[Qemu-devel] [PATCH 0/2 v3] Time resync support by qemu-ga

[Qemu-devel] [PATCH 0/2 v3] Time resync support by qemu-ga

[Lei Li]

This patch series attempts to add time resync support
to qemu-ga by introducing qemu-ga commands guest-get-time
and guest-set-time.

Right now, when a guest is paused or migrated to a file
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.
So adding new guest-agent command that is called any time
a guest is resumed  and which tells the guest to update its
own wall clock time based on the information from the host
will make it easier for a guest to resynchronize without
waiting for NTP.

The previous RFC send for discussion and suggestion as link
here:

http://article.gmane.org/gmane.comp.emulators.qemu/186126

The interface for these commands like:

{ 'command': 'guest-get-time', 'returns': 'int' }

{ 'command': 'guest-set-time', 'data': { 'time': int } }

Notes:
For the implementition of win32-specific commands, I plan
to send it out in another thread later.

Suggestions and comments are welcome!


Changes since v2:
  - Get rid of utc-offset, and make it just pass single nanoseconds
    relative to the Epoch in UTC/GMT according to Anthony and
    Eric's comments.
  - Make time argument mandatory.
  - Fix the overflow check for year-2038 problem.
  - Error handel improvment from Eric. 

Changes since v1:
  - Squashed patches add support to get host time and add
    guest-get-time command into one.
  - Documents improvment based on the suggestions from
    Eric and Mike.
  - Change the name of 'HostTimeInfo' to 'TimeInfo'.
  - Better use-case and logic for 'guest-set-time'
    command suggested by Eric.
  - Error handel improvment from Luiz.

Lei Li (2):
  qga: add guest-get-time command
  qga: add guest-set-time command

[Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Lei Li]

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 qga/commands-posix.c | 16 ++++++++++++++++
 qga/qapi-schema.json | 16 ++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 0ad73f3..f159e25 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
     /* succeded */
 }
 
+int64_t qmp_guest_get_time(Error **errp)
+{
+   int ret;
+   qemu_timeval tq;
+   int64_t time_ns;
+
+   ret = qemu_gettimeofday(&tq);
+   if (ret < 0) {
+       error_setg_errno(errp, errno, "Failed to get time");
+       return -1;
+   }
+
+   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;
+   return time_ns; 
+}
+
 typedef struct GuestFileHandle {
     uint64_t id;
     FILE *fh;
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index d91d903..563600c 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -83,6 +83,22 @@
 { 'command': 'guest-ping' }
 
 ##
+# @guest-get-time:
+#
+# Get the information about guest time relative to the Epoch
+# of 1970-01-01 in UTC/GMT.
+#
+# This command try to get the guest's notion of the current
+# time.
+#
+# Returns: Time in nanoseconds on success.
+#
+# Since 1.5
+##
+{ 'command': 'guest-get-time',
+  'returns': 'int' }
+
+##
 # @GuestAgentCommandInfo:
 #
 # Information about guest agent commands.
-- 
1.7.11.7

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

[Lei Li]

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))) {
+        error_setg_errno(errp, errno, "Invalid time %ld for overflow",
+                         time_ns);
+    }
+
+    tv.tv_sec = time_ns / 1000000000;
+    tv.tv_usec = (time_ns % 1000000000) / 1000;
+
+    ret = settimeofday(&tv, NULL);
+    if (ret < 0) {
+        error_setg_errno(errp, errno, "Failed to set time to guest");
+        return;
+    }
+
+    /* Set the Hardware Clock to the current System Time. */
+    pid = fork();
+    if (pid == 0) {
+        setsid();
+        reopen_fd_to_null(0);
+        reopen_fd_to_null(1);
+        reopen_fd_to_null(2);
+
+        execle("/sbin/hwclock", "hwclock", "-w", NULL, environ);
+        _exit(EXIT_FAILURE);
+    } else if (pid < 0) {
+        error_setg_errno(errp, errno, "failed to create child process");
+        return;
+    }
+
+    ga_wait_child(pid, &status, &local_err);
+    if (error_is_set(&local_err)) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (!WIFEXITED(status)) {
+        error_setg(errp, "child process has terminated abnormally");
+        return;
+    }
+
+    if (WEXITSTATUS(status)) {
+        error_setg(errp, "hwclock failed to set hardware clock to system time");
+        return;
+    }
+}
+
 typedef struct GuestFileHandle {
     uint64_t id;
     FILE *fh;
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index 563600c..5eba324 100644
--- a/qga/qapi-schema.json
+++ 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
+# 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.
+#
+# Returns: Nothing on success.
+#
+# Since: 1.5
+##
+{ 'command': 'guest-set-time',
+  'data': { 'time': 'int' } }
+
+##
 # @GuestAgentCommandInfo:
 #
 # Information about guest agent commands.
-- 
1.7.11.7

