Extend CAS interface with Write-only cache mode

Write-only (WO) cache mode is similar to Write-back (WB), however
read operations do not promote data to cache. Reads are mostly
serviced by the core device, only dirty sectors are fetched from
the cache.

Write-only cache mode is behaving similarly to Write-back with
respect to flushing dirty data. For example it is required to
explicitly enable/disable flushing when changing cache mode
from WO to something other than WB.

Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>

casadm/cas_lib.c

@@ -254,6 +254,7 @@ static struct name_to_val_mapping cache_mode_names[] = {
 #ifdef WI_AVAILABLE
 	{ .short_name = "wi", .long_name = "Write-Invalidate", .value = ocf_cache_mode_wi },
 #endif
+	{ .short_name = "wo", .long_name = "Write-Only", .value = ocf_cache_mode_wo },
 	{ NULL }
 };
 
@@ -1062,6 +1063,7 @@ int set_cache_mode(unsigned int cache_mode, unsigned int cache_id, int flush)
 	int fd = 0;
 	int orig_mode;
 	struct kcas_set_cache_state cmd;
+	bool flush_param_required;
 
 	fd = open_ctrl_device();
 	if (fd == -1)
@@ -1073,9 +1075,13 @@ int set_cache_mode(unsigned int cache_mode, unsigned int cache_id, int flush)
 		return FAILURE;
 	}
 
-	/* if flushing mode is undefined, set it to default (but only if original mode is write back mode) */
+	/* If flushing mode is undefined, set it to default unless we're transitioning
+	 * out of lazy write cache mode (like WB or WO), in which case user must explicitly
+	 * state his preference */
+	flush_param_required = ocf_mngt_cache_mode_has_lazy_write(orig_mode) &&
+			!ocf_mngt_cache_mode_has_lazy_write(cache_mode);
 	if (-1 == flush) {
-		if (ocf_cache_mode_wb == orig_mode) {
+		if (flush_param_required) {
 			cas_printf(LOG_ERR, "Error: Required parameter (‘--flush-cache’) was not specified.\n");
 			close(fd);
 			return FAILURE;
@@ -1084,14 +1090,15 @@ int set_cache_mode(unsigned int cache_mode, unsigned int cache_id, int flush)
 		}
 	}
 
-	if (ocf_cache_mode_wb == orig_mode) {
+	if (flush_param_required) {
 		if (1 == flush) {
 			cas_printf(LOG_INFO, "CAS is currently flushing dirty data to primary storage devices.\n");
 		} else {
-			cas_printf(LOG_INFO, "CAS is currently migrating from Write-Back to %s mode.\n"
+			cas_printf(LOG_INFO, "CAS is currently migrating from %s to %s mode.\n"
 				"Dirty data are being flushed to primary storage device in background.\n"
 				"Please find flushing progress via list caches command (‘casadm -L’) or\n"
 				"via statistics command (‘casadm -P’).\n",
+				cache_mode_to_name_long(orig_mode),
 				cache_mode_to_name_long(cache_mode));
 		}
 	}

casadm/cas_lib.h

@@ -125,15 +125,15 @@ int start_cache(ocf_cache_id_t cache_id, unsigned int cache_init,
 int stop_cache(ocf_cache_id_t cache_id, int flush);
 
