Re: [Libguestfs] [PATCH libnbd v3 2/3] copy: Use preferred block size for copying
On 06/30/22 17:47, Richard W.M. Jones wrote:
On Thu, Jun 30, 2022 at 05:38:14PM +0200, Laszlo Ersek wrote:
> On 06/29/22 15:36, Richard W.M. Jones wrote:
>> + * The invariant for '*i' is always an extent which starts before or
>> + * equal to the current offset.
>> + */
>> +static bool
>> +only_zeroes (const extent_list exts, size_t *i,
>
> (5) I think it's a bit wasteful (or at least strange) to pass in the
> entire vector structure; we certainly don't need the "cap" field.
Other
> functions in libnbd seem to take pointers to vectors (which is what I'd
> expect).
Note it's only passing in 3 fields (24 bytes), not the entire array
(and I guess it should inline the whole function). Does that change
things?
It's not wrong by any means, just unusual :) Whole-structure passing and
returning is really rare in my understanding, div() is one standard
function that does it. I don't insist :)
>> @@ -177,7 +229,10 @@ worker_thread (void *wp)
>> extent_list exts = empty_vector;
>>
>> while (get_next_offset (&offset, &count)) {
>> + struct command *command;
>> size_t i;
>> + bool is_zeroing = false;
>> + uint64_t zeroing_start = 0;
>
> (14) I think we should not initialize "zeroing_start". It suggests that
> the initializer value is meaningful, but it is not.
GCC warns if you don't initialize it! It doesn't understand that
is_zeroing is related to the validity of zeroing_start.
We use "#pragma GCC diagnostic" elsewhere in libnbd (in particular in
"copy/progress.c"), can we use it here too? (Just for this one variable?)
If not, I'd suggest appending a small comment:
uint64_t zeroing_start = 0; /* shut up invalid GCC warning */
Thanks for the other suggestions, I'll rework things.
Rich.
Thanks!
Laszlo