multipath devices are not getting created for readonly devices

Commit Message

Hannes Reinecke March 12, 2014, 11:34 a.m. UTC

Currently we cannot create device-mapper tables for multipath devices
whenever the underlying devices are read-only.
This patch modifies the device-mapper to set the 'READ-ONLY' flag
automatically whenever a read-only device is added to the table.

Signed-off-by: Hannes Reinecke <[e-mail]>
---
 drivers/md/dm-table.c | 11 ++++++++++-
 drivers/md/dm.c       | 17 +++++++++++++++--
 2 files changed, 25 insertions(+), 3 deletions(-)

Comments

Alasdair G Kergon March 12, 2014, 12:18 p.m. UTC | #1

On Wed, Mar 12, 2014 at 12:34:54PM +0100, Hannes Reinecke wrote:
> Currently we cannot create device-mapper tables for multipath devices
> whenever the underlying devices are read-only.

Userspace can specify a read-only table when creating it.

> This patch modifies the device-mapper to set the 'READ-ONLY' flag
> automatically whenever a read-only device is added to the table.
 
I don't know if it's working properly at the moment, but some targets
(like dm-delay) are meant to work with a combination of read-only and
read-write devices. 

I don't think the table mode should get changed quite like this: I
think this problem needs wider review, perhaps overlapping with the
problem of checking on the I/O path not just at device open time.

Alasdair

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Patch

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 6a7f2b8..44ea2b3 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -443,11 +443,20 @@  int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 		dd->dm_dev.mode = mode;
 		dd->dm_dev.bdev = NULL;
 
-		if ((r = open_dev(dd, dev, t->md))) {
+		r = open_dev(dd, dev, t->md);
+		if (r == -EROFS) {
+			dd->dm_dev.mode &= ~FMODE_WRITE;
+			r = open_dev(dd, dev, t->md);
+		}
+		if (r) {
 			kfree(dd);
 			return r;
 		}
 
+		/* Modify the table mode, too */
+		if (dd->dm_dev.mode != mode)
+			t->mode = dd->dm_dev.mode;
+
 		format_dev_t(dd->dm_dev.name, dev);
 
 		atomic_set(&dd->count, 0);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8c53b09..0f7b441 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -384,16 +384,25 @@  int dm_deleting_md(struct mapped_device *md)
 static int dm_blk_open(struct block_device *bdev, fmode_t mode)
 {
 	struct mapped_device *md;
+	int retval = 0;
 
 	spin_lock(&_minor_lock);
 
 	md = bdev->bd_disk->private_data;
-	if (!md)
+	if (!md) {
+		retval = -ENXIO;
 		goto out;
+	}
 
 	if (test_bit(DMF_FREEING, &md->flags) ||
 	    dm_deleting_md(md)) {
 		md = NULL;
+		retval = -ENXIO;
+		goto out;
+	}
+	if (get_disk_ro(md->disk) && (mode & FMODE_WRITE)) {
+		md = NULL;
+		retval = -EROFS;
 		goto out;
 	}
 
@@ -403,7 +412,7 @@  static int dm_blk_open(struct block_device *bdev, fmode_t mode)
 out:
 	spin_unlock(&_minor_lock);
 
-	return md ? 0 : -ENXIO;
+	return retval;
 }
 
 static void dm_blk_close(struct gendisk *disk, fmode_t mode)
@@ -2156,6 +2165,10 @@  static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 		set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
 	else
 		clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
+	if (!(dm_table_get_mode(t) & FMODE_WRITE))
+		set_disk_ro(md->disk, 1);
+	else
+		set_disk_ro(md->disk, 0);
 	dm_sync_table(md);
 
 	return old_map;