[lttng-dev] [PATCH] Fix: truncate the metadata file in shm-path

[Liguang Li]

Hi Jérémie,

Thanks for your review, i agree with your modification.

Regards,
Liguang

On 11/29/2016 06:00 AM, Jérémie Galarneau wrote:
> Hi Liguang,
>
> Good catch, thanks for the fix!
> I have slightly modified the patch prior to merging it, read on.
>
> Jérémie
>
> On 28 November 2016 at 03:37, Liguang Li <liguang.li at windriver.com> wrote:
>> In the shm-path mode, the metadata will be backuped to a metadata file,
>> when run the lttng command "lttng metadata regenerate" to resample the
>> wall time following a major NTP correction, the metadata file will not
>> be truncated and regenerated.
>>
>> Add the function ust_metadata_truncate() to truncate and regenerate the
>> metadata file.
>>
>> Signed-off-by: Liguang Li <liguang.li at windriver.com>
>> ---
>>   src/bin/lttng-sessiond/cmd.c | 28 ++++++++++++++++++++++++++++
>>   1 file changed, 28 insertions(+)
>>
>> diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
>> index 325ffd2..ba83226 100644
>> --- a/src/bin/lttng-sessiond/cmd.c
>> +++ b/src/bin/lttng-sessiond/cmd.c
>> @@ -3378,6 +3378,25 @@ end:
>>   }
>>
>>   static
>> +int ust_metadata_truncate(int fd, size_t length)
> Changed the name of this function to clear_metadata_file(...) which
> only takes an "fd" as parameter. There are no other users of this
> utility yet, so I'm keeping it specific to its current use.
>
>> +{
>> +       int ret;
>> +
>> +       ret = lseek(fd, length, SEEK_SET);
> length replaced by 0
>
>> +       if (ret < 0) {
>> +               PERROR("lseek");
>> +               goto out;
>> +       }
>> +
>> +       ret = ftruncate(fd, length);
> length replaced by 0
>
>> +       if (ret < 0)
>> +               PERROR("ftruncate");
> We use curly-braces even on single-line conditionals in this codebase.
>
>> +
>> +out:
> Changed the "out" label to "end" to remain consistent with the rest of the code.
>
>> +       return ret;
>> +}
>> +
>> +static
>>   int ust_regenerate_metadata(struct ltt_ust_session *usess)
>>   {
>>          int ret = 0;
>> @@ -3398,6 +3417,15 @@ int ust_regenerate_metadata(struct ltt_ust_session *usess)
>>                  memset(registry->metadata, 0, registry->metadata_alloc_len);
>>                  registry->metadata_len = 0;
>>                  registry->metadata_version++;
>> +               /*truncate the metadata file*/
>> +               if (registry->metadata_fd > 0) {
>> +                       ret = ust_metadata_truncate(registry->metadata_fd, 0);
>> +                       if (ret) {
>> +                               pthread_mutex_unlock(&registry->lock);
>> +                               goto end;
>> +                       }
>> +               }
>> +
>>                  ret = ust_metadata_session_statedump(registry, NULL,
>>                                  registry->major, registry->minor);
>>                  if (ret) {
>> --
>> 2.7.4
>>
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>
>