Re: [Qemu-devel] [PATCH 12/34] hmp: hmp_cont(): don't rely on QERR_DEVICE_ENCRYPTED

[Markus Armbruster]

Luiz Capitulino <address@hidden> writes:

> This commit changes hmp_cont() to loop through all block devices
> and proactively set an encryption key for any encrypted device
> without a valid one.
>
> This change is needed because QERR_DEVICE_ENCRYPTED is going to be
> dropped by a future commit.
>
> Signed-off-by: Luiz Capitulino <address@hidden>
> ---
>  hmp.c | 43 +++++++++++++++++++++++++------------------
>  1 file changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/hmp.c b/hmp.c
> index 6b72a64..1ebeb63 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -610,34 +610,41 @@ void hmp_pmemsave(Monitor *mon, const QDict *qdict)
>  
>  static void hmp_cont_cb(void *opaque, int err)
>  {
> -    Monitor *mon = opaque;
> -
>      if (!err) {
> -        hmp_cont(mon, NULL);
> +        qmp_cont(NULL);
>      }
>  }
>  
> -void hmp_cont(Monitor *mon, const QDict *qdict)
> +static bool blockinfo_is_encrypted(const BlockInfo *bdev)
>  {
> -    Error *errp = NULL;
> -
> -    qmp_cont(&errp);
> -    if (error_is_set(&errp)) {
> -        if (error_is_type(errp, QERR_DEVICE_ENCRYPTED)) {
> -            const char *device;
> +    return (bdev->inserted && bdev->inserted->encrypted);
> +}
>  
> -            /* The device is encrypted. Ask the user for the password
> -               and retry */
> +static bool blockinfo_key_is_set(const BlockInfo *bdev)
> +{
> +    return (bdev->inserted && bdev->inserted->valid_encryption_key);
> +}
>  
> -            device = error_get_field(errp, "device");
> -            assert(device != NULL);
> +void hmp_cont(Monitor *mon, const QDict *qdict)
> +{
> +    BlockInfoList *bdev_list, *bdev;
> +    Error *errp = NULL;
>  
> -            monitor_read_block_device_key(mon, device, hmp_cont_cb, mon);
> -            error_free(errp);
> -            return;
> +    bdev_list = qmp_query_block(NULL);
> +    for (bdev = bdev_list; bdev; bdev = bdev->next) {
> +        if (blockinfo_is_encrypted(bdev->value) &&
> +            !blockinfo_key_is_set(bdev->value)) {
> +                monitor_read_block_device_key(mon, bdev->value->device,
> +                                              hmp_cont_cb, NULL);
> +                goto out;
>          }
> -        hmp_handle_error(mon, &errp);
>      }
> +
> +    qmp_cont(&errp);
> +    hmp_handle_error(mon, &errp);
> +
> +out:
> +    qapi_free_BlockInfoList(bdev_list);
>  }
>  
>  void hmp_system_wakeup(Monitor *mon, const QDict *qdict)

Quote my previous analysis:

Diff makes this change look worse than it is.  Odd: M-x ediff gets it
right.  Anyway, here's how I think it works:

Unchanged qmp_cont(): search the bdrv_states for the first encrypted one
without a key.  If found, set err argument to QERR_DEVICE_ENCRYPTED.
Other errors unrelated to encrypted devices are also possible.

hmp_cont() before: try qmp_cont().  If we get QERR_DEVICE_ENCRYPTED,
extract the device from the error object, and prompt for its key, with a
callback that retries hmp_cont() if the key was provided.

After: search the bdrv_states for an encrypted one without a key.  If
there is none, qmp_cont(), no special error handling.  If there is one,
prompt for its key, with a callback that runs qmp_cont() if the key was
provided.

End quote.

Two observations:

1. I don't understand how this works for multiple encrypted BDSs without
keys.  If there are any, hmp_cont() starts reading the first one's key,
then returns.  But the callback doesn't start reading the next one's
key.  Please explain.

2. qmp_cont() uses bdrv_key_required() to test whether a BDS lacks a
key.  Your new hmp_cont() uses blockinfo_is_encrypted() &&
!blockinfo_key_is_set().  Not obvious that the two are equivalent.

I'm afraid they are not.  bdrv_key_required() checks the backing image
first:

    int bdrv_key_required(BlockDriverState *bs)
    {
        BlockDriverState *backing_hd = bs->backing_hd;

        if (backing_hd && backing_hd->encrypted && !backing_hd->valid_key)
            return 1;
        return (bs->encrypted && !bs->valid_key);
    }

Your code doesn't:

    static bool blockinfo_is_encrypted(const BlockInfo *bdev)
    {
        return (bdev->inserted && bdev->inserted->encrypted);
    }

    static bool blockinfo_key_is_set(const BlockInfo *bdev)
    {
        return (bdev->inserted && bdev->inserted->valid_encryption_key);
    }

    BlockInfoList *qmp_query_block(Error **errp)
    {
        BlockInfoList *head = NULL, *cur_item = NULL;
        BlockDriverState *bs;

        QTAILQ_FOREACH(bs, &bdrv_states, list) {
            BlockInfoList *info = g_malloc0(sizeof(*info));
[...]
            if (bs->drv) {
                info->value->has_inserted = true;
                info->value->inserted = 
g_malloc0(sizeof(*info->value->inserted));
[...]
                info->value->inserted->encrypted = bs->encrypted;
                info->value->inserted->valid_encryption_key = bs->valid_key;
[...]

Are you sure this is correct?

I understand we require HMP code to go via QMP for everything, to keep
HMP honest.  This case shows a drawback: duplicated code, leading to
inconsistencies.