Re: [Qemu-devel] [PATCH 2/2] qga: add guest-set-time command

[Eric Blake <eblake@redhat.com>]

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On 03/01/2013 02:33 AM, Lei Li wrote:
> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  qga/commands-posix.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qga/qapi-schema.json | 27 ++++++++++++++++++++++++++
>  2 files changed, 82 insertions(+)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index f159e25..e246a0d 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -135,6 +135,61 @@ int64_t qmp_guest_get_time(Error **errp)
>     return time_ns; 
>  }
>  
> +void qmp_guest_set_time(int64_t time_ns, Error **errp)
> +{
> +    int ret;
> +    int status;
> +    pid_t pid;
> +    Error *local_err = NULL;
> +    struct timeval tv;
> +
> +    /* year-2038 will overflow in case time_t is 32bit */
> +    if ((sizeof(time_t) <= 4) && ((unsigned long) time_ns & (1ul << 31))) {

Wrong.  If 'unsigned long' and 'time_t' are both 32 bits, but time_ns is
0x1000000000000000, then the cast truncates to 0 and you don't report
overflow.  Conversely, if time_ns is 0x80000000, you report overflow,
even though this value fits in 32-bit time_t after you do division from
nanoseconds back to seconds.  What you WANT is:

if (time_ns / 1000000000 != (time_t)(time_ns / 1000000000)) {

> +        error_setg_errno(errp, errno, "Invalid time %ld for overflow",
> +                         time_ns);

That wording sounds awkward.  Worse, errno is NOT set to anything sane,
so you do NOT want error_setg_errno.  And %ld is wrong for int64_t on
32-bit platforms.  How about:

error_setg(errp, "Time %" PRI64D " is too large", time_ns);

> +++ b/qga/qapi-schema.json
> @@ -99,6 +99,33 @@
>    'returns': 'int' }
>  
>  ##
> +# @guest-set-time:
> +#
> +# Set guest time.
> +#
> +# Right now, when a guest is paused or migrated to a file

s/Right now, when/When/

> +# then loaded from that file, the guest OS has no idea that
> +# there was a big gap in the time. Depending on how long
> +# the gap was, NTP might not be able to resynchronize the
> +# guest.
> +#
> +# This command tries to set guest time based on the information
> +# from host or an absolute value given by management app, and
> +# set the Hardware Clock to the current System Time. This
> +# will make it easier for a guest to resynchronize without
> +# waiting for NTP.
> +#
> +# @time: time of nanoseconds, relative to the Epoch of
> +#        1970-01-01 in UTC/GMT.

drop '/GMT'

> +#
> +# Returns: Nothing on success.
> +#
> +# Since: 1.5
> +##
> +{ 'command': 'guest-set-time',
> +  'data': { 'time': 'int' } }
> +
> +##
>  # @GuestAgentCommandInfo:
>  #
>  # Information about guest agent commands.
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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