[libvirt] [RFC PATCH 01/12] util: storage: Split out useful bits of virStorageFileParseChainIndex

[Eric Blake]

On 02/23/2017 01:21 PM, Peter Krempa wrote:
> The function has very specific semantics. Split out the part that parses
> the backing store specification string into a separate helper so that it
> can be reused later while keeping the wrapper with existing semantics.
> 
> Note that virStorageFileParseChainIndex is pretty well covered by the
> test suite.
> ---
>  src/libvirt_private.syms  |  1 +
>  src/util/virstoragefile.c | 68 +++++++++++++++++++++++++++++++++++++++--------
>  src/util/virstoragefile.h |  5 ++++
>  3 files changed, 63 insertions(+), 11 deletions(-)
> 
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index 07a35333b..69d1bc860 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -2462,6 +2462,7 @@ virStorageFileGetMetadataInternal;
>  virStorageFileGetRelativeBackingPath;
>  virStorageFileGetSCSIKey;
>  virStorageFileIsClusterFS;
> +virStorageFileParseBackingStoreStr;
>  virStorageFileParseChainIndex;
>  virStorageFileProbeFormat;
>  virStorageFileResize;
> diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
> index c9420fdb7..3e711228b 100644
> --- a/src/util/virstoragefile.c
> +++ b/src/util/virstoragefile.c
> @@ -1442,32 +1442,78 @@ int virStorageFileGetSCSIKey(const char *path,
>  }
>  #endif
> 
> +
> +/**
> + * virStorageFileParseBackingStoreStr:
> + * @str: backing store specifier string to parse
> + * @target: returns target device portion of the string
> + * @chainIndex: returns the backing store portion of the string
> + *
> + * Parses the backing store specifier string such as vda[1], or sda into
> + * components and returns them via arguments. If the string did not specify an
> + * index 0 is assumed.

grammar nit: s/index/index,/

> + *
> + * Returns 0 on success -1 on error
> + */
> +int
> +virStorageFileParseBackingStoreStr(const char *str,
> +                                   char **target,
> +                                   unsigned int *chainIndex)
> +{
> +    char **strings = NULL;
> +    size_t nstrings;
> +    unsigned int idx = 0;
> +    char *suffix;
> +    int ret = -1;
> +
> +    *chainIndex = 0;
> +
> +    if (!(strings = virStringSplitCount(str, "[", 2, &nstrings)))
> +        return -1;
> +
> +    if (nstrings == 2) {
> +        if (virStrToLong_uip(strings[1], &suffix, 10, &idx) < 0 ||
> +            STRNEQ(suffix, "]"))
> +            goto cleanup;
> +    }
> +
> +    if (target &&
> +        VIR_STRDUP(*target, strings[0]) < 0)
> +        goto cleanup;
> +
> +    *chainIndex = idx;
> +    ret = 0;
> +
> + cleanup:
> +    virStringListFreeCount(strings, nstrings);
> +    return ret;
> +}

I might have gone for a simpler implementation (no need to malloc and
throw away a full-blown string split, when it is easy to do by hand):

char *p = strchr(str, '[');
char *suffix;
int ret = 0;

*chainIndex = 0;
if (!p) {
    if (target)
        ret = VIR_STRDUP(*target, str);
} else if (virStrToLong_uip(p + 1, &suffix, 10, chainIndex) < 0 ||
           STRNEQ(suffix, "]")) {
    return -1;
} else if (target) {
    ret = VIR_STRNDUP(*target, str, p - str);
}
return ret;

(well, modulo a tweak to the return value if returning 0 is more
important than returning 1 on success)

I see that you were just moving the pre-existing complexity, though.  At
any rate, it's a nice refactoring, whether or not you also improve the
new helper function to not be so roundabout at computing its results.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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