move implementation to internal/ directory (#828)

internal/zfs/zfs_pipe_linux.go

@@ -0,0 +1,42 @@
+package zfs
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/zrepl/zrepl/internal/util/envconst"
+)
+
+func getPipeCapacityHint(envvar string) int {
+	var capacity int64 = 1 << 25
+
+	// Work around a race condition in Linux >= 5.8 related to pipe resizing.
+	// https://github.com/zrepl/zrepl/issues/424#issuecomment-800370928
+	// https://bugzilla.kernel.org/show_bug.cgi?id=212295
+	if _, err := os.Stat("/proc/sys/fs/pipe-max-size"); err == nil {
+		if dat, err := os.ReadFile("/proc/sys/fs/pipe-max-size"); err == nil {
+			if capacity, err = strconv.ParseInt(strings.TrimSpace(string(dat)), 10, 64); err != nil {
+				capacity = 1 << 25
+			}
+		}
+	}
+
+	return int(envconst.Int64(envvar, capacity))
+}
+
+func trySetPipeCapacity(p *os.File, capacity int) {
+	res, err := unix.FcntlInt(p.Fd(), unix.F_SETPIPE_SZ, capacity)
+	if err != nil {
+		err = fmt.Errorf("cannot set pipe capacity to %v", capacity)
+	} else if res == -1 {
+		err = errors.New("cannot set pipe capacity: fcntl returned -1")
+	}
+	if debugEnabled && err != nil {
+		debug("trySetPipeCapacity error: %s\n", err)
+	}
+}