall.ENOSYS
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}
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// man lseek: offset beyond end of file -> ENXIO
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if f.rootNode.contentEnc.PlainOffToCipherOff(off) >= uint64(fileSize) {
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return MinusOne, syscall.ENXIO
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}
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// Round down to start of block:
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cipherOff := f.rootNode.contentEnc.BlockNoToCipherOff(f.rootNode.contentEnc.PlainOffToBlockNo(off))
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newCipherOff, err := syscall.Seek(f.intFd(), int64(cipherOff), int(whence))
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if err != nil {
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return MinusOne, fs.ToErrno(err)
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}
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// already in data/hole => return original offset
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if newCipherOff == int64(cipherOff) {
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return off, 0
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}
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// If there is no further hole, SEEK_HOLE returns the file size
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// (SEEK_DATA returns ENXIO in this case).
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if whence == SEEK_HOLE {
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fi, err := f.fd.Stat()
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if err != nil {
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return MinusOne, fs.ToErrno(err)
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}
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if newCipherOff == fi.Size() {
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return f.rootNode.contentEnc.CipherSizeToPlainSize(uint64(newCipherOff)), 0
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}
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}
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// syscall.Seek gave us the beginning of the next ext4 data/hole section.
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// The next gocryptfs data/hole block starts at the next block boundary,
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// so we have to round up:
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newBlockNo := f.rootNode.contentEnc.CipherOffToBlockNo(uint64(newCipherOff) + f.rootNode.contentEnc.CipherBS() - 1)
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return f.rootNode.contentEnc.BlockNoToPlainOff(newBlockNo), 0
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}
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@ -2,9 +2,12 @@ package plaintextnames
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import (
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"fmt"
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"math/rand"
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"os"
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"os/exec"
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"syscall"
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"testing"
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"time"
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"github.com/rfjakob/gocryptfs/tests/test_helpers"
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@ -26,38 +29,21 @@ func findHolesPretty(t *testing.T, path string) string {
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return holes.PrettyPrint(segments)
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}
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// TestFileHoleCopy creates a sparse times, copies it a few times, and check if
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// the copies are the same (including the location of holes and data sections).
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//
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// The test runs with -plaintextnames because that makes it easier to manipulate
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// cipherdir directly.
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func TestFileHoleCopy(t *testing.T) {
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n := "TestFileHoleCopy"
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func doTestFileHoleCopy(t *testing.T, name string, writeOffsets []int64) {
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n := "TestFileHoleCopy." + name
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pPath := []string{pDir + "/" + n}
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cPath := []string{cDir + "/" + n}
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f, err := os.Create(pPath[0])
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if err != nil {
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t.Fatal(err)
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}
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// | hole | x | hole | x | hole |
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buf := []byte("x")
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f.WriteAt(buf, 10000)
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f.WriteAt(buf, 30000)
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f.Truncate(50000)
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f.Sync()
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f.Close()
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os.Remove(pPath[0])
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holes.Create(pPath[0])
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// You have to update this value manually when you change the sequence
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// above
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// expected md6
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md5 := test_helpers.Md5fn(pPath[0])
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if md5 != "4e8d0742bccfbcdbf1d71be688e4e81c" {
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t.Fatalf("wrong md5: %s", md5)
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}
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pSegments := []string{findHolesPretty(t, pPath[0])}
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cSegments := []string{findHolesPretty(t, cPath[0])}
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// create 5 more copies
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for i := 1; i < 5; i++ {
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pPath = append(pPath, fmt.Sprintf("%s.%d", pPath[0], i))
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cPath = append(cPath, fmt.Sprintf("%s.%d", cPath[0], i))
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@ -76,21 +62,90 @@ func TestFileHoleCopy(t *testing.T) {
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cSegments = append(cSegments, findHolesPretty(t, cPath[i]))
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}
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// "cp --sparse=auto" checks of the file has fewer blocks on disk than it
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// should have for its size. Only then it will try to create a sparse copy.
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var st syscall.Stat_t
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err := syscall.Stat(pPath[0], &st)
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if err != nil {
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t.Fatal(err)
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}
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// convert 512 byte blocks to 4k blocks
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blocks4k := st.Blocks / 8
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// For more than a few fragments, ext4 allocates one extra block
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blocks4k++
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if blocks4k >= (st.Size+4095)/4096 {
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t.Logf("file will look non-sparse to cp, skipping segment check")
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return
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}
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// Check that size on disk stays the same across copies
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var st0 syscall.Stat_t
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if err := syscall.Stat(pPath[0], &st0); err != nil {
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t.Fatal(err)
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}
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for i := range pSegments {
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t.Logf("pSegments[%d]: %s", i, pSegments[i])
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var st syscall.Stat_t
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if err := syscall.Stat(pPath[i], &st); err != nil {
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t.Fatal(err)
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}
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// Sometimes the size on disk decreases by 4k due to less fragmentation
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if st.Blocks != st0.Blocks && st.Blocks != st0.Blocks-8 {
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t.Errorf("size changed: st0.Blocks=%d st%d.Blocks=%d", st0.Blocks, i, st.Blocks)
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}
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}
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// Check that hole/data segments stays the same across copies
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out := ""
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same := true
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for i := range pSegments {
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out += fmt.Sprintf("pSegments[%d]:\n%s\n", i, pSegments[i])
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if i < len(pSegments)-1 {
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if pSegments[i+1] != pSegments[i] {
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t.Errorf("error: this is different than pSegments[%d]!", i+1)
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same = false
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t.Errorf("error: pSegments[%d] is different than pSegments[%d]!", i, i+1)
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}
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}
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}
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t.Log("------------------------------------")
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out += "------------------------------------\n"
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for i := range cSegments {
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t.Logf("cSegments[%d]: %s", i, cSegments[i])
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out += fmt.Sprintf("cSegments[%d]:\n%s\n", i, cSegments[i])
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if i < len(pSegments)-1 {
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if cSegments[i+1] != cSegments[i] {
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t.Errorf("error: this is different than cSegments[%d]!", i+1)
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same = false
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t.Errorf("error: cSegments[%d] is different than cSegments[%d]!", i, i+1)
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}
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}
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}
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if !same {
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t.Log(out)
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}
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}
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// TestFileHoleCopy creates a sparse times, copies it a few times, and check if
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// the copies are the same (including the location of holes and data sections).
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//
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// The test runs with -plaintextnames because that makes it easier to manipulate
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// cipherdir directly.
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func TestFileHoleCopy(t *testing.T) {
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// | hole | x | hole | x | hole |
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// truncate -s 50000 foo && dd if=/dev/zero of=foo bs=1 seek=10000 count=1 conv=notrunc && dd if=/dev/zero of=foo bs=1 seek=30000 count=1 conv=notrunc
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name := "c0"
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c0 := []int64{10000, 30000}
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if !t.Run("c0", func(t *testing.T) { doTestFileHoleCopy(t, name, c0) }) {
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t.Log("aborting further subtests")
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return
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}
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rand.Seed(time.Now().UnixNano())
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for k := 0; k < 100; k++ {
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c1 := make([]int64, 10)
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for i := range c1 {
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c1[i] = int64(rand.Int31n(60000))
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}
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name := fmt.Sprintf("k%d", k)
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if !t.Run(name, func(t *testing.T) { doTestFileHoleCopy(t, name, c1) }) {
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t.Log("aborting further subtests")
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return
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}
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}
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}
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