Kevin Wolf <kw...@redhat.com> writes:
> Am 27.02.2017 um 12:20 hat Markus Armbruster geschrieben:
>> keyval_parse() parses KEY=VALUE,... into a QDict. Works like
>> qemu_opts_parse(), except:
>>
>> * Returns a QDict instead of a QemuOpts (d'oh).
>>
>> * Supports nesting, unlike QemuOpts: a KEY is split into key
>> fragments at '.' (dotted key convention; the block layer does
>> something similar on top of QemuOpts). The key fragments are QDict
>> keys, and the last one's value is updated to VALUE.
>>
>> * Each key fragment may be up to 127 bytes long. qemu_opts_parse()
>> limits the entire key to 127 bytes.
>>
>> * Overlong key fragments are rejected. qemu_opts_parse() silently
>> truncates them.
>>
>> * Empty key fragments are rejected. qemu_opts_parse() happily
>> accepts empty keys.
>>
>> * It does not store the returned value. qemu_opts_parse() stores it
>> in the QemuOptsList.
>>
>> * It does not treat parameter "id" specially. qemu_opts_parse()
>> ignores all but the first "id", and fails when its value isn't
>> id_wellformed(), or duplicate (a QemuOpts with the same ID is
>> already stored). It also screws up when a value contains ",id=".
>
> This is important to keep in mind, callers need to explicitly check
> validity of the "id" key themselves.
Good point. Come to think of it, I'm not sure I did %-}
>> * Implied value is not supported. qemu_opts_parse() desugars "foo" to
>> "foo=on", and "nofoo" to "foo=off".
>>
>> * An implied key's value can't be empty, and can't contain ','.
>>
>> I intend to grow this into a saner replacement for QemuOpts. It'll
>> take time, though.
>>
>> Note: keyval_parse() provides no way to do lists, and its key syntax
>> is incompatible with the __RFQDN_ prefix convention for downstream
>> extensions, because it blindly splits at '.', even in __RFQDN_. Both
>> issues will be addressed later in the series.
>>
>> Signed-off-by: Markus Armbruster <arm...@redhat.com>
>
>> diff --git a/util/keyval.c b/util/keyval.c
>> new file mode 100644
>> index 0000000..3904c39
>> --- /dev/null
>> +++ b/util/keyval.c
>> @@ -0,0 +1,228 @@
>> +/*
>> + * Parsing KEY=VALUE,... strings
>> + *
>> + * Copyright (C) 2017 Red Hat Inc.
>> + *
>> + * Authors:
>> + * Markus Armbruster <arm...@redhat.com>,
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +/*
>> + * KEY=VALUE,... syntax:
>> + *
>> + * key-vals = [ key-val { ',' key-vals } ]
>> + * key-val = key '=' val
>> + * key = key-fragment { '.' key-fragment }
>> + * key-fragment = / [^=,.]* /
>> + * val = { / [^,]* / | ',,' }
>> + *
>> + * Semantics defined by reduction to JSON:
>> + *
>> + * key-vals defines a tree of objects rooted at R
>> + * where for each key-val = key-fragment . ... = val in key-vals
>> + * R op key-fragment op ... = val'
>> + * where (left-associative) op is member reference L.key-fragment
>
> Maybe it's just me, but I can't say that I fully understand what these
> last two lines are supposed to tell me.
Okay, I'll try to clarify.
Last patch amends this part for lists.
>> + * val' is val with ',,' replaced by ','
>> + * and only R may be empty.
>> + *
>> + * Duplicate keys are permitted; all but the last one are ignored.
>> + *
>> + * The equations must have a solution. Counter-example: a.b=1,a=2
>> + * doesn't have one, because R.a must be an object to satisfy a.b=1
>> + * and a string to satisfy a=2.
>> + *
>> + * The length of any key-fragment must be between 1 and 127.
>> + *
>> + * Design flaw: there is no way to denote an empty non-root object.
>> + * While interpreting "key absent" as empty object seems natural
>> + * (removing a key-val from the input string removes the member when
>> + * there are more, so why not when it's the last), it doesn't work:
>> + * "key absent" already means "optional object absent", which isn't
>> + * the same as "empty object present".
>> + *
>> + * Additional syntax for use with an implied key:
>> + *
>> + * key-vals-ik = val-no-key [ ',' key-vals ]
>> + * val-no-key = / [^,]* /
>> + *
>> + * where no-key is syntactic sugar for implied-key=val-no-key.
>
> s/no-key/val-no-key/ ?
Yes.
>> + *
>> + * TODO support lists
>> + * TODO support key-fragment with __RFQDN_ prefix (downstream extensions)
>
> Worth another TODO comment for implied values that contain a comma? The
> current restriction feels a bit artificial.
My reasons for the restriction are perhaps best explained with an
example. Consider params = "a,,,b".
qemu_opts_parse(opt_list, params, true) splits into comma-separated
parts like this:
# part key value
0 "a,," implied "a,"
1 "b" "b" "on"
qemu_opts_parse(list, params, false) like this:
# part key value
0 "a" "a" "on"
1 "" "" "on"
2 "" "" "on"
3 "b" "b" "on"
The split of depends on the permit_abbrev argument! I consider that
tasteless design. Or rather I would if I could bring myself to believe
in the existence of a design here.
