[PATCH 3/3] utils: Deprecate inexact fractional suffix sizes

[Eric Blake <eblake@redhat.com>]

The value '1.1k' is inexact; 1126.4 bytes is not possible, so we
happen to truncate it to 1126.  Our use of fractional sizes is
intended for convenience, but when a user specifies a fraction that is
not a clean translation to binary, truncating/rounding behind their
backs can cause confusion.  Better is to deprecate inexact values,
which still leaves '1.5k' as valid, but alerts the user to spell out
their values as a precise byte number in cases where they are
currently being rounded.

Note that values like '0.1G' in the testsuite need adjustment as a
result.

Sadly, since qemu_strtosz() does not have an Err** parameter, we
pollute to stderr.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 tests/test-cutils.c    | 4 ++--
 tests/test-keyval.c    | 4 ++--
 tests/test-qemu-opts.c | 4 ++--
 util/cutils.c          | 4 ++++
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/tests/test-cutils.c b/tests/test-cutils.c
index 0c2c89d6f113..ad51fb1baa51 100644
--- a/tests/test-cutils.c
+++ b/tests/test-cutils.c
@@ -2095,14 +2095,14 @@ static void test_qemu_strtosz_units(void)

 static void test_qemu_strtosz_float(void)
 {
-    const char *str = "12.345M";
+    const char *str = "12.125M";
     int err;
     const char *endptr;
     uint64_t res = 0xbaadf00d;

     err = qemu_strtosz(str, &endptr, &res);
     g_assert_cmpint(err, ==, 0);
-    g_assert_cmpint(res, ==, 12.345 * MiB);
+    g_assert_cmpint(res, ==, 12.125 * MiB);
     g_assert(endptr == str + 7);
 }

diff --git a/tests/test-keyval.c b/tests/test-keyval.c
index 13be763650b2..c951ac54cd23 100644
--- a/tests/test-keyval.c
+++ b/tests/test-keyval.c
@@ -522,7 +522,7 @@ static void test_keyval_visit_size(void)
     visit_free(v);

     /* Suffixes */
-    qdict = keyval_parse("sz1=8b,sz2=1.5k,sz3=2M,sz4=0.1G,sz5=16777215T",
+    qdict = keyval_parse("sz1=8b,sz2=1.5k,sz3=2M,sz4=0.125G,sz5=16777215T",
                          NULL, NULL, &error_abort);
     v = qobject_input_visitor_new_keyval(QOBJECT(qdict));
     qobject_unref(qdict);
@@ -534,7 +534,7 @@ static void test_keyval_visit_size(void)
     visit_type_size(v, "sz3", &sz, &error_abort);
     g_assert_cmphex(sz, ==, 2 * MiB);
     visit_type_size(v, "sz4", &sz, &error_abort);
-    g_assert_cmphex(sz, ==, GiB / 10);
+    g_assert_cmphex(sz, ==, GiB / 8);
     visit_type_size(v, "sz5", &sz, &error_abort);
     g_assert_cmphex(sz, ==, 16777215ULL * TiB);
     visit_check_struct(v, &error_abort);
diff --git a/tests/test-qemu-opts.c b/tests/test-qemu-opts.c
index f79b698e6715..6a1ea1d01c4f 100644
--- a/tests/test-qemu-opts.c
+++ b/tests/test-qemu-opts.c
@@ -717,10 +717,10 @@ static void test_opts_parse_size(void)
     g_assert_cmphex(qemu_opt_get_size(opts, "size1", 0), ==, 8);
     g_assert_cmphex(qemu_opt_get_size(opts, "size2", 0), ==, 1536);
     g_assert_cmphex(qemu_opt_get_size(opts, "size3", 0), ==, 2 * MiB);
-    opts = qemu_opts_parse(&opts_list_02, "size1=0.1G,size2=16777215T",
+    opts = qemu_opts_parse(&opts_list_02, "size1=0.125G,size2=16777215T",
                            false, &error_abort);
     g_assert_cmpuint(opts_count(opts), ==, 2);
-    g_assert_cmphex(qemu_opt_get_size(opts, "size1", 0), ==, GiB / 10);
+    g_assert_cmphex(qemu_opt_get_size(opts, "size1", 0), ==, GiB / 8);
     g_assert_cmphex(qemu_opt_get_size(opts, "size2", 0), ==, 16777215ULL * TiB);

     /* Beyond limit with suffix */
diff --git a/util/cutils.c b/util/cutils.c
index 75190565cbb5..5ec6101ae778 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -327,6 +327,10 @@ static int do_strtosz(const char *nptr, const char **end,
         retval = -ERANGE;
         goto out;
     }
+    if (mul_required && fraction * mul != (uint64_t) (fraction * mul)) {
+        fprintf(stderr, "Using a fractional size that is not an exact byte "
+                "multiple is deprecated: %s\n", nptr);
+    }
     *result = val * mul + (uint64_t) (fraction * mul);
     retval = 0;

-- 
2.30.0