Thales Maciel
ed4117d926
mkfs.ext4's positional fs-size is documented in 1 KiB units (not the filesystem's 4 KiB block size), so passing sizeBytes/4096 made filesystems 1/4 the intended size. A 4 GiB request became a 1 GiB ext4 in a 4 GiB file, packed to 0 free blocks — VM create then failed with 'Could not allocate block' when patchRootOverlay tried to write guest config. The file is truncated to the target size before mkfs runs; without the positional arg, mkfs uses the whole device. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
73 lines
2.1 KiB
Go
73 lines
2.1 KiB
Go
package imagepull
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import (
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"context"
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"errors"
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"fmt"
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"os"
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"banger/internal/system"
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)
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// MinExt4Size is the smallest ext4 image we'll create. mkfs.ext4 needs a
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// few megabytes for its bookkeeping; for a real rootfs the staging tree
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// will dominate anyway.
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const MinExt4Size int64 = 1 << 20 * 64 // 64 MiB
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// BuildExt4 creates outFile as a sparse ext4 image of sizeBytes and
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// populates it from srcDir using `mkfs.ext4 -F -d`. No mount, no sudo.
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//
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// sizeBytes must be at least MinExt4Size. Callers are expected to size
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// the file with headroom over the staged tree (the daemon orchestrator
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// does this; this function only enforces a sanity floor).
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//
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// The resulting image's file ownership reflects srcDir's on-disk
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// ownership — see the package doc for the implications.
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func BuildExt4(ctx context.Context, runner system.CommandRunner, srcDir, outFile string, sizeBytes int64) error {
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if sizeBytes < MinExt4Size {
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return fmt.Errorf("ext4 size %d below minimum %d", sizeBytes, MinExt4Size)
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}
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info, err := os.Stat(srcDir)
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if err != nil {
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return fmt.Errorf("stat source: %w", err)
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}
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if !info.IsDir() {
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return fmt.Errorf("%s is not a directory", srcDir)
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}
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if err := os.Remove(outFile); err != nil && !errors.Is(err, os.ErrNotExist) {
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return err
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}
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f, err := os.OpenFile(outFile, os.O_CREATE|os.O_WRONLY|os.O_EXCL, 0o644)
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if err != nil {
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return err
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}
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if err := f.Truncate(sizeBytes); err != nil {
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_ = f.Close()
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_ = os.Remove(outFile)
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return err
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}
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if err := f.Close(); err != nil {
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_ = os.Remove(outFile)
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return err
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}
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// mkfs.ext4's positional `fs-size` is documented in 1 KiB units
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// (NOT the filesystem's 4 KiB block size), so dividing by 4096
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// produces a filesystem 1/4 the intended size. Omit the positional
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// entirely — the file was truncated to sizeBytes above, and mkfs
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// with no fs-size arg uses the whole device.
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out, runErr := runner.Run(ctx, "mkfs.ext4",
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"-F",
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"-q",
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"-d", srcDir,
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"-L", "banger-rootfs",
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"-E", "root_owner=0:0",
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outFile,
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)
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if runErr != nil {
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_ = os.Remove(outFile)
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return fmt.Errorf("mkfs.ext4 -d: %w: %s", runErr, string(out))
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}
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return nil
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}
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