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

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon,  7 Jun 2010 15:42:16 +0100
"Daniel P. Berrange" <berrange@redhat.com> wrote:

> 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"

 Missing license text.

> +
> +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 */