Re: [Qemu-devel] [PATCH V10 12/13] quorum: Add quorum_open() and quorum_close().

[Max Reitz]

On 28.01.2014 17:52, Benoît Canet wrote:
> From: Benoît Canet <address@hidden>
>
> Example of command line:
> -drive if=virtio,file.driver=quorum,\
> file.children.0.file.filename=1.raw,\
> file.children.0.node-name=1.raw,\
> file.children.0.driver=raw,\
> file.children.1.file.filename=2.raw,\
> file.children.1.node-name=2.raw,\
> file.children.1.driver=raw,\
> file.children.2.file.filename=3.raw,\
> file.children.2.node-name=3.raw,\
> file.children.2.driver=raw,\
> file.vote_threshold=2
>
> file.blkverify=on with file.vote_threshold=2 and two files can be passed to
> emulated blkverify.
>
> Signed-off-by: Benoit Canet <address@hidden>
> ---
>   block/quorum.c   | 308 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   qapi-schema.json |  21 +++-
>   2 files changed, 328 insertions(+), 1 deletion(-)
>
> diff --git a/block/quorum.c b/block/quorum.c
> index e7b2090..0c0d630 100644
> --- a/block/quorum.c
> +++ b/block/quorum.c
> @@ -17,8 +17,12 @@
>   #include <gnutls/crypto.h>
>   #include "block/block_int.h"
>   #include "qapi/qmp/qjson.h"
> +#include "qapi/qmp/types.h"
> +#include "qemu-common.h"
>   
>   #define HASH_LENGTH 32
> +#define KEY_PREFIX "children."
> +#define KEY_FILENAME_SUFFIX ".file.filename"
>   
>   /* This union holds a vote hash value */
>   typedef union QuorumVoteValue {
> @@ -702,12 +706,316 @@ static bool 
> quorum_recurse_is_first_non_filter(BlockDriverState *bs,
>       return false;
>   }

Perhaps you could make use of qdict_extract_subqdict() and 
qdict_array_split() functions here...? That is, 
qdict_extract_subqdict(..., "children.") and then qdict_array_split() on 
the result?

> +static int quorum_match_key(const char *key,
> +                            char **key_prefix)
> +{
> +    const char *start;
> +    char *next;
> +    unsigned long long idx;
> +    int ret;
> +
> +    *key_prefix = NULL;
> +
> +    /* the following code is a translation of the following pseudo code:
> +     *       match = key.match('(^children\.(\d+)\.)$suffix)
> +     *       if not match:
> +     *           return -1;
> +     *       key_prefix = match.outer_match()
> +     *       idx = match.inner_match()
> +     *
> +     * note: we also match the .file suffix to avoid futher checkings
> +     */
> +
> +    /* this key is not a child */
> +    if (strncmp(key, KEY_PREFIX, strlen(KEY_PREFIX))) {
> +        return -1;
> +    }
> +
> +    /* take first char after prefix */
> +    start = key + strlen(KEY_PREFIX);
> +
> +    /* if the string end here -> scan fail */
> +    if (start[0] == '\0') {
> +        return -1;
> +    }
> +
> +    /* try to retrieve the index */
> +    ret = parse_uint(start, &idx, &next, 10);
> +
> +    /* no int found -> scan fail */
> +    if (ret < 0) {
> +        return -1;
> +    }
> +
> +    /* we are taking a reference via QMP */
> +    if (next - key == strlen(key)) {

"if (!*next)" would probably accomplish the same (or "if next[0] == 
'\0')" to keep your coding style) without having to call strlen().

> +        *key_prefix = g_strdup(key);
> +        return idx;
> +    }
> +
> +    /* match the suffix to avoid matching the same idx
> +     * multiple times and be required to do more checks later
> +     */
> +    if (strncmp(next, KEY_FILENAME_SUFFIX, strlen(KEY_FILENAME_SUFFIX))) {

As stated in my review from October, you may use sizeof() to avoid strlen().

> +        return -1;
> +    }
> +
> +    /* do not include '.' */
> +    int len = next - key;
> +    *key_prefix = g_strndup(key, len);
> +
> +    return idx;
> +}
> +
> +static QDict *quorum_get_children_idx(const QDict *options)
> +{
> +    const QDictEntry *ent;
> +    QDict *result;
> +    char *key_prefix;
> +    int idx;
> +
> +    result = qdict_new();
> +
> +    for (ent = qdict_first(options); ent; ent = qdict_next(options, ent)) {
> +        const char *key = qdict_entry_key(ent);
> +        idx = quorum_match_key(key,
> +                               &key_prefix);
> +
> +        /* if the result zero or positive we got a key */
> +        if (idx < 0) {
> +            continue;
> +        }
> +
> +        qdict_put(result, key_prefix, qint_from_int(idx));
> +    }
> +
> +    return result;
> +}
> +
> +static int quorum_fill_validation_array(bool *array,
> +                                        const QDict *dict,
> +                                        int total,
> +                                        Error **errp)
> +{
> +    const QDictEntry *ent;
> +
> +    /* fill the checking array with children indexes */
> +    for (ent = qdict_first(dict); ent; ent = qdict_next(dict, ent)) {
> +        const char *key = qdict_entry_key(ent);
> +        int idx = qdict_get_int(dict, key);
> +
> +        if (idx < 0 || idx >= total) {
> +            error_setg(errp,
> +                "Children index must be between 0 and children count -1");