Re: [Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Eric Blake]

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On 03/01/2013 02:32 AM, Lei Li wrote:
> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  qga/commands-posix.c | 16 ++++++++++++++++
>  qga/qapi-schema.json | 16 ++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 0ad73f3..f159e25 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
>      /* succeded */
>  }
>  
> +int64_t qmp_guest_get_time(Error **errp)
> +{
> +   int ret;
> +   qemu_timeval tq;
> +   int64_t time_ns;
> +
> +   ret = qemu_gettimeofday(&tq);
> +   if (ret < 0) {
> +       error_setg_errno(errp, errno, "Failed to get time");
> +       return -1;
> +   }
> +
> +   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;

Is it worth a sanity check that the tv_sec scaling doesn't overflow?  Of
course, that won't happen until far into the future (well beyond the
2038 overflow of 32-bit seconds since Epoch), so it won't hit in OUR
lifetime, so I can look the other way.

>  
>  ##
> +# @guest-get-time:
> +#
> +# Get the information about guest time relative to the Epoch
> +# of 1970-01-01 in UTC/GMT.

UTC and GMT are not the same thing.  I'd drop the '/GMT'.
http://www.diffen.com/difference/GMT_vs_UTC

> +#
> +# This command try to get the guest's notion of the current
> +# time.

This sentence is redundant with the first one, and has grammar issues.
Drop it.

> +#
> +# Returns: Time in nanoseconds on success.
> +#
> +# Since 1.5
> +##
> +{ 'command': 'guest-get-time',
> +  'returns': '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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Re: [Qemu-devel] [PATCH 2/2] qga: add guest-set-time command

[Eric Blake]

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

[Eric Blake]

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On 03/01/2013 10:38 AM, Eric Blake wrote:
>> +        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);

Don't know what I was thinking; there is no PRI64D.  I meant PRId64.

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


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Re: [Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Lei Li]

On 03/02/2013 01:02 AM, Eric Blake wrote:
> On 03/01/2013 02:32 AM, Lei Li wrote:
>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>> ---
>>   qga/commands-posix.c | 16 ++++++++++++++++
>>   qga/qapi-schema.json | 16 ++++++++++++++++
>>   2 files changed, 32 insertions(+)
>>
>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
>> index 0ad73f3..f159e25 100644
>> --- a/qga/commands-posix.c
>> +++ b/qga/commands-posix.c
>> @@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
>>       /* succeded */
>>   }
>>   
>> +int64_t qmp_guest_get_time(Error **errp)
>> +{
>> +   int ret;
>> +   qemu_timeval tq;
>> +   int64_t time_ns;
>> +
>> +   ret = qemu_gettimeofday(&tq);
>> +   if (ret < 0) {
>> +       error_setg_errno(errp, errno, "Failed to get time");
>> +       return -1;
>> +   }
>> +
>> +   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;
> Is it worth a sanity check that the tv_sec scaling doesn't overflow?  Of
> course, that won't happen until far into the future (well beyond the
> 2038 overflow of 32-bit seconds since Epoch), so it won't hit in OUR
> lifetime, so I can look the other way.
>>   
>>   ##
>> +# @guest-get-time:
>> +#
>> +# Get the information about guest time relative to the Epoch
>> +# of 1970-01-01 in UTC/GMT.
> UTC and GMT are not the same thing.  I'd drop the '/GMT'.
> http://www.diffen.com/difference/GMT_vs_UTC

Oh, good to know! :)
Thanks.

>> +#
>> +# This command try to get the guest's notion of the current
>> +# time.
> This sentence is redundant with the first one, and has grammar issues.
> Drop it.

Sure.

>
>> +#
>> +# Returns: Time in nanoseconds on success.
>> +#
>> +# Since 1.5
>> +##
>> +{ 'command': 'guest-get-time',
>> +  'returns': 'int' }
>> +
>> +##
>>   # @GuestAgentCommandInfo:
>>   #
>>   # Information about guest agent commands.
>>


-- 
Lei

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

[Lei Li]

On 03/02/2013 01:38 AM, Eric Blake wrote:
> 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:

Yes, you are right.. thanks.

>
> 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);

Sure, will address it as the your later reply.

