Libguestfs - Oct 2023 - [libnbd PATCH 1/2] utils: Slightly simplify human_size()

Based on Laszlo's approval of my idea here:
https://listman.redhat.com/archives/libguestfs/2023-September/032661.html

but as I would like to resync human-size.h back to nbdkit, I'm
reluctant to apply patch 1 this until I get Rich's consent to
relicensing (this email serves as my consent for my contribution here):
https://listman.redhat.com/archives/libguestfs/2023-October/032755.html

Eric Blake (2):
  utils: Slightly simplify human_size()
  info: Show human sizes for block_size values

 common/include/human-size.h | 14 ++++++--------
 info/show.c                 | 26 +++++++++++++++++++-------
 2 files changed, 25 insertions(+), 15 deletions(-)

-- 
2.41.0

Use an array of characters instead of strings for less .data storage.
Merge the loop conditional for fewer lines of code.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 common/include/human-size.h | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/common/include/human-size.h b/common/include/human-size.h
index 47729c3c..8b1e0132 100644
--- a/common/include/human-size.h
+++ b/common/include/human-size.h
@@ -159,7 +159,7 @@ human_size_parse (const char *str,
 static inline char *
 human_size (char *buf, uint64_t bytes, bool *human)
 {
-  static const char ext[][2] = { "E", "P", "T",
"G", "M", "K", "" };
+  static const char ext[] = "EPTGMK";
   size_t i;

   if (buf == NULL) {
@@ -170,18 +170,16 @@ human_size (char *buf, uint64_t bytes, bool *human)

   /* Work out which extension to use, if any. */
   i = 6;
-  if (bytes != 0) {
-    while ((bytes & 1023) == 0) {
-      bytes >>= 10;
-      i--;
-    }
+  while (bytes && (bytes & 1023) == 0) {
+    bytes >>= 10;
+    i--;
   }

   /* Set the flag to true if we're going to add a human-readable extension.
*/
   if (human)
-    *human = ext[i][0] != '\0';
+    *human = ext[i] != '\0';

-  snprintf (buf, HUMAN_SIZE_LONGEST, "%" PRIu64 "%s",
bytes, ext[i]);
+  snprintf (buf, HUMAN_SIZE_LONGEST, "%" PRIu64 "%.1s",
bytes, &ext[i]);
   return buf;
 }

-- 
2.41.0

Adding a human-readable size for block constraints is useful.  For:

$ ./run nbdinfo -- [ nbdkit memory \
   --filter=blocksize-policy blocksize-preferred=32k 1M ] | grep pref

this changes pre-patch:
	block_size_preferred: 32768
to post-patch:
	block_size_preferred: 32768 (32K)

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 info/show.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/info/show.c b/info/show.c
index 6aeffb54..ac483f34 100644
--- a/info/show.c
+++ b/info/show.c
@@ -35,6 +35,7 @@
 #include "nbdinfo.h"

 static void show_boolean (const char *name, bool cond);
+static void show_size (const char *name, int64_t size);
 static int collect_context (void *opaque, const char *name);
 static char *get_content (struct nbd_handle *, int64_t size);

@@ -181,13 +182,9 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
       show_boolean ("can_trim", can_trim);
     if (can_zero >= 0)
       show_boolean ("can_zero", can_zero);
-    if (block_minimum > 0)
-      fprintf (fp, "\t%s: %" PRId64 "\n",
"block_size_minimum", block_minimum);
-    if (block_preferred > 0)
-      fprintf (fp, "\t%s: %" PRId64 "\n",
"block_size_preferred",
-               block_preferred);
-    if (block_maximum > 0)
-      fprintf (fp, "\t%s: %" PRId64 "\n",
"block_size_maximum", block_maximum);
+    show_size ("block_size_minimum", block_minimum);
+    show_size ("block_size_preferred", block_preferred);
+    show_size ("block_size_maximum", block_maximum);
   }
   else {
     if (first)
@@ -304,6 +301,21 @@ show_boolean (const char *name, bool cond)
   ansi_restore (fp);
 }

+/* Used for displaying sizes in non-JSON output. */
+void show_size (const char *name, int64_t size)
+{
+  char size_str[HUMAN_SIZE_LONGEST];
+  bool human_size_flag = false;
+
+  if (size > 0) {
+    human_size (size_str, size, &human_size_flag);
+    if (human_size_flag)
+      fprintf (fp, "\t%s: %" PRId64 " (%s)\n", name, size,
size_str);
+    else
+      fprintf (fp, "\t%s: %" PRId64 "\n", name, size);
+  }
+}
+
 static int
 collect_context (void *opaque, const char *name)
 {
-- 
2.41.0