Quote from October: I'd prefer "- 1" instead of "-1" (or even "Child 
index must be an unsigned integer smaller than the children count").

> +            return -ERANGE;
> +        }
> +
> +        array[idx] = true;
> +    }
> +
> +    return 0;
> +}
> +
> +static int quorum_valid_indexes(const bool *array, int total, Error **errp)
> +{
> +    int i;
> +
> +    for (i = 0; i < total; i++) {
> +        if (array[i] == true) {
> +            continue;
> +        }
> +
> +        error_setg(errp,
> +            "All child indexes between 0 and children count -1  must be "
> +            " used");

Again, I'd prefer "- 1"; then, there are two spaces to the left of 
"must" and two spaces after "be".

> +        return -ERANGE;
> +    }
> +
> +    return 0;
> +}
> +
> +static int quorum_valid_children_indexes(const QDict *dict,
> +                                         int total,
> +                                         Error **errp)
> +{
> +    bool *array;
> +    int ret = 0;;
> +
> +    /* allocate indexes checking array and put false in it */
> +    array = g_new0(bool, total);
> +
> +    ret = quorum_fill_validation_array(array, dict, total, errp);
> +    if (ret < 0) {
> +        goto free_exit;
> +    }
> +
> +    ret = quorum_valid_indexes(array, total, errp);
> +free_exit:
> +    g_free(array);
> +    return ret;
> +}
> +
> +static int quorum_valid_threshold(int threshold,
> +                                  int total,
> +                                  Error **errp)
> +{
> +
> +    if (threshold < 1) {
> +        error_set(errp, QERR_INVALID_PARAMETER_VALUE,
> +                  "vote-threshold", "value >= 1");
> +        return -ERANGE;
> +    }
> +
> +    if (threshold > total) {
> +        error_setg(errp, "threshold <= children count must be true");

Quote from October: Well, while this might technically be true, I'd 
rather go for "threshold may not exceed children count" instead. ;-)

> +        return -ERANGE;
> +    }
> +
> +    return 0;
> +}
> +
> +static int quorum_open(BlockDriverState *bs,
> +                       QDict *options,
> +                       int flags,
> +                       Error **errp)
> +{
> +    BDRVQuorumState *s = bs->opaque;
> +    Error *local_err = NULL;
> +    const QDictEntry *ent;
> +    QDict *idx_dict;
> +    bool *opened;
> +    const char *value;
> +    char *next;
> +    int i;
> +    int ret = 0;
> +
> +    /* get a dict of children indexes for validation */
> +    idx_dict = quorum_get_children_idx(options);
> +
> +    /* count how many different children indexes are present and validate */
> +    s->total = qdict_size(idx_dict);
> +    if (s->total < 2) {
> +        error_setg(&local_err,
> +                   "Number of provided children must be greater than 1");
> +        ret = -EINVAL;
> +        goto exit;
> +    }
> +
> +    /* validate that the set of index is coherent */
> +    ret = quorum_valid_children_indexes(idx_dict, s->total, &local_err);
> +    if (ret < 0) {
> +        goto exit;
> +    }
> +
> +    ret = qdict_get_try_int(options, "vote-threshold", -1);
> +    /* from QMP */
> +    if (ret != -1) {
> +        qdict_del(options, "vote-threshold");
> +        s->threshold = ret;
> +    /* from command line */
> +    } else {
> +        /* retrieve the threshold option from the command line */
> +        value = qdict_get_try_str(options, "vote_threshold");
> +        if (!value) {
> +            error_setg(&local_err,
> +                       "vote_threshold must be provided");
> +            ret = -EINVAL;
> +            goto exit;
> +        }
> +        qdict_del(options, "vote_threshold");
> +
> +        ret = parse_uint(value, (unsigned long long *) &s->threshold, &next, 
> 10);

I don't like this cast at all...

