dm log userspace: add log device dependency

Allow userspace dm log implementations to register their log device so it
is no longer missing from the list of device dependencies.

When device mapper targets use a device they normally call dm_get_device
which includes it in the device list returned to userspace applications
such as LVM through the DM_TABLE_DEPS ioctl.  Userspace log devices
don't use dm_get_device as userspace opens them so they are missing from
the list of dependencies.

This patch extends the DM_ULOG_CTR operation to allow userspace to
respond with the name of the log device (if appropriate) to be
registered via 'dm_get_device'.  DM_ULOG_REQUEST_VERSION is incremented.

This is backwards compatible.  If the kernel and userspace log server
have both been updated, the new information will be passed down to the
kernel and the device will be registered.  If the kernel is new, but
the log server is old, the log server will not pass down any device
information and the kernel will simply bypass the device registration
as before.  If the kernel is old but the log server is new, the log
server will see the old version number and not pass the device info.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 32 insertions, 3 deletions

diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
index 3c27978..8db3862 100644
--- a/drivers/md/dm-log-userspace-base.c
+++ b/drivers/md/dm-log-userspace-base.c
@@ -30,6 +30,7 @@ struct flush_entry {
 
 struct log_c {
 	struct dm_target *ti;
+	struct dm_dev *log_dev;
 	uint32_t region_size;
 	region_t region_count;
 	uint64_t luid;
@@ -161,13 +162,15 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 	struct log_c *lc = NULL;
 	uint64_t rdata;
 	size_t rdata_size = sizeof(rdata);
+	char *devices_rdata = NULL;
+	size_t devices_rdata_size = DM_NAME_LEN;
 
 	if (argc < 3) {
 		DMWARN("Too few arguments to userspace dirty log");
 		return -EINVAL;
 	}
 
-	lc = kmalloc(sizeof(*lc), GFP_KERNEL);
+	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
 	if (!lc) {
 		DMWARN("Unable to allocate userspace log context.");
 		return -ENOMEM;
@@ -195,9 +198,19 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 		return str_size;
 	}
 
-	/* Send table string */
+	devices_rdata = kzalloc(devices_rdata_size, GFP_KERNEL);
+	if (!devices_rdata) {
+		DMERR("Failed to allocate memory for device information");
+		r = -ENOMEM;
+		goto out;
+	}
+
+	/*
+	 * Send table string and get back any opened device.
+	 */
 	r = dm_consult_userspace(lc->uuid, lc->luid, DM_ULOG_CTR,
-				 ctr_str, str_size, NULL, NULL);
+				 ctr_str, str_size,
+				 devices_rdata, &devices_rdata_size);
 
 	if (r < 0) {
 		if (r == -ESRCH)
@@ -220,7 +233,20 @@ static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 	lc->region_size = (uint32_t)rdata;
 	lc->region_count = dm_sector_div_up(ti->len, lc->region_size);
 
+	if (devices_rdata_size) {
+		if (devices_rdata[devices_rdata_size - 1] != '\0') {
+			DMERR("DM_ULOG_CTR device return string not properly terminated");
+			r = -EINVAL;
+			goto out;
+		}
+		r = dm_get_device(ti, devices_rdata,
+				  dm_table_get_mode(ti->table), &lc->log_dev);
+		if (r)
+			DMERR("Failed to register %s with device-mapper",
+			      devices_rdata);
+	}
 out:
+	kfree(devices_rdata);
 	if (r) {
 		kfree(lc);
 		kfree(ctr_str);
@@ -241,6 +267,9 @@ static void userspace_dtr(struct dm_dirty_log *log)
 				 NULL, 0,
 				 NULL, NULL);
 
+	if (lc->log_dev)
+		dm_put_device(lc->ti, lc->log_dev);
+
 	kfree(lc->usr_argv_str);
 	kfree(lc);