[Libguestfs] [PATCH nbdinfo 1/2] common/utils: Add function to convert sizes to human-readable

[Martin Kletzander]

On Sat, Sep 18, 2021 at 03:38:52PM +0100, Richard W.M. Jones wrote:
>For example 1024 is returned as "1K".
>
>This does not attempt to handle decimals or SI units.  If the number
>isn't some multiple of a power of 1024 then it is returned as bytes (a
>flag is available to indicate this).
>
>I looked at both the gnulib and qemu versions of this function.  The
>gnulib version is not under a license which is compatible with libnbd
>and is also really complicated, although it does handle fractions and
>SI units.  The qemu version is essentially just frexp + sprintf and
>doesn't attempt to convert to the human-readable version reversibly.
>---
> .gitignore                     |  1 +
> common/utils/Makefile.am       | 10 +++-
> common/utils/human-size.c      | 54 +++++++++++++++++++++
> common/utils/human-size.h      | 49 +++++++++++++++++++
> common/utils/test-human-size.c | 89 ++++++++++++++++++++++++++++++++++
> 5 files changed, 201 insertions(+), 2 deletions(-)
>
>diff --git a/.gitignore b/.gitignore
>index 2aa1fd99..5fc59677 100644
>--- a/.gitignore
>+++ b/.gitignore
>@@ -31,6 +31,7 @@ Makefile.in
> /bash/nbdcopy
> /bash/nbdfuse
> /bash/nbdinfo
>+/common/utils/test-human-size
> /common/utils/test-vector
> /compile
> /config.cache
>diff --git a/common/utils/Makefile.am b/common/utils/Makefile.am
>index 1ca4a370..b273ada1 100644
>--- a/common/utils/Makefile.am
>+++ b/common/utils/Makefile.am
>@@ -34,6 +34,8 @@ include $(top_srcdir)/common-rules.mk
> noinst_LTLIBRARIES = libutils.la
>
> libutils_la_SOURCES = \
>+	human-size.c \
>+	human-size.h \
> 	vector.c \
> 	vector.h \
> 	version.c \
>@@ -50,8 +52,12 @@ libutils_la_LIBADD = \
>
> # Unit tests.
>
>-TESTS = test-vector
>-check_PROGRAMS = test-vector
>+TESTS = test-human-size test-vector
>+check_PROGRAMS = test-human-size test-vector
>+
>+test_human_size_SOURCES = test-human-size.c human-size.c human-size.h
>+test_human_size_CPPFLAGS = -I$(srcdir)
>+test_human_size_CFLAGS = $(WARNINGS_CFLAGS)
>
> test_vector_SOURCES = test-vector.c vector.c vector.h
> test_vector_CPPFLAGS = -I$(srcdir)
>diff --git a/common/utils/human-size.c b/common/utils/human-size.c
>new file mode 100644
>index 00000000..5cff722b
>--- /dev/null
>+++ b/common/utils/human-size.c
>@@ -0,0 +1,54 @@
>+/* nbd client library in userspace
>+ * Copyright (C) 2020-2021 Red Hat Inc.
>+ *
>+ * This library is free software; you can redistribute it and/or
>+ * modify it under the terms of the GNU Lesser General Public
>+ * License as published by the Free Software Foundation; either
>+ * version 2 of the License, or (at your option) any later version.
>+ *
>+ * This library is distributed in the hope that it will be useful,
>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>+ * Lesser General Public License for more details.
>+ *
>+ * You should have received a copy of the GNU Lesser General Public
>+ * License along with this library; if not, write to the Free Software
>+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>+ */
>+
>+#include <config.h>
>+
>+#include <stdio.h>
>+#include <stdlib.h>
>+#include <stdbool.h>
>+#include <stdint.h>
>+#include <inttypes.h>
>+
>+#include "human-size.h"
>+
>+char *
>+human_size (char *buf, uint64_t bytes, bool *human)
>+{
>+  static const char *ext[] = { "E", "P", "T", "G", "M", "K", "" };
>+  size_t i;
>+
>+  if (buf == NULL) {
>+    buf = malloc (HUMAN_SIZE_LONGEST);
>+    if (buf == NULL)
>+      return NULL;
>+  }
>+
>+  /* Set to false if we're not going to add a human-readable extension. */
>+  if (human)
>+    *human = bytes != 0 && (bytes & 1023) == 0;
>+

It would be more readable (with some de-duplication even) to remove this part ^^ ...

>+  /* Work out which extension to use, if any. */
>+  for (i = 6; i >= 0; --i) {
>+    if (bytes == 0 || (bytes & 1023) != 0)
>+      break;
>+    bytes /= 1024;
>+  }
>+

And just set here:

*human = i == 6;

Even better make it more future-proof and use (sizeof(ext) / sizeof(*ext))
instead of just "6".  Disclaimer: Written by hand, not tested.

>+  snprintf (buf, HUMAN_SIZE_LONGEST-1, "%" PRIu64 "%s", bytes, ext[i]);

The '-1' seems unnecessary here as snprintf() counts the zero terminator as part
the supplied size and will not overrun @size-sized buffers.

But even without the modifications both patches look fine.

Martin
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