[Libguestfs] [PATCH v2 nbdkit 4/6] common: Add a directory for common code shared by plugins and filters.

Richard W.M. Jones rjones at redhat.com
Wed Aug 1 11:10:27 UTC 2018 

Currently this adds two useful header files containing functions which
will be consumed by filters in later commits.
---
 Makefile.am                 |  5 +++-
 common/include/Makefile.am  | 39 ++++++++++++++++++++++++
 common/include/ispowerof2.h | 50 +++++++++++++++++++++++++++++++
 common/include/iszero.h     | 60 +++++++++++++++++++++++++++++++++++++
 configure.ac                |  1 +
 5 files changed, 154 insertions(+), 1 deletion(-)

diff --git a/Makefile.am b/Makefile.am
index 6a3a377..09dbdb9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -53,7 +53,10 @@ SUBDIRS = \
 	src
 
 if HAVE_PLUGINS
-SUBDIRS += plugins filters
+SUBDIRS += \
+	common/include \
+	plugins \
+	filters
 endif
 
 SUBDIRS += tests
diff --git a/common/include/Makefile.am b/common/include/Makefile.am
new file mode 100644
index 0000000..4ce1723
--- /dev/null
+++ b/common/include/Makefile.am
@@ -0,0 +1,39 @@
+# nbdkit
+# Copyright (C) 2018 Red Hat Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+include $(top_srcdir)/common-rules.mk
+
+# These headers contain only common code shared by plugins and
+# filters.  They are not installed.
+EXTRA_DIST = \
+	ispowerof2.h \
+	iszero.h
diff --git a/common/include/ispowerof2.h b/common/include/ispowerof2.h
new file mode 100644
index 0000000..41844b3
--- /dev/null
+++ b/common/include/ispowerof2.h
@@ -0,0 +1,50 @@
+/* nbdkit
+ * Copyright (C) 2018 Red Hat Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Red Hat nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef NBDKIT_ISPOWEROF2_H
+#define NBDKIT_ISPOWEROF2_H
+
+#include <stdbool.h>
+
+/* Returns true if v is a power of 2.
+ *
+ * Uses the algorithm described at
+ * http://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
+ */
+static inline bool
+is_power_of_2 (unsigned long v)
+{
+  return v && ((v & (v - 1)) == 0);
+}
+
+#endif /* NBDKIT_ISPOWEROF2_H */
diff --git a/common/include/iszero.h b/common/include/iszero.h
new file mode 100644
index 0000000..331614c
--- /dev/null
+++ b/common/include/iszero.h
@@ -0,0 +1,60 @@
+/* nbdkit
+ * Copyright (C) 2018 Red Hat Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Red Hat nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef NBDKIT_ISZERO_H
+#define NBDKIT_ISZERO_H
+
+#include <string.h>
+#include <stdbool.h>
+
+/* Return true iff the buffer is all zero bytes.
+ *
+ * The clever approach here was suggested by Eric Blake.  See:
+ * https://www.redhat.com/archives/libguestfs/2017-April/msg00171.html
+ */
+static inline bool
+is_zero (const char *buffer, size_t size)
+{
+  size_t i;
+  const size_t limit = size < 16 ? size : 16;
+
+  for (i = 0; i < limit; ++i)
+    if (buffer[i])
+      return false;
+  if (size != limit)
+    return ! memcmp (buffer, buffer + 16, size - 16);
+
+  return true;
+}
+
+#endif /* NBDKIT_ISZERO_H */
diff --git a/configure.ac b/configure.ac
index b87efb9..774f290 100644
--- a/configure.ac
+++ b/configure.ac
@@ -538,6 +538,7 @@ AC_CONFIG_FILES([podwrapper.pl],
                 [chmod +x,-w podwrapper.pl])
 AC_CONFIG_FILES([Makefile
                  bash/Makefile
+                 common/include/Makefile
                  docs/Makefile
                  include/Makefile
                  plugins/Makefile
-- 
2.18.0

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