>> +++ 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.
>>


-- 
Lei

[Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Lei Li]

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 qga/commands-posix.c | 16 ++++++++++++++++
 qga/qapi-schema.json | 13 +++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 0ad73f3..6fc6003 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
     /* succeded */
 }
 
+int64_t qmp_guest_get_time(Error **errp)
+{
+   int ret;
+   qemu_timeval tq;
+   int64_t time_ns;
+
+   ret = qemu_gettimeofday(&tq);
+   if (ret < 0) {
+       error_setg_errno(errp, errno, "Failed to get time");
+       return -1;
+   }
+
+   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;
+   return time_ns;
+}
+
 typedef struct GuestFileHandle {
     uint64_t id;
     FILE *fh;
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index d91d903..52bb091 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -83,6 +83,19 @@
 { 'command': 'guest-ping' }
 
 ##
+# @guest-get-time:
+#
+# Get the information about guest time relative to the Epoch
+# of 1970-01-01 in UTC.
+#
+# Returns: Time in nanoseconds on success.
+#
+# Since 1.5
+##
+{ 'command': 'guest-get-time',
+  'returns': 'int' }
+
+##
 # @GuestAgentCommandInfo:
 #
 # Information about guest agent commands.
-- 
1.7.11.7

Re: [Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[mdroth]

On Mon, Mar 04, 2013 at 05:16:29PM +0800, Lei Li wrote:
> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>

> ---
>  qga/commands-posix.c | 16 ++++++++++++++++
>  qga/qapi-schema.json | 13 +++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 0ad73f3..6fc6003 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
>      /* succeded */
>  }
> 
> +int64_t qmp_guest_get_time(Error **errp)
> +{
> +   int ret;
> +   qemu_timeval tq;
> +   int64_t time_ns;
> +
> +   ret = qemu_gettimeofday(&tq);
> +   if (ret < 0) {
> +       error_setg_errno(errp, errno, "Failed to get time");
> +       return -1;
> +   }
> +
> +   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;
> +   return time_ns;
> +}
> +
>  typedef struct GuestFileHandle {
>      uint64_t id;
>      FILE *fh;
> diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
> index d91d903..52bb091 100644
> --- a/qga/qapi-schema.json
> +++ b/qga/qapi-schema.json
> @@ -83,6 +83,19 @@
>  { 'command': 'guest-ping' }
> 
>  ##
> +# @guest-get-time:
> +#
> +# Get the information about guest time relative to the Epoch
> +# of 1970-01-01 in UTC.
> +#
> +# Returns: Time in nanoseconds on success.
> +#
> +# Since 1.5
> +##
> +{ 'command': 'guest-get-time',
> +  'returns': 'int' }
> +
> +##
>  # @GuestAgentCommandInfo:
>  #
>  # Information about guest agent commands.
> -- 
> 1.7.11.7
> 

Re: [Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Eric Blake]

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On 03/04/2013 02:16 AM, Lei Li wrote:
> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  qga/commands-posix.c | 16 ++++++++++++++++
>  qga/qapi-schema.json | 13 +++++++++++++
>  2 files changed, 29 insertions(+)
> 

>  ##
> +# @guest-get-time:
> +#
> +# Get the information about guest time relative to the Epoch
> +# of 1970-01-01 in UTC.
> +#
> +# Returns: Time in nanoseconds on success.

The return value is only possible on success in the first place, so you
can simplify this:

s/ on success//

But that's minor, and I'm okay even with the longer wording, so:

Reviewed-by: Eric Blake <eblake@redhat.com>

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


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[Qemu-devel] [PATCH 1/2] qga: add guest-get-time command

[Lei Li]

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 qga/commands-posix.c | 16 ++++++++++++++++
 qga/qapi-schema.json | 13 +++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 7a0202e..1426262 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -119,6 +119,22 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
     /* succeded */
 }
 
+int64_t qmp_guest_get_time(Error **errp)
+{
+   int ret;
+   qemu_timeval tq;
+   int64_t time_ns;
+
+   ret = qemu_gettimeofday(&tq);
+   if (ret < 0) {
+       error_setg_errno(errp, errno, "Failed to get time");
+       return -1;
+   }
+
+   time_ns = tq.tv_sec * 1000000000LL + tq.tv_usec * 1000;
+   return time_ns;
+}
+
 typedef struct GuestFileHandle {
     uint64_t id;
     FILE *fh;
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index d91d903..bb0f75e 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -83,6 +83,19 @@
 { 'command': 'guest-ping' }
 
 ##
+# @guest-get-time:
+#
+# Get the information about guest time relative to the Epoch
+# of 1970-01-01 in UTC.
+#
+# Returns: Time in nanoseconds.
+#
+# Since 1.5
+##
+{ 'command': 'guest-get-time',
+  'returns': 'int' }
+
+##
 # @GuestAgentCommandInfo:
 #
 # Information about guest agent commands.
-- 
1.7.11.7