scsi: zfcp: move maximum age of diagnostic buffers into a per-adapter variable

Replace the static define (ZFCP_DIAG_MAX_AGE) with a per-adapter variable
(${adapter}->diagnostics->max_age). This new variable is exported via
sysfs, along with other, already existing adapter variables, and can both
be read and written. This way users can choose how much time should pass
between refreshes of diagnostic buffers. The default value for the age
remains to be five seconds.

By setting this new variable to 0, the caching of diagnostic buffers for
userspace accesses can also be completely removed.

All diagnostic buffers of a given adapter are subject to this setting in
the same way.

Link: https://lore.kernel.org/r/b1d0977cc884b16dd4ca6418e4320c56a4c31d63.1572018132.git.bblock@linux.ibm.comReviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_diag.c

@@ -19,9 +19,6 @@
 #include "zfcp_ext.h"
 #include "zfcp_def.h"
 
-/* Max age of data in a diagnostics buffer before it needs a refresh (in ms). */
-#define ZFCP_DIAG_MAX_AGE (5 * 1000)
-
 static DECLARE_WAIT_QUEUE_HEAD(__zfcp_diag_publish_wait);
 
 /**
@@ -38,9 +35,6 @@ static DECLARE_WAIT_QUEUE_HEAD(__zfcp_diag_publish_wait);
  */
 int zfcp_diag_adapter_setup(struct zfcp_adapter *const adapter)
 {
-	/* set the timestamp so that the first test on age will always fail */
-	const unsigned long initial_timestamp =
-		jiffies - msecs_to_jiffies(ZFCP_DIAG_MAX_AGE);
 	struct zfcp_diag_adapter *diag;
 	struct zfcp_diag_header *hdr;
 
@@ -48,13 +42,16 @@ int zfcp_diag_adapter_setup(struct zfcp_adapter *const adapter)
 	if (diag == NULL)
 		return -ENOMEM;
 
+	diag->max_age = (5 * 1000); /* default value: 5 s */
+
 	/* setup header for port_data */
 	hdr = &diag->port_data.header;
 
 	spin_lock_init(&hdr->access_lock);
 	hdr->buffer = &diag->port_data.data;
 	hdr->buffer_size = sizeof(diag->port_data.data);
-	hdr->timestamp = initial_timestamp;
+	/* set the timestamp so that the first test on age will always fail */
+	hdr->timestamp = jiffies - msecs_to_jiffies(diag->max_age);
 
 	/* setup header for config_data */
 	hdr = &diag->config_data.header;
@@ -62,7 +59,8 @@ int zfcp_diag_adapter_setup(struct zfcp_adapter *const adapter)
 	spin_lock_init(&hdr->access_lock);
 	hdr->buffer = &diag->config_data.data;
 	hdr->buffer_size = sizeof(diag->config_data.data);
-	hdr->timestamp = initial_timestamp;
+	/* set the timestamp so that the first test on age will always fail */
+	hdr->timestamp = jiffies - msecs_to_jiffies(diag->max_age);
 
 	adapter->diagnostics = diag;
 	return 0;
@@ -240,7 +238,8 @@ static int __zfcp_diag_update_buffer(struct zfcp_adapter *const adapter,
 }
 
 static bool
-__zfcp_diag_test_buffer_age_isfresh(const struct zfcp_diag_header *const hdr)
+__zfcp_diag_test_buffer_age_isfresh(const struct zfcp_diag_adapter *const diag,
+				    const struct zfcp_diag_header *const hdr)
 	__must_hold(hdr->access_lock)
 {
 	const unsigned long now = jiffies;
@@ -252,7 +251,7 @@ __zfcp_diag_test_buffer_age_isfresh(const struct zfcp_diag_header *const hdr)
 	if (!time_after_eq(now, hdr->timestamp))
 		return false;
 
