[Qemu-devel] [PATCH 03/19] Add enum handlers for easy & efficient string <-> int conversion

["Daniel P. Berrange" <berrange@redhat.com>]

There is quite alot of code using an enumeration of possible
values, which also needs todo conversions to/from a string
representation of enum values. These string <-> int conversions
have been repeated in an adhoc manner throughout the code.

This makes it hard to report on the list of valid strings,
eg in help output, or todo proper validation in the qemu
config/option parsing routines.

This addresses the first problem by introducing a standard
set of routines for performing string <-> int conversions
for enums. There are two restrictions on using these helpers,
the first enum value must be 0, and there must be a sentinal
in the enum to provide the max value.

For each enumeration, three functions will be made available

 - string to int convertor:

   int XXXX_from_string(const char *value);

   Returns -1 if the value was not an allowed string for the
   enumeration. Returns >= 0 for a valid value

 - int to string convertor

   const char * XXXX_to_string(int value);

   Returns NULL if the value was not a member of the
   enumeration. Returns a non-NULL sstring for valid value

 - string list generator

   char * XXXX_to_string_list(void);

   Returns a malloc'd string containing all valid values,
   separated by commas. Caller must free the string.

The general usage pattern is as follows.

In the header file (eg qemu-option.h):

  enum QemuOptType {
    QEMU_OPT_STRING = 0,  /* no parsing (use string as-is)                        */
    QEMU_OPT_BOOL,        /* on/off                                               */
    QEMU_OPT_NUMBER,      /* simple number                                        */
    QEMU_OPT_SIZE,        /* size, accepts (K)ilo, (M)ega, (G)iga, (T)era postfix */

    QEMU_OPT_LAST
  };
  QEMU_ENUM_DECL(qemu_opt_type);

This declares the function prototypes for the 3 methods
outlined above.

In the corresponding source file (eg qemu-option.c):

  QEMU_ENUM_IMPL(qemu_opt_type,
                 QEMU_OPT_LAST,
                 "string", "bool", "number", "size");

This provides the implementation of the 3 methods. If there
are greater/fewer strings provided than the number of values
in the  enumeration, this generates a compile time assertion
failure that looks like

  qemu-option.c:35: error: negative width in bit-field ‘verify_error_if_negative_size__’

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 Makefile.objs |    2 +-
 qemu-enum.c   |   44 ++++++++++++++++++++++++++++++++++++++++++++
 qemu-enum.h   |   45 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+), 1 deletions(-)
 create mode 100644 qemu-enum.c
 create mode 100644 qemu-enum.h

diff --git a/Makefile.objs b/Makefile.objs
index 9796dcb..0ba9966 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -8,7 +8,7 @@ qobject-obj-y += qerror.o
 # block-obj-y is code used by both qemu system emulation and qemu-img
 
 block-obj-y = cutils.o cache-utils.o qemu-malloc.o qemu-option.o module.o
-block-obj-y += nbd.o block.o aio.o aes.o osdep.o qemu-config.o
+block-obj-y += nbd.o block.o aio.o aes.o osdep.o qemu-config.o qemu-enum.o
 block-obj-$(CONFIG_POSIX) += posix-aio-compat.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
 
diff --git a/qemu-enum.c b/qemu-enum.c
new file mode 100644
index 0000000..9bb33ac
--- /dev/null
+++ b/qemu-enum.c
@@ -0,0 +1,44 @@
+#include "qemu-enum.h"
+
+int qemu_enum_from_string(const char *const*types,
+			  unsigned int ntypes,
+			  const char *type)
+{
+    unsigned int i;
+    if (!type)
+        return -1;
+
+    for (i = 0 ; i < ntypes ; i++)
+        if (strcmp(types[i], type) == 0)
+            return i;
+
+    return -1;
+}
+
+const char *qemu_enum_to_string(const char *const*types,
+				unsigned int ntypes,
+				int type)
+{
+    if (type < 0 || type >= ntypes)
+        return NULL;
+
+    return types[type];
+}
+
+char *qemu_enum_to_string_list(const char *const*types,
+			       unsigned int ntypes)
+{
+    size_t len = 0;
+    char *ret;
+    int i;
+    for (i = 0 ; i < ntypes ; i++)
+	len += strlen(types[i]) + 2;
+    ret = qemu_malloc(len);
+    *ret = '\0';
+    for (i = 0 ; i < ntypes ; i++) {
+	if (i > 0)
+	    strcat(ret, ", ");
+	strcat(ret, types[i]);
+    }
+    return ret;
+}
diff --git a/qemu-enum.h b/qemu-enum.h
new file mode 100644
index 0000000..ff47798
--- /dev/null
+++ b/qemu-enum.h
@@ -0,0 +1,45 @@
+#ifndef QEMU_ENUM_H
+#define QEMU_ENUM_H
+
+#include "qemu-common.h"
+#include "verify.h"
+
+
+int qemu_enum_from_string(const char *const*types,
+			  unsigned int ntypes,
+			  const char *type);
+
+const char *qemu_enum_to_string(const char *const*types,
+				unsigned int ntypes,
+				int type);
+
+char *qemu_enum_to_string_list(const char *const*types,
+			       unsigned int ntypes);
+
+#define QEMU_ENUM_IMPL(name, lastVal, ...)				\
+    static const char *const name ## _string_list[] = { __VA_ARGS__ };	\
+    char *name ## _to_string_list(void) {				\
+        return qemu_enum_to_string_list(name ## _string_list,		\
+					ARRAY_SIZE(name ## _string_list)); \
+    }                                                                   \
+    const char *name ## _to_string(int type) {				\
+        return qemu_enum_to_string(name ## _string_list,		\
+				   ARRAY_SIZE(name ## _string_list),	\
+				   type);				\
+    }                                                                   \
+    int name ## _from_string(const char *type) {			\
+        return qemu_enum_from_string(name ## _string_list,		\
+				     ARRAY_SIZE(name ## _string_list),	\
+				     type);				\
+    }									\
+    extern int (* name ## Verify (void))				\
+        [verify_true (ARRAY_SIZE(name ## _string_list) == lastVal)]
+
+# define QEMU_ENUM_DECL(name)				\
+    const char *name ## _to_string(int type);		\
+    char *name ## _to_string_list(void);		\
+    int name ## _from_string(const char*type)
+
+
+
+#endif /* QEMU_ENUM_H */
-- 
1.6.6.1