performance/quick-read: provide an invalidation based on ctime

Quick-read by default uses mtime to identify changes to file
data. However there are applications like rsync which explicitly set
mtime making it unreliable for the purpose of identifying change in
file content. Since ctime also changes when content of a file changes
and it cannot be set explicitly, it becomes suitable for identifying
staleness of cached data. This option makes quick-read to prefer ctime
over mtime to validate its cache. However, using ctime can result in
false positives as ctime changes with just attribute changes like
permission without changes to file data. So, use this option only when
mtime is not reliable.

credits to Kotresh Hiremath Ravishankar <khiremat@redhat.com> for
suggestion on using ctime instead of mtime.

Change-Id: Ib3ae39a3252b2876c8ffe81f471d02a87190e9b9
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Updates: bz#1591621

2 files changed, 49 insertions, 1 deletions

diff --git a/xlators/performance/quick-read/src/quick-read.c b/xlators/performance/quick-read/src/quick-read.c
index c3581783365..d26742b0c5e 100644
--- a/xlators/performance/quick-read/src/quick-read.c
+++ b/xlators/performance/quick-read/src/quick-read.c
@@ -334,6 +334,8 @@ qr_content_update (xlator_t *this, qr_inode_t *qr_inode, void *data,
 
 		qr_inode->ia_mtime = buf->ia_mtime;
 		qr_inode->ia_mtime_nsec = buf->ia_mtime_nsec;
+                qr_inode->ia_ctime = buf->ia_ctime;
+                qr_inode->ia_ctime_nsec = buf->ia_ctime_nsec;
 
 		qr_inode->buf = *buf;
 
@@ -363,6 +365,24 @@ qr_mtime_equal (qr_inode_t *qr_inode, struct iatt *buf)
 }
 
 
+gf_boolean_t
+qr_ctime_equal (qr_inode_t *qr_inode, struct iatt *buf)
+{
+        return (qr_inode->ia_ctime == buf->ia_ctime &&
+                qr_inode->ia_ctime_nsec == buf->ia_ctime_nsec);
+}
+
+
+gf_boolean_t
+qr_time_equal (qr_conf_t *conf, qr_inode_t *qr_inode, struct iatt *buf)
+{
+        if (conf->ctime_invalidation)
+                return qr_ctime_equal (qr_inode, buf);
+        else
+                return qr_mtime_equal (qr_inode, buf);
+}
+
+
 void
 __qr_content_refresh (xlator_t *this, qr_inode_t *qr_inode, struct iatt *buf,
                       uint64_t gen)
@@ -381,7 +401,7 @@ __qr_content_refresh (xlator_t *this, qr_inode_t *qr_inode, struct iatt *buf,
 
         qr_inode->gen = gen;
 
-	if (qr_size_fits (conf, buf) && qr_mtime_equal (qr_inode, buf)) {
+	if (qr_size_fits (conf, buf) && qr_time_equal (conf, qr_inode, buf)) {
 		qr_inode->buf = *buf;
 
 		gettimeofday (&qr_inode->last_refresh, NULL);
@@ -981,6 +1001,9 @@ qr_reconfigure (xlator_t *this, dict_t *options)
         GF_OPTION_RECONF ("cache-invalidation", conf->qr_invalidation, options,
                           bool, out);
 
+        GF_OPTION_RECONF ("ctime-invalidation", conf->ctime_invalidation,
+                          options, bool, out);
+
         GF_OPTION_RECONF ("cache-size", cache_size_new, options, size_uint64, out);
         if (!check_cache_size_ok (this, cache_size_new)) {
                 ret = -1;
@@ -1136,6 +1159,9 @@ qr_init (xlator_t *this)
                 goto out;
         }
 
+        GF_OPTION_INIT ("ctime-invalidation", conf->ctime_invalidation, bool,
+                        out);
+
         INIT_LIST_HEAD (&conf->priority_list);
         conf->max_pri = 1;
         if (dict_get (this->options, "priority")) {
@@ -1383,6 +1409,25 @@ struct volume_options qr_options[] = {
           .description = "When \"on\", invalidates/updates the metadata cache,"
                          " on receiving the cache-invalidation notifications",
         },
+        { .key           = {"ctime-invalidation"},
+          .type          = GF_OPTION_TYPE_BOOL,
+          .default_value = "false",
+          .op_version    = {GD_OP_VERSION_4_2_0},
+          .flags         = OPT_FLAG_CLIENT_OPT | OPT_FLAG_SETTABLE | OPT_FLAG_DOC,
+          .description   = "Quick-read by default uses mtime to identify changes "
+                         "to file data. However there are applications like "
+                         "rsync which explicitly set mtime making it unreliable "
+                         "for the purpose of identifying change in file content "
+                         ". Since ctime also changes when content of a file "
+                         " changes and it cannot be set explicitly, it becomes "
+                         " suitable for identifying staleness of cached data. "
+                         "This option makes quick-read to prefer ctime over "
+                         "mtime to validate its cache. However, using ctime "
+                         "can result in false positives as ctime changes with "
+                         "just attribute changes like permission without "
+                         "changes to file data. So, use this only when mtime "
+                         "is not reliable",
+        },
         { .key  = {NULL} }
 };
 
diff --git a/xlators/performance/quick-read/src/quick-read.h b/xlators/performance/quick-read/src/quick-read.h
index cdbf3dfbd63..8ef0f9802b8 100644
--- a/xlators/performance/quick-read/src/quick-read.h
+++ b/xlators/performance/quick-read/src/quick-read.h
@@ -36,6 +36,8 @@ struct qr_inode {
         int               priority;
 	uint32_t          ia_mtime;
 	uint32_t          ia_mtime_nsec;
+        uint32_t          ia_ctime;
+	uint32_t          ia_ctime_nsec;
 	struct iatt       buf;
         struct timeval    last_refresh;
         struct list_head  lru;
@@ -57,6 +59,7 @@ struct qr_conf {
         uint64_t         cache_size;
         int              max_pri;
         gf_boolean_t     qr_invalidation;
+        gf_boolean_t     ctime_invalidation;
         struct list_head priority_list;
 };
 typedef struct qr_conf qr_conf_t;