On Fri, Jul 03, 2020 at 12:28:43PM +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.
>
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
> src/libvirt_private.syms | 1 +
> src/util/virstring.c | 40 ++++++++++++++++++++++++++++++++++++++++
> src/util/virstring.h | 2 ++
> 3 files changed, 43 insertions(+)
>
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index ae0e253ab9..1d80aeb833 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -3197,6 +3197,7 @@ virStringHasChars;
> virStringHasControlChars;
> virStringHasSuffix;
> virStringIsEmpty;
> +virStringIsNull;
> virStringIsPrintable;
> virStringListAdd;
> virStringListAutoFree;
> diff --git a/src/util/virstring.c b/src/util/virstring.c
> index e9e792f3bf..7f6871d5ab 100644
> --- a/src/util/virstring.c
> +++ b/src/util/virstring.c
> @@ -1404,3 +1404,43 @@ int virStringParseYesNo(const char *str, bool *result)
>
> return 0;
> }
> +
> +
> +/**
> + * virStringIsNull:
> + * @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 or not.
> + *
> + * 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. memcmp() below uses block of sizeof(long)
> + * size (in most cases on 64bits is 8 bytes), doing twice the size just to
> + * be safe. */
On 32-bit this is only going to do 8 bytes though. I'm not sure
why we need "2 * sizeof(long)" instead of "16". Unless we really
do want this to have different behaviour based on sizeof(long),
in which case the comment could be clearer
> + for (;;) {
> + if (*p)
> + return false;
> +
> + p++;
> + len--;
> +
> + if (!len)
> + return true;
> +
> + if ((len & (2 * sizeof(long))) == 0)
> + break;
> + }
> +
> + /* Now we know first 16 bytes are NUL, memcmp with self. */
> + return memcmp(buf, p, len) == 0;
> +}
> diff --git a/src/util/virstring.h b/src/util/virstring.h
> index 360c68395c..d0e54358ac 100644
> --- a/src/util/virstring.h
> +++ b/src/util/virstring.h
> @@ -185,6 +185,8 @@ int virStringParsePort(const char *str,
> int virStringParseYesNo(const char *str,
> bool *result)
> G_GNUC_WARN_UNUSED_RESULT;
> +bool virStringIsNull(const char *buf, size_t len);
> +
> /**
> * VIR_AUTOSTRINGLIST:
> *
> --
> 2.26.2
>
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
