[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>
---
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