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hallynhallyn
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Merge pull request #1560 from stgraber/main
Expand block reset logic
2 parents fc4d0ca + d4acafd commit d5b4251

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3 files changed

+234
-47
lines changed

3 files changed

+234
-47
lines changed

‎internal/linux/discard.go

+222
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,222 @@
1+
package linux
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import (
4+
"fmt"
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"io"
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"os"
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"github.com/lxc/incus/v6/shared/subprocess"
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)
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// ClearBlock fully resets a block device or disk file using the most efficient mechanism available.
12+
// For files, it will truncate them down to zero and back to their original size.
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// For blocks, it will attempt a variety of discard options, validating the result with marker files and eventually fallback to full zero-ing.
14+
func ClearBlock(blockPath string) error {
15+
// Open the block device for checking.
16+
fd, err := os.OpenFile(blockPath, os.O_RDWR, 0644)
17+
if err != nil {
18+
if os.IsNotExist(err) {
19+
// If the file is missing, there is nothing to clear.
20+
return nil
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}
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return err
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}
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defer fd.Close()
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// Get the size of the file/block.
29+
size, err := fd.Seek(0, io.SeekEnd)
30+
if err != nil {
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return err
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}
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// Get all the stat data.
35+
st, err := fd.Stat()
36+
if err != nil {
37+
return err
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}
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if !IsBlockdev(st.Mode()) {
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// For files, truncate them.
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err := fd.Truncate(0)
43+
if err != nil {
44+
return err
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}
46+
47+
err = fd.Truncate(size)
48+
if err != nil {
49+
return err
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}
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return nil
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}
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// Blocks are trickier to reset with options varying based on disk features.
56+
// We use a set of 3 markers to validate whether it was reset.
57+
marker := []byte("INCUS")
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markerOffsetStart := int64(0)
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markerOffsetMiddle := size / 2
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markerOffsetEnd := size - 10
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writeMarkers := func(fd *os.File) error {
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for _, offset := range []int64{markerOffsetStart, markerOffsetMiddle, markerOffsetEnd} {
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// Write the marker at the set offset.
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n, err := fd.WriteAt(marker, offset)
66+
if err != nil {
67+
return err
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}
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70+
if n != len(marker) {
71+
return fmt.Errorf("Only managed to write %d bytes out of %d of the %d offset marker", n, len(marker), offset)
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}
73+
}
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return nil
76+
}
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checkMarkers := func(fd *os.File) (int, error) {
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found := 0
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for _, offset := range []int64{markerOffsetStart, markerOffsetMiddle, markerOffsetEnd} {
82+
fmt.Printf("offset=%d\n", offset)
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buf := make([]byte, 5)
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// Read the marker from the offset.
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n, err := fd.ReadAt(buf, offset)
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if err != nil {
88+
return found, err
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}
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if n != len(marker) {
92+
return found, fmt.Errorf("Only managed to read %d bytes out of %d of the %d offset marker", n, len(marker), offset)
93+
}
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// Check if we found it.
96+
if string(buf) == string(marker) {
97+
found++
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}
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}
100+
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return found, nil
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}
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// Write and check an initial set of markers.
105+
err = writeMarkers(fd)
106+
if err != nil {
107+
return err
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}
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found, err := checkMarkers(fd)
111+
if err != nil {
112+
return err
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}
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if found != 3 {
116+
return fmt.Errorf("Some of our initial markers weren't written properly")
117+
}
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// Start clearing the block.
120+
_ = fd.Close()
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122+
// Attempt a secure discard run.
123+
_, err = subprocess.RunCommand("blkdiscard", "-f", "-s", blockPath)
124+
if err == nil {
125+
// Check if the markers are gone.
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fd, err := os.Open(blockPath)
127+
if err != nil {
128+
return err
129+
}
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131+
defer fd.Close()
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found, err = checkMarkers(fd)
134+
if err != nil {
135+
return err
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}
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if found == 0 {
139+
// All markers are gone, secure discard succeeded.
140+
return nil
141+
}
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// Some markers were found, go to the next clearing option.
144+
_ = fd.Close()
145+
}
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147+
// Attempt a regular discard run.
148+
_, err = subprocess.RunCommand("blkdiscard", "-f", blockPath)
149+
if err == nil {
150+
// Check if the markers are gone.
151+
fd, err := os.Open(blockPath)
152+
if err != nil {
153+
return err
154+
}
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156+
defer fd.Close()
157+
158+
found, err = checkMarkers(fd)
159+
if err != nil {
160+
return err
161+
}
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163+
if found == 0 {
164+
// All markers are gone, regular discard succeeded.
165+
return nil
166+
}
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168+
// Some markers were found, go to the next clearing option.
169+
_ = fd.Close()
170+
}
171+
172+
// Attempt device zero-ing.
173+
_, err = subprocess.RunCommand("blkdiscard", "-f", "-z", blockPath)
174+
if err == nil {
175+
// Check if the markers are gone.
176+
fd, err := os.Open(blockPath)
177+
if err != nil {
178+
return err
179+
}
180+
181+
defer fd.Close()
182+
183+
found, err = checkMarkers(fd)
184+
if err != nil {
185+
return err
186+
}
187+
188+
if found == 0 {
189+
// All markers are gone, device zero-ing succeeded.
190+
return nil
191+
}
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193+
// Some markers were found, go to the next clearing option.
194+
_ = fd.Close()
195+
}
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197+
// All fast discard attempts have failed, proceed with manual zero-ing.
198+
zero, err := os.Open("/dev/zero")
199+
if err != nil {
200+
return err
201+
}
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203+
defer zero.Close()
204+
205+
fd, err = os.OpenFile(blockPath, os.O_WRONLY, 0644)
206+
if err != nil {
207+
return err
208+
}
209+
210+
defer fd.Close()
211+
212+
n, err := io.CopyN(fd, zero, size)
213+
if err != nil {
214+
return err
215+
}
216+
217+
if n != size {
218+
return fmt.Errorf("Only managed to reset %d bytes out of %d", n, size)
219+
}
220+
221+
return nil
222+
}

