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qdict: implement a qdict_crumple method for un-flattening a dict

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The qdict_flatten() method will take a dict whose elements are
further nested dicts/lists and flatten them by concatenating
keys.

The qdict_crumple() method aims to do the reverse, taking a flat
qdict, and turning it into a set of nested dicts/lists. It will
apply nesting based on the key name, with a '.' indicating a
new level in the hierarchy. If the keys in the nested structure
are all numeric, it will create a list, otherwise it will create
a dict.

If the keys are a mixture of numeric and non-numeric, or the
numeric keys are not in strictly ascending order, an error will
be reported.

As an example, a flat dict containing

 {
   'foo.0.bar': 'one',
   'foo.0.wizz': '1',
   'foo.1.bar': 'two',
   'foo.1.wizz': '2'
 }

will get turned into a dict with one element 'foo' whose
value is a list. The list elements will each in turn be
dicts.

 {
   'foo': [
     { 'bar': 'one', 'wizz': '1' },
     { 'bar': 'two', 'wizz': '2' }
   ],
 }

If the key is intended to contain a literal '.', then it must
be escaped as '..'. ie a flat dict

  {
     'foo..bar': 'wizz',
     'bar.foo..bar': 'eek',
     'bar.hello': 'world'
  }

Will end up as

  {
     'foo.bar': 'wizz',
     'bar': {
        'foo.bar': 'eek',
        'hello': 'world'
     }
  }

The intent of this function is that it allows a set of QemuOpts
to be turned into a nested data structure that mirrors the nesting
used when the same object is defined over QMP.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1475246744-29302-3-git-send-email-berrange@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Parameter recursive dropped along with its tests; whitespace style
touched up]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Daniel P. Berrange 2016-09-30 15:45:25 +01:00 • committed by Markus Armbruster
parent b1d2e5f1b0
commit 603476c25c
3 changed files with 428 additions and 8 deletions
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277
qobject/qdict.c
View file

