Re: [PATCH 2/9] virstring: Introduce virStringIsNull()

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(a)redhat.com&gt; --- 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. */

+ 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