Re: [Qemu-devel] [PATCH 08/28] qcow2: Allow lazy refcounts to be enabled on the command line

[Paolo Bonzini <pbonzini@redhat.com>]

Il 15/03/2013 16:14, Stefan Hajnoczi ha scritto:
> From: Kevin Wolf <kwolf@redhat.com>
> 
> qcow2 images now accept a boolean lazy_refcounts options. Use it like
> this:
> 
>   -drive file=test.qcow2,lazy_refcounts=on
> 
> If the option is specified on the command line, it overrides the default
> specified by the qcow2 header flags that were set when creating the
> image.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/qcow2-cluster.c |  2 +-
>  block/qcow2.c         | 37 +++++++++++++++++++++++++++++++++++++
>  block/qcow2.h         |  1 +
>  3 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 56fccf9..ff9ae18 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -668,7 +668,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
>      }
>  
>      /* Update L2 table. */
> -    if (s->compatible_features & QCOW2_COMPAT_LAZY_REFCOUNTS) {
> +    if (s->use_lazy_refcounts) {
>          qcow2_mark_dirty(bs);
>      }
>      if (qcow2_need_accurate_refcounts(s)) {
> diff --git a/block/qcow2.c b/block/qcow2.c
> index f5e4269..ad43a13 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -285,11 +285,26 @@ static int qcow2_check(BlockDriverState *bs, BdrvCheckResult *result,
>      return ret;
>  }
>  
> +static QemuOptsList qcow2_runtime_opts = {
> +    .name = "qcow2",
> +    .head = QTAILQ_HEAD_INITIALIZER(qcow2_runtime_opts.head),
> +    .desc = {
> +        {
> +            .name = "lazy_refcounts",
> +            .type = QEMU_OPT_BOOL,
> +            .help = "Postpone refcount updates",
> +        },
> +        { /* end of list */ }
> +    },
> +};
> +
>  static int qcow2_open(BlockDriverState *bs, QDict *options, int flags)
>  {
>      BDRVQcowState *s = bs->opaque;
>      int len, i, ret = 0;
>      QCowHeader header;
> +    QemuOpts *opts;
> +    Error *local_err = NULL;
>      uint64_t ext_end;
>  
>      ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
> @@ -495,6 +510,28 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags)
>          }
>      }
>  
> +    /* Enable lazy_refcounts according to image and command line options */
> +    opts = qemu_opts_create_nofail(&qcow2_runtime_opts);
> +    qemu_opts_absorb_qdict(opts, options, &local_err);

This breaks migration with qcow2 images:

Program received signal SIGSEGV, Segmentation fault.
qdict_next_entry (first_bucket=0, qdict=0x0) at /home/pbonzini/work/upstream/qemu/qobject/qdict.c:371
371	        if (!QLIST_EMPTY(&qdict->table[i])) {
(gdb) up
#1  qdict_first (qdict=qdict@entry=0x0) at /home/pbonzini/work/upstream/qemu/qobject/qdict.c:384
384	    return qdict_next_entry(qdict, 0);
(gdb) 
#2  0x00007fb8edf75ae6 in qemu_opts_absorb_qdict (opts=opts@entry=0x7fb8f0651740, qdict=qdict@entry=0x0, errp=errp@entry=0x7fb8edc36e80)
    at /home/pbonzini/work/upstream/qemu/util/qemu-option.c:1078
1078	    entry = qdict_first(qdict);
(gdb) 
#3  0x00007fb8edd15074 in qcow2_open (bs=0x7fb8f041b800, options=0x0, flags=<optimized out>) at /home/pbonzini/work/upstream/qemu/block/qcow2.c:515
515	    qemu_opts_absorb_qdict(opts, options, &local_err);
(gdb) 
#4  0x00007fb8edd00352 in bdrv_invalidate_cache (bs=0x7fb8f041b800) at /home/pbonzini/work/upstream/qemu/block.c:4192
4192	        bs->drv->bdrv_invalidate_cache(bs);

Paolo

> +    if (error_is_set(&local_err)) {
> +        qerror_report_err(local_err);
> +        error_free(local_err);
> +        ret = -EINVAL;
> +        goto fail;
> +    }
> +
> +    s->use_lazy_refcounts = qemu_opt_get_bool(opts, "lazy_refcounts",
> +        (s->compatible_features & QCOW2_COMPAT_LAZY_REFCOUNTS));
> +
> +    qemu_opts_del(opts);
> +
> +    if (s->use_lazy_refcounts && s->qcow_version < 3) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR, "Lazy refcounts require "
> +            "a qcow2 image with at least qemu 1.1 compatibility level");
> +        ret = -EINVAL;
> +        goto fail;
> +    }
> +
>  #ifdef DEBUG_ALLOC
>      {
>          BdrvCheckResult result = {0};
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 718b52b..103abdb 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -173,6 +173,7 @@ typedef struct BDRVQcowState {
>  
>      int flags;
>      int qcow_version;
> +    bool use_lazy_refcounts;
>  
>      uint64_t incompatible_features;
>      uint64_t compatible_features;
>