Re: [Qemu-devel] [PATCH 01/34] qdict: Add qdict_array_entries()

[Kevin Wolf <kwolf@redhat.com>]

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Am 08.05.2015 um 22:06 hat Eric Blake geschrieben:
> On 05/08/2015 11:21 AM, Kevin Wolf wrote:
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> 
> Might want to include mention of what it will be used for in the commit
> body.

You're right. This is the new commit message:

    This counts the entries in a flattened array in a QDict without
    actually splitting the QDict into a QList.

    bdrv_open_image() doesn't take a QList, but rather a QDict and a key
    prefix string, so this is more convenient for block drivers which have a
    dynamically sized list of child nodes (e.g. Quorum) and are to be
    converted to using bdrv_open_image() as the standard interface for
    opening child nodes.

> >  include/qapi/qmp/qdict.h |  1 +
> >  qobject/qdict.c          | 68 +++++++++++++++++++++++++++++++++++++++++++++---
> >  2 files changed, 65 insertions(+), 4 deletions(-)
> > 
> 
> > @@ -646,7 +647,7 @@ void qdict_array_split(QDict *src, QList **dst)
> >          snprintf_ret = snprintf(prefix, 32, "%u.", i);
> >          assert(snprintf_ret < 32);
> >  
> > -        is_subqdict = qdict_has_prefixed_entries(src, prefix);
> > +        is_subqdict = qdict_count_prefixed_entries(src, prefix);
> 
> Good thing we require a C99 compiler, where 'bool = int' does the right
> thing for integers > 1.
> 
> >  /**
> > + * qdict_array_valid(): Returns the number of direct array entries if the
> > + * sub-QDict of src specified by the prefix in subqdict (or src itself for
> > + * prefix == "") is valid as an array, i.e. the length of the created list if
> > + * the sub-QDict would become empty after calling qdict_array_split() on it. If
> > + * the array is not valid, -1 is returned.
> > + */
> > +int qdict_array_entries(QDict *src, const char *subqdict)
> 
> Comment doesn't match function name.

Thanks, fixed.

> > +{
> > +    const QDictEntry *entry;
> > +    unsigned i;
> > +    unsigned entries = 0;
> > +    size_t subqdict_len = strlen(subqdict);
> > +
> > +    assert(!subqdict_len || subqdict[subqdict_len - 1] == '.');
> > +
> > +    for (i = 0; i < UINT_MAX; i++) {
> > +        QObject *subqobj;
> > +        int subqdict_entries;
> > +        size_t slen = 32 + subqdict_len;
> > +        char indexstr[slen], prefix[slen];
> 
> And more dependence on a working C99 compiler, thanks to variable length
> array (VLA).
> 
> > +        size_t snprintf_ret;
> > +
> > +        snprintf_ret = snprintf(indexstr, slen, "%s%u", subqdict, i);
> > +        assert(snprintf_ret < slen);
> 
> Since gcc may compile the allocation of indexstr into a malloc()
> anyways, would it be any simpler to just use g_strdup_printf() directly,
> instead of futzing around with VLA and snprintf() ourselves?  It might
> mean less code, as some of the error checking is taken care of on your
> behalf.

This code parallels the code in qdict_array_split(), which looks almos
the same, except that the latter doesn't support subqict and therefore
has a fixed-size array rather than a VLA.

If you think that g_strdup_printf() is preferable, I would do that on
top of this series and change both functions.

Kevin

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