‎internal/server/storage/drivers/generic_vfs.go

+12-12
Original file line numberDiff line numberDiff line change
@@ -325,19 +325,19 @@ func genericVFSCreateVolumeFromMigration(d Driver, initVolume func(vol Volume) (
325325
wrapper = localMigration.ProgressTracker(op, "block_progress", volName)
326326
}
327327

328+
// Reset the disk.
329+
err := linux.ClearBlock(path)
330+
if err != nil {
331+
return err
332+
}
333+
328334
to, err := os.OpenFile(path, os.O_WRONLY|os.O_TRUNC, 0)
329335
if err != nil {
330336
return fmt.Errorf("Error opening file for writing %q: %w", path, err)
331337
}
332338

333339
defer func() { _ = to.Close() }()
334340

335-
// Reset the disk.
336-
err = clearDiskData(path, to)
337-
if err != nil {
338-
return err
339-
}
340-
341341
// Setup progress tracker.
342342
fromPipe := io.ReadCloser(conn)
343343
if wrapper != nil {
@@ -769,6 +769,12 @@ func genericVFSBackupUnpack(d Driver, sysOS *sys.OS, vol Volume, snapshots []str
769769
if hdr.Name == srcFile {
770770
var allowUnsafeResize bool
771771

772+
// Reset the disk.
773+
err = linux.ClearBlock(targetPath)
774+
if err != nil {
775+
return err
776+
}
777+
772778
// Open block file (use O_CREATE to support drivers that use image files).
773779
to, err := os.OpenFile(targetPath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
774780
if err != nil {
@@ -793,12 +799,6 @@ func genericVFSBackupUnpack(d Driver, sysOS *sys.OS, vol Volume, snapshots []str
793799
logMsg = "Unpacking custom block volume"
794800
}
795801

796-
// Reset the disk.
797-
err = clearDiskData(targetPath, to)
798-
if err != nil {
799-
return err
800-
}
801-
802802
// Copy the data.
803803
d.Logger().Debug(logMsg, logger.Ctx{"source": srcFile, "target": targetPath})
804804
_, err = io.Copy(NewSparseFileWrapper(to), tr)

‎internal/server/storage/drivers/utils.go

-35
Original file line numberDiff line numberDiff line change
@@ -957,38 +957,3 @@ func roundAbove(above, val int64) int64 {
957957

958958
return rounded
959959
}
960-
961-
// clearDiskData resets a disk file or device to a zero value.
962-
func clearDiskData(diskPath string, disk *os.File) error {
963-
st, err := disk.Stat()
964-
if err != nil {
965-
return err
966-
}
967-
968-
if linux.IsBlockdev(st.Mode()) {
969-
// If dealing with a block device, attempt to discard its current content.
970-
// This saves space and avoids issues with leaving zero blocks to their original value.
971-
_, err = subprocess.RunCommand("blkdiscard", "-f", diskPath)
972-
if err != nil {
973-
logger.Debugf("Unable to clear disk data on %q: %v", diskPath, err)
974-
}
975-
} else {
976-
// Otherwise truncate the file.
977-
err = disk.Truncate(0)
978-
if err != nil {
979-
return err
980-
}
981-
982-
err = disk.Truncate(st.Size())
983-
if err != nil {
984-
return err
985-
}
986-
987-
_, err = disk.Seek(0, 0)
988-
if err != nil {
989-
return err
990-
}
991-
}
992-
993-
return nil
994-
}

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