> +
> +        /* no int found -> scan fail */
> +        if (ret < 0) {
> +            error_setg(&local_err,
> +                       "invalid voter_threshold specified");

*vote_threshold

> +            ret = -EINVAL;
> +            goto exit;
> +        }
> +    }
> +
> +    /* and validate it againts s->total */

Still *against

> +    ret = quorum_valid_threshold(s->threshold, s->total, &local_err);
> +    if (ret < 0) {
> +        goto exit;
> +    }
> +
> +    /* is the driver in blkverify mode */
> +    value = qdict_get_try_str(options, "blkverify");
> +    if (value && !strcmp(value, "on")  &&
> +        s->total == 2 && s->threshold == 2) {
> +        s->is_blkverify = true;
> +    }

Quote from October: If the user specifies anything different from "on" 
or if he does and s->total or s->threshold is not 2, quorum will 
silently work in non-blkverify mode without telling the user. So I'd 
emit a message here if blkverify has been specified and its value is 
different from "off" but s->is_blkverify remains false (i.e., “else if 
(value && strcmp(value, "off")) { fprintf(stderr, "[Some warning]"); }”).

> +    qdict_del(options, "blkverify");
> +
> +    /* allocate the children BlockDriverState array */
> +    s->bs = g_new0(BlockDriverState *, s->total);
> +    opened = g_new0(bool, s->total);
> +
> +    /* open children bs */
> +    for (ent = qdict_first(idx_dict);
> +         ent; ent = qdict_next(idx_dict, ent)) {

This condition fits on a single line.

> +        const char *key = qdict_entry_key(ent);
> +        int idx = qdict_get_int(idx_dict, key);
> +        ret = bdrv_open_image(&s->bs[idx],
> +                              NULL,
> +                              options,
> +                              key,
> +                              flags,
> +                              false,
> +                              &local_err);

This takes two, but definitely not seven.

> +        if (ret < 0) {
> +            goto close_exit;
> +        }
> +        opened[idx] = true;
> +    }
> +
> +    g_free(opened);
> +    goto exit;
> +
> +close_exit:
> +    /* cleanup on error */
> +    for (i = 0; i < s->total; i++) {
> +        if (!opened[i]) {
> +            continue;
> +        }
> +        bdrv_close(s->bs[i]);

You'll probably want bdrv_unref() here.

> +    }
> +    g_free(s->bs);
> +    g_free(opened);
> +exit:
> +    /* propagate error */
> +    if (error_is_set(&local_err)) {
> +        error_propagate(errp, local_err);
> +    }
> +    return ret;
> +}
> +
> +static void quorum_close(BlockDriverState *bs)
> +{
> +    BDRVQuorumState *s = bs->opaque;
> +    int i;
> +
> +    for (i = 0; i < s->total; i++) {
> +        /* Ensure writes reach stable storage */
> +        bdrv_flush(s->bs[i]);
> +        /* close manually because we'll free s->bs */
> +        bdrv_close(s->bs[i]);

Again, bdrv_unref().

> +    }
> +
> +    g_free(s->bs);
> +}
> +
>   static BlockDriver bdrv_quorum = {
>       .format_name        = "quorum",
>       .protocol_name      = "quorum",
>   
>       .instance_size      = sizeof(BDRVQuorumState),
>   
> +    .bdrv_file_open     = quorum_open,
> +    .bdrv_close         = quorum_close,
> +
>       .bdrv_co_flush_to_disk = quorum_co_flush,
>   
>       .bdrv_getlength     = quorum_getlength,
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 05ced9d..903a3a0 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -4352,6 +4352,24 @@
>               'raw': 'BlockdevRef' } }
>   
>   ##
> +# @BlockdevOptionsQuorum
> +#
> +# Driver specific block device options for Quorum
> +#
> +# @blkverify:      #optional true if the driver must print content mismatch
> +#
> +# @children:       the children block device to use
> +#
> +# @vote_threshold: the vote limit under which a read will fail
> +#
> +# Since: 2.0
> +##
> +{ 'type': 'BlockdevOptionsQuorum',
> +  'data': { '*blkverify': 'bool',
> +            'children': [ 'BlockdevRef' ],
> +            'vote-threshold': 'int' } }
> +
> +##
>   # @BlockdevOptions
>   #
>   # Options for creating a block device.
> @@ -4389,7 +4407,8 @@
>         'vdi':        'BlockdevOptionsGenericFormat',
>         'vhdx':       'BlockdevOptionsGenericFormat',
>         'vmdk':       'BlockdevOptionsGenericCOWFormat',
> -      'vpc':        'BlockdevOptionsGenericFormat'
> +      'vpc':        'BlockdevOptionsGenericFormat',
> +      'quorum':     'BlockdevOptionsQuorum'
>     } }
>   
>   ##

As I've said before, I'd really like it if you could abandon all those 
functions for parsing the incoming options QDict in favor of 
qdict_extract_subqdict() and qdict_array_split() which will most likely 
do the job just fine; and, in fact, I have written qdict_array_split() 
with Quorum in mind. ;-)

Max