 #ifdef WI_AVAILABLE
-#define CAS_CLI_HELP_START_CACHE_MODES "wt|wb|wa|pt|wi"
+#define CAS_CLI_HELP_START_CACHE_MODES "wt|wb|wa|pt|wi|wo"
-#define CAS_CLI_HELP_SET_CACHE_MODES "wt|wb|wa|pt|wi"
+#define CAS_CLI_HELP_SET_CACHE_MODES "wt|wb|wa|pt|wi|wo"
-#define CAS_CLI_HELP_SET_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Invalidate"
+#define CAS_CLI_HELP_SET_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Invalidate, Write-Only"
-#define CAS_CLI_HELP_START_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Invalidate"
+#define CAS_CLI_HELP_START_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Invalidate, Write-Only"
 #else
-#define CAS_CLI_HELP_START_CACHE_MODES "wt|wb|wa|pt"
+#define CAS_CLI_HELP_START_CACHE_MODES "wt|wb|wa|pt|wo"
-#define CAS_CLI_HELP_SET_CACHE_MODES "wt|wb|wa|pt"
+#define CAS_CLI_HELP_SET_CACHE_MODES "wt|wb|wa|pt|wo"
-#define CAS_CLI_HELP_START_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through"
+#define CAS_CLI_HELP_START_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Only"
-#define CAS_CLI_HELP_SET_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through"
+#define CAS_CLI_HELP_SET_CACHE_MODES_FULL "Write-Through, Write-Back, Write-Around, Pass-Through, Write-Only"
 #endif
 
 /**

casadm/cas_main.c

@@ -900,7 +900,7 @@ int handle_get_param()
 static cli_option set_state_cache_mode_options[] = {
 	{'c', "cache-mode", "Cache mode. Available cache modes: {"CAS_CLI_HELP_SET_CACHE_MODES"}", 1, "NAME", CLI_OPTION_REQUIRED},
 	{'i', "cache-id", CACHE_ID_DESC, 1, "ID", CLI_OPTION_REQUIRED},
-	{'f', "flush-cache", "Flush all dirty data from cache before switching to new mode. Option is required when switching from Write-Back mode", 1, "yes|no",0},
+	{'f', "flush-cache", "Flush all dirty data from cache before switching to new mode. Option is required when switching from Write-Back or Write-Only mode", 1, "yes|no",0},
 	{0},
 };
 

casadm/statistics_model.c

@@ -911,9 +911,8 @@ int cache_stats_conf(int ctrl_fd, const struct kcas_cache_info *cache_info,
 		return FAILURE;
 	print_kv_pair(outfile, "Inactive Core Devices", "%d", inactive_cores);
 
-	print_kv_pair(outfile, "Write Policy", "%s%s",
+	print_kv_pair(outfile, "Write Policy", "%s",
-		      (flush_progress && cache_info->info.cache_mode != ocf_cache_mode_wb)
+		      cache_mode_to_name(cache_info->info.cache_mode));
-		      ? "wb->" : "", cache_mode_to_name(cache_info->info.cache_mode));
 	print_kv_pair(outfile, "Eviction Policy", "%s",
 		      eviction_policy_to_name(cache_info->info.eviction_policy));
 	print_kv_pair(outfile, "Cleaning Policy", "%s",

ocf

@@ -1 +1 @@
-Subproject commit 75ec3c7db424e11b6e5fbde5f5afba12b824f849
+Subproject commit aeaeafb639ee20f0320ed859efd4a002810f141d

utils/casadm.8

@@ -62,6 +62,13 @@ to the core device. Pass-Through mode may be used in case if user doesn't want t
 cache any workload, for example in case if there are some maintenance operations
 causing cache pollution.
 
+.TP
+.B Write-Only (wo)
+In Write-Only mode write operations are handled exactly like in Write-Back mode. Read
+operations do not promote data to cache. Reads are typically serviced by the core
+device, unless corresponding cache lines are dirty.
+
+
 .SH COMMANDS
 .TP
 .B -S, --start-cache

utils/opencas.py

@@ -261,7 +261,7 @@ class cas_config(object):
                         format(self.device))
 
         def check_cache_mode_valid(self, cache_mode):
-            if cache_mode.lower() not in ['wt', 'pt', 'wa', 'wb']:
+            if cache_mode.lower() not in ['wt', 'pt', 'wa', 'wb', 'wo']:
                 raise ValueError('Invalid cache mode {0}'.format(cache_mode))
 
         def check_cleaning_policy_valid(self, cleaning_policy):