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.
Since qemu_strtosz() does not have an Err** parameter, and plumbing
that in would be a much larger task, we instead go with just directly
emitting the deprecation warning to stderr.
Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
---
I'm not a fan of this patch, but am proposing it for discussion purposes.
---
docs/system/deprecated.rst | 9 +++++++++
tests/test-cutils.c | 6 +++---
tests/test-keyval.c | 4 ++--
tests/test-qemu-opts.c | 4 ++--
util/cutils.c | 9 +++++++--
5 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 113c2e933f1b..2c9cb849eec5 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -154,6 +154,15 @@ Input parameters that take a size value should only use a size suffix
the value is hexadecimal. That is, '0x20M' is deprecated, and should
be written either as '32M' or as '0x2000000'.
+inexact sizes via scaled fractions (since 6.0)
+''''''''''''''''''''''''''''''''''''''''''''''
+
+Input parameters that take a size value should only use a fractional
+size (such as '1.5M') that will result in an exact byte value. The
+use of inexact values (such as '1.1M') that require truncation or
+rounding is deprecated, and you should instead consider writing your
+unusual size in bytes (here, '1153433' or '1153434' as desired).
+
QEMU Machine Protocol (QMP) commands
------------------------------------
diff --git a/tests/test-cutils.c b/tests/test-cutils.c
index bad3a6099389..c6c33866277b 100644
--- a/tests/test-cutils.c
+++ b/tests/test-cutils.c
@@ -2124,11 +2124,11 @@ static void test_qemu_strtosz_float(void)
g_assert_cmpint(res, ==, 1024);
g_assert(endptr == str + 3);
- /* For convenience, we permit values that are not byte-exact */
- str = "12.345M";
+ /* Fractional values should still be byte-exact */
+ str = "12.125M";
err = qemu_strtosz(str, &endptr, &res);
g_assert_cmpint(err, ==, 0);
- g_assert_cmpint(res, ==, (uint64_t) (12.345 * MiB));
+ g_assert_cmpint(res, ==, (uint64_t) (12.125 * MiB));
g_assert(endptr == str + 7);
}
diff --git a/tests/test-keyval.c b/tests/test-keyval.c
index e20c07cf3ea5..7a45c22942e6 100644
--- a/tests/test-keyval.c
+++ b/tests/test-keyval.c
@@ -525,7 +525,7 @@ 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);
@@ -537,7 +537,7 @@ 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 6568e31a7229..549e994938fe 100644
--- a/tests/test-qemu-opts.c
+++ b/tests/test-qemu-opts.c
@@ -720,10 +720,10 @@ 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 6a8a175e0d71..1154b9de131a 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -246,12 +246,13 @@ static int64_t suffix_mul(char suffix, int64_t unit)
* The size parsing supports the following syntaxes
* - 12345 - decimal, scale determined by @default_suffix and @unit
* - 12345{bBkKmMgGtTpPeE} - decimal, scale determined by suffix and @unit
- * - 12345.678{kKmMgGtTpPeE} - decimal, scale determined by suffix, and
- * fractional portion is truncated to byte
+ * - 12345.678{kKmMgGtTpPeE} - decimal, scale determined by suffix, if
+ * fractional portion is exact
* - 0x7fEE - hexadecimal, unit determined by @default_suffix
*
* The following cause a deprecation warning, and may be removed in the future
* - 0xabc{kKmMgGtTpP} - hex with scaling suffix
+ * - 12345.678{kKmMgGtTpPeE} - decimal with inexact fraction that caused truncation
*
* The following are intentionally not supported
* - octal, such as 08
@@ -342,6 +343,10 @@ static int do_strtosz(const char *nptr, const char **end,
retval = -ERANGE;
goto out;
}
+ if (mul_required && fraction * mul != (uint64_t) (fraction * mul)) {
+ warn_report("Using a fractional size that is not an exact byte "
+ "multiple is deprecated: %s", nptr);
+ }
*result = val * mul + (uint64_t) (fraction * mul);
retval = 0;
--
2.30.1
