Re: [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...@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...@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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