Re: [Qemu-devel] [PATCH 03/24] keyval: New keyval_parse()

[Kevin Wolf <kwolf@redhat.com>]

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.

> * 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 <armbru@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 <armbru@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.

> + *             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/ ?

> + *
> + * 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.

> + */
> +
> +#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.

> +    }
> +    return s;
> +}

Kevin