The big hammer to make *syntactic* analysis invariant of whether we have
an implied key is to outlaw ',' val-no-key. That way, the leftmost part
of param can be isolated the same with and without implied key: it ends
at the first '=' or ','.
Perhaps a smaller hammer can be found, but right now I'm in no mood for
checking grammars for ambiguity :)
>> + */
>> +
>> +#include "qemu/osdep.h"
>> +#include "qapi/error.h"
>> +#include "qapi/qmp/qstring.h"
>> +#include "qemu/option.h"
>> +
>> +/*
>> + * Ensure @cur maps @key_in_cur the right way.
>> + * If @value is null, it needs to map to a QDict, else to this
>> + * QString.
>> + * If @cur doesn't have @key_in_cur, put an empty QDict or @value,
>> + * respectively.
>> + * Else, if it needs to map to a QDict, and already does, do nothing.
>> + * Else, if it needs to map to this QString, and already maps to a
>> + * QString, replace it by @value.
>> + * Else, fail because we have conflicting needs on how to map
>> + * @key_in_cur.
>> + * Use @key up to @key_cursor to identify the key in error messages.
>> + * On success, return the mapped value.
>> + * On failure, store an error through @errp and return NULL.
>> + */
>> +static QObject *keyval_parse_put(QDict *cur,
>> + const char *key_in_cur, QString *value,
>> + const char *key, const char *key_cursor,
>> + Error **errp)
>> +{
>> + QObject *old, *new;
>> +
>> + old = qdict_get(cur, key_in_cur);
>> + if (old) {
>> + if (qobject_type(old) != (value ? QTYPE_QSTRING : QTYPE_QDICT)) {
>> + error_setg(errp, "Parameters '%.*s.*' used inconsistently",
>> + (int)(key_cursor - key), key);
>> + return NULL;
>> + }
>> + if (!value) {
>> + return old; /* already QDict, do nothing */
>> + }
>> + new = QOBJECT(value); /* replacement */
>> + } else {
>> + new = QOBJECT(value) ?: QOBJECT(qdict_new());
>> + }
>> + qdict_put_obj(cur, key_in_cur, new);
>> + return new;
>> +}
>> +
>> +/*
>> + * Parse one KEY=VALUE from @params, store result in @qdict.
>> + * The first fragment of KEY applies to @qdict. Subsequent fragments
>> + * apply to nested QDicts, which are created on demand. @implied_key
>> + * is as in keyval_parse().
>> + * On success, return a pointer to the next KEY=VALUE, or else to '\0'.
>> + * On failure, return NULL.
>> + */
>> +static const char *keyval_parse_one(QDict *qdict, const char *params,
>> + const char *implied_key,
>> + Error **errp)
>> +{
>> + const char *key, *key_end, *s;
>> + size_t len;
>> + char key_in_cur[128];
>> + QDict *cur;
>> + QObject *next;
>> + QString *val;
>> +
>> + key = params;
>> + len = strcspn(params, "=,");
>> + if (implied_key && len && key[len] != '=') {
>> + /* Desugar implied key */
>> + key = implied_key;
>> + len = strlen(implied_key);
>> + }
>> + key_end = key + len;
>> +
>> + /*
>> + * Loop over key fragments: @s points to current fragment, it
>> + * applies to @cur. @key_in_cur[] holds the previous fragment.
>> + */
>> + cur = qdict;
>> + s = key;
>> + for (;;) {
>> + for (len = 0; s + len < key_end && s[len] != '.'; len++) {
>> + }
>> + if (!len) {
>> + assert(key != implied_key);
>> + error_setg(errp, "Invalid parameter '%.*s'",
>> + (int)(key_end - key), key);
>> + return NULL;
>> + }
>> + if (len >= sizeof(key_in_cur)) {
>> + assert(key != implied_key);
>> + error_setg(errp, "Parameter%s '%.*s' is too long",
>> + s != key || s + len != key_end ? " fragment" : "",
>> + (int)len, s);
>> + return NULL;
>> + }
>> +
>> + if (s != key) {
>> + next = keyval_parse_put(cur, key_in_cur, NULL,
>> + key, s - 1, errp);
>> + if (!next) {
>> + return NULL;
>> + }
>> + cur = qobject_to_qdict(next);
>> + assert(cur);
>> + }
>> +
>> + memcpy(key_in_cur, s, len);
>> + key_in_cur[len] = 0;
>> + s += len;
>> +
>> + if (*s != '.') {
>> + break;
>> + }
>> + s++;
>> + }
>> +
>> + if (key == implied_key) {
>> + assert(!*s);
>> + s = params;
>> + } else {
>> + if (*s != '=') {
>> + error_setg(errp, "Expected '=' after parameter '%.*s'",
>> + (int)(s - key), key);
>> + return NULL;
>> + }
>> + s++;
>> + }
>> +
>> + val = qstring_new();
>> + for (;;) {
>> + if (!*s) {
>> + break;
>> + } else if (*s == ',') {
>> + s++;
>> + if (*s != ',') {
>> + break;
>> + }
>> + }
>> + qstring_append_chr(val, *s++);
>> + }
>> +
>> + if (!keyval_parse_put(cur, key_in_cur, val, key, key_end, errp)) {
>> + return NULL;
>
> This leaks val.
Will fix, thanks!
>> + }
>> + return s;
>> +}
>
> Kevin
