LU-14663 mdc: start changelog thread upon first access

thus leaving the caller a chance to set CHANGELOG_FLAG_FOLLOW,
otherwise the thread (started from open()) can reach the end
of the changelog and exit early.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ic14b6c991010bbe5197b5a8b0fedf0f4007e98c1
Reviewed-on: https://review.whamcloud.com/43513
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/mdc/mdc_changelog.c b/lustre/mdc/mdc_changelog.c
index 459f4f0..843c4de 100644 (file)
--- a/lustre/mdc/mdc_changelog.c
+++ b/lustre/mdc/mdc_changelog.c
@@ -364,6 +364,33 @@ err_out:
        RETURN(rc);
 }
 
        RETURN(rc);
 }
 

+static int chlg_start_thread(struct file *file)
+{
+       struct chlg_reader_state *crs = file->private_data;
+       struct task_struct *task;
+       int rc = 0;
+
+       if (likely(crs->crs_prod_task))
+               return 0;
+       if (unlikely(file->f_mode & FMODE_READ) == 0)
+               return 0;
+
+       mutex_lock(&crs->crs_lock);
+       if (crs->crs_prod_task == NULL) {
+               task = kthread_run(chlg_load, crs, "chlg_load_thread");
+               if (IS_ERR(task)) {
+                       rc = PTR_ERR(task);
+                       CERROR("%s: cannot start changelog thread: rc = %d\n",
+                              crs->crs_ced->ced_name, rc);
+                       GOTO(out, rc);
+               }
+               crs->crs_prod_task = task;
+       }
+out:
+       mutex_unlock(&crs->crs_lock);
+       return rc;
+}
+

 /**
  * Read handler, dequeues records from the chlg_reader_state if any.
  * No partial records are copied to userland so this function can return less
 /**
  * Read handler, dequeues records from the chlg_reader_state if any.
  * No partial records are copied to userland so this function can return less


@@ -396,6 +423,10 @@ static ssize_t chlg_read(struct file *file, char __user *buff, size_t count,
                        RETURN(-EAGAIN);
        }
 
                        RETURN(-EAGAIN);
        }
 

+       rc = chlg_start_thread(file);
+       if (rc)
+               RETURN(rc);
+

        rc = wait_event_interruptible(crs->crs_waitq_cons,
                        crs->crs_rec_count > 0 || crs->crs_eof || crs->crs_err);
 
        rc = wait_event_interruptible(crs->crs_waitq_cons,
                        crs->crs_rec_count > 0 || crs->crs_eof || crs->crs_err);
 


@@ -592,8 +623,6 @@ static int chlg_open(struct inode *inode, struct file *file)
 {
        struct chlg_reader_state *crs;
        struct chlg_registered_dev *dev;
 {
        struct chlg_reader_state *crs;
        struct chlg_registered_dev *dev;

-       struct task_struct *task;
-       int rc;

        ENTRY;
 
        dev = container_of(inode->i_cdev, struct chlg_registered_dev, ced_cdev);
        ENTRY;
 
        dev = container_of(inode->i_cdev, struct chlg_registered_dev, ced_cdev);


@@ -611,25 +640,10 @@ static int chlg_open(struct inode *inode, struct file *file)
        INIT_LIST_HEAD(&crs->crs_rec_queue);
        init_waitqueue_head(&crs->crs_waitq_prod);
        init_waitqueue_head(&crs->crs_waitq_cons);
        INIT_LIST_HEAD(&crs->crs_rec_queue);
        init_waitqueue_head(&crs->crs_waitq_prod);
        init_waitqueue_head(&crs->crs_waitq_cons);

-
-       if (file->f_mode & FMODE_READ) {
-               task = kthread_run(chlg_load, crs, "chlg_load_thread");
-               if (IS_ERR(task)) {
-                       rc = PTR_ERR(task);
-                       CERROR("%s: cannot start changelog thread: rc = %d\n",
-                              dev->ced_name, rc);
-                       GOTO(err_crs, rc);
-               }
-               crs->crs_prod_task = task;
-       }
+       crs->crs_prod_task = NULL;

 
        file->private_data = crs;
        RETURN(0);
 
        file->private_data = crs;
        RETURN(0);

-
-err_crs:
-       kref_put(&dev->ced_refs, chlg_dev_clear);
-       OBD_FREE_PTR(crs);
-       return rc;

 }
 
 /**
 }
 
 /**


@@ -670,6 +684,11 @@ static unsigned int chlg_poll(struct file *file, poll_table *wait)
 {
        struct chlg_reader_state *crs = file->private_data;
        unsigned int mask = 0;
 {
        struct chlg_reader_state *crs = file->private_data;
        unsigned int mask = 0;

+       int rc;
+
+       rc = chlg_start_thread(file);
+       if (rc)
+               RETURN(rc);

 
        mutex_lock(&crs->crs_lock);
        poll_wait(file, &crs->crs_waitq_cons, wait);
 
        mutex_lock(&crs->crs_lock);
        poll_wait(file, &crs->crs_waitq_cons, wait);