Re: [PATCH 1/7] mkfs: Save raw user input field to the opts struct

Jan Tulak
2017-08-03T13:07:23Z

On 02/08/2017 21:19, Luis R. Rodriguez wrote:
> On Wed, Aug 02, 2017 at 04:30:09PM +0200, Jan Tulak wrote:
>> On 29/07/2017 19:12, Luis R. Rodriguez wrote:
>>> On Fri, Jul 28, 2017 at 04:45:58PM +0200, Jan Tulak wrote:
>>>> On 27/07/2017 18:27, Luis R. Rodriguez wrote:
>>>>> On Thu, Jul 20, 2017 at 11:29:26AM +0200, Jan Tulak wrote:
>>>>>> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
>>>>>> index a69190b9..4b030101 100644
>>>>>> --- a/mkfs/xfs_mkfs.c
>>>>>> +++ b/mkfs/xfs_mkfs.c
>>>>>> @@ -107,6 +107,11 @@ unsigned int sectorsize;
>>>>>> * sets what is used with simple specifying the subopt (-d file).
>>>>>> * A special SUBOPT_NEEDS_VAL can be used to require a user-given
>>>>>> * value in any case.
>>>>>> + *
>>>>>> + * raw_input INTERNAL
>>>>>> + * Filled raw string from the user, so we never lose that information e.g.
>>>>>> + * to print it back in case of an issue.
>>>>>> + *
>>>>>> */
>>>>>> struct opt_params {
>>>>>> const char name;
>>>>>> @@ -122,6 +127,7 @@ struct opt_params {
>>>>>> long long minval;
>>>>>> long long maxval;
>>>>>> long long defaultval;
>>>>>> + const char *raw_input;
>>>>>> } subopt_params[MAX_SUBOPTS];
>>>>>> };
>>>>>> @@ -729,6 +735,18 @@ struct opt_params mopts = {
>>>>>> */
>>>>>> #define WHACK_SIZE (128 * 1024)
>>>>>> +static inline void
>>>>>> +set_conf_raw(struct opt_params *opt, int subopt, const char *value)
>>>>>> +{
>>>>>> + opt->subopt_params[subopt].raw_input = value;
>>>>>> +}
>>>>> There are no bounds check on the array here, I think set_conf_raw()
>>>>> should return int and we would check the return value. It could
>>>>> return -EINVAL if the subopt is invalid for instance.
>>>> Good idea. The only issue is with the return code, that causes some issues
>>>> when we are also returning values - I wanted the values to be turned into
>>>> uint64. But do we need to return an error? I don't see what usecase there
>>>> would be for it, other than detecting a bug. So an assert might be a better
>>>> solution - then it can't happen that a wrong index is used and result not
>>>> tested.
>>> The setting of the value can be done by using an extra argument pointer. Then
>>> if its set it be assigned. Otherwise it would be left alone. The return value
>>> would return 0 on success, otherwise a standard return value indicating the
>>> cause of the error.
>> I strongly prefer to return the value, not an error code. We can do the
>> other way around, put the error code into an argument to get roughly the
>> same result, while constructions like set_conf_raw(FOO, BAR, baz *
>> get_conf_raw(FOO, BAR)) will continue to work without the need for
>> intermediate variables.
>>
>> The *_raw functions are used on few places only, so it would be only a small
>> issue there, but for consistency, (get|set)_conf_val should have the same
>> behavior and an intermediate variable for every use of those would be really
>> annoying. So, how about this?
> It would not be intermediate, the main error variable from the start of
> each function could be used, as is typical in many properly written C
> programs.
I meant value-carrying variables, not the error one:

int temp; // a variable useful only on the next two lines
err = foo(&temp);
bar(temp);

versus:
bar(foo(&err));

The composition of functions would not be usable all the time, it
depends on what would be the return value in case of an error and how
would the outer function deal with it. But when I checked the code, I
think that it could work in a lot of places.
>> static inline void
>> set_conf_raw(struct opt_params *opt, int subopt, const char *value, int
>> *err)
>> {
>> if (subopt < 0 || subopt >= MAX_SUBOPTS) {
>> if (err != NULL) *err = EINVAL;
>> return;
>> }
>> opt->subopt_params[subopt].raw_input = value;
>> }
> If you go with the strdup thing to avoid limiting the context of the use of
> the pointer then you'll still have to return an error or abort, and I think
> returning an error is best.
OK, I'm willing to return errors for the _raw functions. These are used
only on few places, so it is not a big issue. Especially if I add a
wrapper for the get_conf_raw function - right now, these are used only
as fprintf() arguments to print an error. So the wrapper makes it easy
to use in this case (with the old die-on-error behavior), but if you
want to use it for something else, you can use it directly and get an
error as a return code. Does this looks good?

+/*
+ * Return 0 on success, -ENOMEM if it could not allocate enough memory for
+ * the string to be saved into the out pointer.
+ */
+static int
+get_conf_raw(const struct opt_params *opt, const int subopt, char **out)
+{
+ if (subopt < 0 || subopt >= MAX_SUBOPTS) {
+ fprintf(stderr,
+ "This is a bug: get_conf_raw called with invalid
opt/subopt: %c/%d\n",
+ opt->name, subopt);
+ exit(1);
+ }
+ *out = strdup(opt->subopt_params[subopt].raw_input);
+ if (*out == NULL)
+ return -ENOMEM;
+ return 0;
+
+}
+
+/*
+ * Same as get_conf_raw(), except it returns the string through return
+ * and dies on any error.
+ */
+static char *
+get_conf_raw_safe(const struct opt_params *opt, const int subopt)
+{
+ char *str;
+ if (get_conf_raw(opt, subopt, &str) == -ENOMEM) {
+ fprintf(stderr, "Out of memory!");
+ exit(1);
+ }
+ return str;
+}

>
>>> I don't think we need the too small or too big, a simple range issue should
>>> suffice and we have -ERANGE.
>>>
>> At this moment, we are telling if it is too small or too big, but when there
>> is no standard error code for that, ERANGE has to suffice.
> Sure, my point was that we have special values for too big or too small, and
> I consider that hacky, we could just *say* if it was too big or too small
> but just use ERANGE as its standard and non-hacky.
We don't have special values, we just print it out and die. But yes, if
we will pass the information anywhere, then it is better to use ERANGE
rather than some custom error number.

Jan