-	if (jiffies_to_msecs(now - hdr->timestamp) >= ZFCP_DIAG_MAX_AGE)
+	if (jiffies_to_msecs(now - hdr->timestamp) >= diag->max_age)
 		return false;
 
 	return true;
@@ -291,7 +290,9 @@ int zfcp_diag_update_buffer_limited(struct zfcp_adapter *const adapter,
 
 	spin_lock_irqsave(&hdr->access_lock, flags);
 
-	for (rc = 0; !__zfcp_diag_test_buffer_age_isfresh(hdr); rc = 0) {
+	for (rc = 0;
+	     !__zfcp_diag_test_buffer_age_isfresh(adapter->diagnostics, hdr);
+	     rc = 0) {
 		rc = __zfcp_diag_update_buffer(adapter, hdr, buffer_update,
 					       &flags);
 		if (rc != -EAGAIN)

drivers/s390/scsi/zfcp_diag.h

@@ -42,6 +42,8 @@ struct zfcp_diag_header {
  *			      adapter.
  * @sysfs_established: flag showing that the associated sysfs-group was created
  *		       during run of zfcp_adapter_enqueue().
+ * @max_age: maximum age of data in diagnostic buffers before they need to be
+ *	     refreshed (in ms).
  * @port_data: data retrieved using exchange port data.
  * @port_data.header: header with metadata for the cache in @port_data.data.
  * @port_data.data: cached QTCB Bottom of command exchange port data.
@@ -52,6 +54,8 @@ struct zfcp_diag_header {
 struct zfcp_diag_adapter {
 	u64	sysfs_established	:1;
 
+	unsigned long	max_age;
+
 	struct {
 		struct zfcp_diag_header		header;
 		struct fsf_qtcb_bottom_port	data;

drivers/s390/scsi/zfcp_sysfs.c

@@ -326,6 +326,50 @@ static ssize_t zfcp_sysfs_port_remove_store(struct device *dev,
 static ZFCP_DEV_ATTR(adapter, port_remove, S_IWUSR, NULL,
 		     zfcp_sysfs_port_remove_store);
 
+static ssize_t
+zfcp_sysfs_adapter_diag_max_age_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct zfcp_adapter *adapter = zfcp_ccw_adapter_by_cdev(to_ccwdev(dev));
+	ssize_t rc;
+
+	if (!adapter)
+		return -ENODEV;
+
+	/* ceil(log(2^64 - 1) / log(10)) = 20 */
+	rc = scnprintf(buf, 20 + 2, "%lu\n", adapter->diagnostics->max_age);
+
+	zfcp_ccw_adapter_put(adapter);
+	return rc;
+}
+
+static ssize_t
+zfcp_sysfs_adapter_diag_max_age_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct zfcp_adapter *adapter = zfcp_ccw_adapter_by_cdev(to_ccwdev(dev));
+	unsigned long max_age;
+	ssize_t rc;
+
+	if (!adapter)
+		return -ENODEV;
+
+	rc = kstrtoul(buf, 10, &max_age);
+	if (rc != 0)
+		goto out;
+
+	adapter->diagnostics->max_age = max_age;
+
+	rc = count;
+out:
+	zfcp_ccw_adapter_put(adapter);
+	return rc;
+}
+static ZFCP_DEV_ATTR(adapter, diag_max_age, 0644,
+		     zfcp_sysfs_adapter_diag_max_age_show,
+		     zfcp_sysfs_adapter_diag_max_age_store);
+
 static struct attribute *zfcp_adapter_attrs[] = {
 	&dev_attr_adapter_failed.attr,
 	&dev_attr_adapter_in_recovery.attr,
@@ -338,6 +382,7 @@ static struct attribute *zfcp_adapter_attrs[] = {
 	&dev_attr_adapter_lic_version.attr,
 	&dev_attr_adapter_status.attr,
 	&dev_attr_adapter_hardware_version.attr,
+	&dev_attr_adapter_diag_max_age.attr,
 	NULL
 };