On Tue, Jul 07, 2020 at 21:46:26 +0200, Michal Privoznik wrote:
> This function will be used to detect zero buffers (which are
> going to be interpreted as hole in virStream later).
>
> I shamelessly took inspiration from coreutils.
Coreutils is proudly GPLv3 ...
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
> src/libvirt_private.syms | 1 +
> src/util/virstring.c | 38 ++++++++++++++++++++++++++++++++
> src/util/virstring.h | 2 ++
> tests/virstringtest.c | 47 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 88 insertions(+)
[...]
> diff --git a/src/util/virstring.c b/src/util/virstring.c
> index e9e792f3bf..c26bc770d4 100644
> --- a/src/util/virstring.c
> +++ b/src/util/virstring.c
> @@ -1404,3 +1404,41 @@ int virStringParseYesNo(const char *str, bool *result)
>
> return 0;
> }
> +
> +
> +/**
> + * virStringIsNull:
IsNull might indicate that this does a check if the pointer is NULL. You
are checking for NUL bytes.
> + * @buf: buffer to check
> + * @len: the length of the buffer
> + *
> + * For given buffer @buf and its size @len determine whether
> + * it contains only zero bytes (NUL) or not.
Given the semantics of C strings being terminated by the NUL byte I
don't think this function qualifies as a string helper and thus should
probably reside somewhere outside of virstring.h
> + *
> + * Returns: true if buffer is full of zero bytes,
> + * false otherwise.
> + */
> +bool virStringIsNull(const char *buf, size_t len)
> +{
> + const char *p = buf;
> +
> + if (!len)
> + return true;
> +
> + /* Check up to 16 first bytes. */
> + for (;;) {
> + if (*p)
> + return false;
> +
> + p++;
> + len--;
> +
> + if (!len)
> + return true;
> +
> + if ((len & 0xf) == 0)
> + break;
> + }
Do we really need to do this optimization? We could arguably simplify
this to:
if (*buf != '\0')
return false;
return memcmp(buf, buf + 1, len - 1);
You can then use the saved lines to explain that comparing a piece of
memory with itself shifted by any position just ensures that there are
repeating sequences of itself in the remainder and by shifting it by 1
it means that it checks that the strings are just the same byte. The
check above then ensuers that the one byte is NUL.
