dm thin: open dev read only when possible

If a thin pool is created in read-only-metadata mode then only open the
metadata device read-only.

Previously it was always opened with FMODE_READ | FMODE_WRITE.

(Note that dm_get_device() still allows read-only dm devices to be used
read-write at the moment: If I create a read-only linear device for the
metadata, via dmsetup load --readonly, then I can still create a rw pool
out of it.)

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 111c148..ef021b0 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1945,6 +1945,7 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
        unsigned long block_size;
        dm_block_t low_water_blocks;
        struct dm_dev *metadata_dev;
+       fmode_t metadata_mode;
 
        /*
         * FIXME Remove validation from scope of lock.
@@ -1956,10 +1957,22 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
                r = -EINVAL;
                goto out_unlock;
        }
+
        as.argc = argc;
        as.argv = argv;
 
-       r = dm_get_device(ti, argv[0], FMODE_READ | FMODE_WRITE, &metadata_dev);
+       /*
+        * Set default pool features.
+        */
+       pool_features_init(&pf);
+
+       dm_consume_args(&as, 4);
+       r = parse_pool_features(&as, &pf, ti);
+       if (r)
+               goto out_unlock;
+
+       metadata_mode = FMODE_READ | ((pf.mode == PM_READ_ONLY) ? 0 : FMODE_WRITE);
+       r = dm_get_device(ti, argv[0], metadata_mode, &metadata_dev);
        if (r) {
                ti->error = "Error opening metadata block device";
                goto out_unlock;
@@ -1992,16 +2005,6 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
                goto out;
        }
 
-       /*
-        * Set default pool features.
-        */
-       pool_features_init(&pf);
-
-       dm_consume_args(&as, 4);
-       r = parse_pool_features(&as, &pf, ti);
-       if (r)
-               goto out;
-
        pt = kzalloc(sizeof(*pt), GFP_KERNEL);
        if (!pt) {
                r = -ENOMEM;