Add zpool_events_seek() functionality

The ZFS_IOC_EVENTS_SEEK ioctl was added to allow user space callers
to seek around the zevent file descriptor by EID.  When a specific
EID is passed and it exists the cursor will be positioned there.
If the EID is no longer cached by the kernel ENOENT is returned.
The caller may also pass ZEVENT_SEEK_START or ZEVENT_SEEK_END to seek
to those respective locations.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Chris Dunlap <[email protected]>
Issue #2

2 files changed, 85 insertions, 0 deletions

diff --git a/module/zfs/fm.c b/module/zfs/fm.c
index fe9223ff8..246b3d2cf 100644
--- a/module/zfs/fm.c
+++ b/module/zfs/fm.c
@@ -664,6 +664,67 @@ out:
 	return (error);
 }
 
+/*
+ * The caller may seek to a specific EID by passing that EID.  If the EID
+ * is still available in the posted list of events the cursor is positioned
+ * there.  Otherwise ENOENT is returned and the cursor is not moved.
+ *
+ * There are two reserved EIDs which may be passed and will never fail.
+ * ZEVENT_SEEK_START positions the cursor at the start of the list, and
+ * ZEVENT_SEEK_END positions the cursor at the end of the list.
+ */
+int
+zfs_zevent_seek(zfs_zevent_t *ze, uint64_t eid)
+{
+	zevent_t *ev;
+	int error = 0;
+
+	mutex_enter(&zevent_lock);
+
+	if (eid == ZEVENT_SEEK_START) {
+		if (ze->ze_zevent)
+			list_remove(&ze->ze_zevent->ev_ze_list, ze);
+
+		ze->ze_zevent = NULL;
+		goto out;
+	}
+
+	if (eid == ZEVENT_SEEK_END) {
+		if (ze->ze_zevent)
+			list_remove(&ze->ze_zevent->ev_ze_list, ze);
+
+		ev = list_head(&zevent_list);
+		if (ev) {
+			ze->ze_zevent = ev;
+			list_insert_head(&ev->ev_ze_list, ze);
+		} else {
+			ze->ze_zevent = NULL;
+		}
+
+		goto out;
+	}
+
+	for (ev = list_tail(&zevent_list); ev != NULL;
+	    ev = list_prev(&zevent_list, ev)) {
+		if (ev->ev_eid == eid) {
+			if (ze->ze_zevent)
+				list_remove(&ze->ze_zevent->ev_ze_list, ze);
+
+			ze->ze_zevent = ev;
+			list_insert_head(&ev->ev_ze_list, ze);
+			break;
+		}
+	}
+
+	if (ev == NULL)
+		error = ENOENT;
+
+out:
+	mutex_exit(&zevent_lock);
+
+	return (error);
+}
+
 void
 zfs_zevent_init(zfs_zevent_t **zep)
 {
diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 5951bc673..cd4779016 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -4921,6 +4921,28 @@ zfs_ioc_events_clear(zfs_cmd_t *zc)
 
 /*
  * inputs:
+ * zc_guid		eid | ZEVENT_SEEK_START | ZEVENT_SEEK_END
+ * zc_cleanup		zevent file descriptor
+ */
+static int
+zfs_ioc_events_seek(zfs_cmd_t *zc)
+{
+	zfs_zevent_t *ze;
+	minor_t minor;
+	int error;
+
+	error = zfs_zevent_fd_hold(zc->zc_cleanup_fd, &minor, &ze);
+	if (error != 0)
+		return (error);
+
+	error = zfs_zevent_seek(ze, zc->zc_guid);
+	zfs_zevent_fd_rele(zc->zc_cleanup_fd);
+
+	return (error);
+}
+
+/*
+ * inputs:
  * zc_name		name of new filesystem or snapshot
  * zc_value		full name of old snapshot
  *
@@ -5393,6 +5415,8 @@ zfs_ioctl_init(void)
 	    zfs_secpolicy_config, NO_NAME, B_FALSE, POOL_CHECK_NONE);
 	zfs_ioctl_register_legacy(ZFS_IOC_EVENTS_CLEAR, zfs_ioc_events_clear,
 	    zfs_secpolicy_config, NO_NAME, B_FALSE, POOL_CHECK_NONE);
+	zfs_ioctl_register_legacy(ZFS_IOC_EVENTS_SEEK, zfs_ioc_events_seek,
+	    zfs_secpolicy_config, NO_NAME, B_FALSE, POOL_CHECK_NONE);
 }
 
 int