@ -17,6 +17,7 @@
#include "qapi/qmp/qbool.h"
#include "qapi/qmp/qstring.h"
#include "qapi/qmp/qobject.h"
#include "qapi/error.h"
#include "qemu/queue.h"
#include "qemu-common.h"
#include "qemu/cutils.h"
@ -683,6 +684,282 @@ void qdict_array_split(QDict *src, QList **dst)
}
}
/**
* qdict_split_flat_key:
* @key: the key string to split
* @prefix: non-NULL pointer to hold extracted prefix
* @suffix: non-NULL pointer to remaining suffix
*
* Given a flattened key such as 'foo.0.bar', split it into two parts
* at the first '.' separator. Allows double dot ('..') to escape the
* normal separator.
*
* e.g.
* 'foo.0.bar' -> prefix='foo' and suffix='0.bar'
* 'foo..0.bar' -> prefix='foo.0' and suffix='bar'
*
* The '..' sequence will be unescaped in the returned 'prefix'
* string. The 'suffix' string will be left in escaped format, so it
* can be fed back into the qdict_split_flat_key() key as the input
* later.
*
* The caller is responsible for freeing the string returned in @prefix
* using g_free().
*/
static void qdict_split_flat_key(const char *key, char **prefix,
const char **suffix)
{
const char *separator;
size_t i, j;
/* Find first '.' separator, but if there is a pair '..'
* that acts as an escape, so skip over '..' */
separator = NULL;
do {
if (separator) {
separator += 2;
} else {
separator = key;
}
separator = strchr(separator, '.');
} while (separator && separator[1] == '.');
if (separator) {
*prefix = g_strndup(key, separator - key);
*suffix = separator + 1;
} else {
*prefix = g_strdup(key);
*suffix = NULL;
}
/* Unescape the '..' sequence into '.' */
for (i = 0, j = 0; (*prefix)[i] != '\0'; i++, j++) {
if ((*prefix)[i] == '.') {
assert((*prefix)[i + 1] == '.');
i++;
}
(*prefix)[j] = (*prefix)[i];
}
(*prefix)[j] = '\0';
}
/**
* qdict_is_list:
* @maybe_list: dict to check if keys represent list elements.
*
* Determine whether all keys in @maybe_list are valid list elements.
* If @maybe_list is non-zero in length and all the keys look like
* valid list indexes, this will return 1. If @maybe_list is zero
* length or all keys are non-numeric then it will return 0 to indicate
* it is a normal qdict. If there is a mix of numeric and non-numeric
* keys, or the list indexes are non-contiguous, an error is reported.
*
* Returns: 1 if a valid list, 0 if a dict, -1 on error
*/
static int qdict_is_list(QDict *maybe_list, Error **errp)
{
const QDictEntry *ent;
ssize_t len = 0;
ssize_t max = -1;
int is_list = -1;
int64_t val;
for (ent = qdict_first(maybe_list); ent != NULL;
ent = qdict_next(maybe_list, ent)) {
if (qemu_strtoll(ent->key, NULL, 10, &val) == 0) {
if (is_list == -1) {
is_list = 1;
} else if (!is_list) {
error_setg(errp,
"Cannot mix list and non-list keys");
return -1;
}
len++;
if (val > max) {
max = val;
}
} else {
if (is_list == -1) {
is_list = 0;
} else if (is_list) {
error_setg(errp,
"Cannot mix list and non-list keys");
return -1;
}
}
}
if (is_list == -1) {
assert(!qdict_size(maybe_list));
is_list = 0;
}
/* NB this isn't a perfect check - e.g. it won't catch
* a list containing '1', '+1', '01', '3', but that
* does not matter - we've still proved that the
* input is a list. It is up the caller to do a
* stricter check if desired */
if (len != (max + 1)) {
error_setg(errp, "List indices are not contiguous, "
"saw %zd elements but %zd largest index",
len, max);
return -1;
}
return is_list;
}
/**
* qdict_crumple:
* @src: the original flat dictionary (only scalar values) to crumple
*
* Takes a flat dictionary whose keys use '.' separator to indicate
* nesting, and values are scalars, and crumples it into a nested
* structure.
*
* To include a literal '.' in a key name, it must be escaped as '..'
*
* For example, an input of:
*
* { 'foo.0.bar': 'one', 'foo.0.wizz': '1',
* 'foo.1.bar': 'two', 'foo.1.wizz': '2' }
*
* will result in an output of:
*
* {
* 'foo': [
* { 'bar': 'one', 'wizz': '1' },
* { 'bar': 'two', 'wizz': '2' }
* ],
* }
*
* The following scenarios in the input dict will result in an
* error being returned:
*
* - Any values in @src are non-scalar types
* - If keys in @src imply that a particular level is both a
* list and a dict. e.g., "foo.0.bar" and "foo.eek.bar".
* - If keys in @src imply that a particular level is a list,
* but the indices are non-contiguous. e.g. "foo.0.bar" and
* "foo.2.bar" without any "foo.1.bar" present.
* - If keys in @src represent list indexes, but are not in
* the "%zu" format. e.g. "foo.+0.bar"
*
* Returns: either a QDict or QList for the nested data structure, or NULL
* on error
*/
QObject *qdict_crumple(const QDict *src, Error **errp)
{
const QDictEntry *ent;
QDict *two_level, *multi_level = NULL;
QObject *dst = NULL, *child;
size_t i;
char *prefix = NULL;
const char *suffix = NULL;
int is_list;
two_level = qdict_new();
/* Step 1: split our totally flat dict into a two level dict */
for (ent = qdict_first(src); ent != NULL; ent = qdict_next(src, ent)) {
if (qobject_type(ent->value) == QTYPE_QDICT ||
qobject_type(ent->value) == QTYPE_QLIST) {
error_setg(errp, "Value %s is not a scalar",
ent->key);
goto error;
}
qdict_split_flat_key(ent->key, &prefix, &suffix);
child = qdict_get(two_level, prefix);
if (suffix) {
if (child) {
if (qobject_type(child) != QTYPE_QDICT) {
error_setg(errp, "Key %s prefix is already set as a scalar",
prefix);
goto error;
}
} else {
child = QOBJECT(qdict_new());
qdict_put_obj(two_level, prefix, child);
}
qobject_incref(ent->value);
qdict_put_obj(qobject_to_qdict(child), suffix, ent->value);
} else {
if (child) {
error_setg(errp, "Key %s prefix is already set as a dict",
prefix);
goto error;
}
qobject_incref(ent->value);
qdict_put_obj(two_level, prefix, ent->value);
}
g_free(prefix);
prefix = NULL;
}
/* Step 2: optionally process the two level dict recursively
* into a multi-level dict */
multi_level = qdict_new();
for (ent = qdict_first(two_level); ent != NULL;
ent = qdict_next(two_level, ent)) {
if (qobject_type(ent->value) == QTYPE_QDICT) {
child = qdict_crumple(qobject_to_qdict(ent->value), errp);
if (!child) {
goto error;
}
qdict_put_obj(multi_level, ent->key, child);
} else {
qobject_incref(ent->value);
qdict_put_obj(multi_level, ent->key, ent->value);
}
}
QDECREF(two_level);
two_level = NULL;
/* Step 3: detect if we need to turn our dict into list */
is_list = qdict_is_list(multi_level, errp);
if (is_list < 0) {
goto error;
}
if (is_list) {
dst = QOBJECT(qlist_new());
for (i = 0; i < qdict_size(multi_level); i++) {
char *key = g_strdup_printf("%zu", i);
child = qdict_get(multi_level, key);
g_free(key);
if (!child) {
error_setg(errp, "Missing list index %zu", i);
goto error;
}
qobject_incref(child);
qlist_append_obj(qobject_to_qlist(dst), child);
}
QDECREF(multi_level);
multi_level = NULL;
} else {
dst = QOBJECT(multi_level);
}
return dst;
error:
g_free(prefix);
QDECREF(multi_level);
QDECREF(two_level);
qobject_decref(dst);
return NULL;
}
/**
* qdict_array_entries(): Returns the number of direct array entries if the
* sub-QDict of src specified by the prefix in subqdict (or src itself for