Re: [PATCH v2 08/17] virstring: Introduce virStringIsNull()

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(a)redhat.com&gt; > --- > 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);