move implementation to internal/ directory (#828)

internal/zfs/holds.go

@@ -0,0 +1,134 @@
+package zfs
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"strings"
+	"syscall"
+
+	"github.com/pkg/errors"
+
+	"github.com/zrepl/zrepl/internal/util/envconst"
+	"github.com/zrepl/zrepl/internal/zfs/zfscmd"
+)
+
+// no need for feature tests, holds have been around forever
+
+func validateNotEmpty(field, s string) error {
+	if s == "" {
+		return fmt.Errorf("`%s` must not be empty", field)
+	}
+	return nil
+}
+
+// returned err != nil is guaranteed to represent invalid hold tag
+func ValidHoldTag(tag string) error {
+	maxlen := envconst.Int("ZREPL_ZFS_MAX_HOLD_TAG_LEN", 256-1) // 256 include NULL byte, from module/zfs/dsl_userhold.c
+	if len(tag) > maxlen {
+		return fmt.Errorf("hold tag %q exceeds max length of %d", tag, maxlen)
+	}
+	return nil
+}
+
+// Idemptotent: does not return an error if the tag already exists
+func ZFSHold(ctx context.Context, fs string, v FilesystemVersion, tag string) error {
+	if !v.IsSnapshot() {
+		return errors.Errorf("can only hold snapshots, got %s", v.RelName())
+	}
+
+	if err := validateNotEmpty("tag", tag); err != nil {
+		return err
+	}
+	fullPath := v.FullPath(fs)
+	output, err := zfscmd.CommandContext(ctx, "zfs", "hold", tag, fullPath).CombinedOutput()
+	if err != nil {
+		if bytes.Contains(output, []byte("tag already exists on this dataset")) {
+			goto success
+		}
+		return &ZFSError{output, errors.Wrapf(err, "cannot hold %q", fullPath)}
+	}
+success:
+	return nil
+}
+
+func ZFSHolds(ctx context.Context, fs, snap string) ([]string, error) {
+	if err := validateZFSFilesystem(fs); err != nil {
+		return nil, errors.Wrap(err, "`fs` is not a valid filesystem path")
+	}
+	if snap == "" {
+		return nil, fmt.Errorf("`snap` must not be empty")
+	}
+	dp := fmt.Sprintf("%s@%s", fs, snap)
+	output, err := zfscmd.CommandContext(ctx, "zfs", "holds", "-H", dp).CombinedOutput()
+	if err != nil {
+		return nil, &ZFSError{output, errors.Wrap(err, "zfs holds failed")}
+	}
+	scan := bufio.NewScanner(bytes.NewReader(output))
+	var tags []string
+	for scan.Scan() {
+		// NAME              TAG  TIMESTAMP
+		comps := strings.SplitN(scan.Text(), "\t", 3)
+		if len(comps) != 3 {
+			return nil, fmt.Errorf("zfs holds: unexpected output\n%s", output)
+		}
+		if comps[0] != dp {
+			return nil, fmt.Errorf("zfs holds: unexpected output: expecting %q as first component, got %q\n%s", dp, comps[0], output)
+		}
+		tags = append(tags, comps[1])
+	}
+	return tags, nil
+}
+
+// Idempotent: if the hold doesn't exist, this is not an error
+func ZFSRelease(ctx context.Context, tag string, snaps ...string) error {
+	cumLens := make([]int, len(snaps))
+	for i := 1; i < len(snaps); i++ {
+		cumLens[i] = cumLens[i-1] + len(snaps[i])
+	}
+	maxInvocationLen := 12 * os.Getpagesize()
+	var noSuchTagLines, otherLines []string
+	for i := 0; i < len(snaps); {
+		var j = i
+		for ; j < len(snaps); j++ {
+			if cumLens[j]-cumLens[i] > maxInvocationLen {
+				break
+			}
+		}
+		args := []string{"release", tag}
+		args = append(args, snaps[i:j]...)
+		output, err := zfscmd.CommandContext(ctx, "zfs", args...).CombinedOutput()
+		if pe, ok := err.(*os.PathError); err != nil && ok && pe.Err == syscall.E2BIG {
+			maxInvocationLen = maxInvocationLen / 2
+			continue
+		}
+		// further error handling part of error scraper below
+
+		maxInvocationLen = maxInvocationLen + os.Getpagesize()
+		i = j
+
+		// even if release fails for datasets where there's no hold with the tag
+		// the hold is still released on datasets which have a hold with the tag
+		// FIXME verify this in a platformtest
+		// => screen-scrape
+		scan := bufio.NewScanner(bytes.NewReader(output))
+		for scan.Scan() {
+			line := scan.Text()
+			if strings.Contains(line, "no such tag on this dataset") {
+				noSuchTagLines = append(noSuchTagLines, line)
+			} else {
+				otherLines = append(otherLines, line)
+			}
+		}
+
+	}
+	if debugEnabled {
+		debug("zfs release: no such tag lines=%v otherLines=%v", noSuchTagLines, otherLines)
+	}
+	if len(otherLines) > 0 {
+		return fmt.Errorf("unknown zfs error while releasing hold with tag %q:\n%s", tag, strings.Join(otherLines, "\n"))
+	}
+	return nil
+}