ext4: auto disable dax instead of failing mount

Bring the ext4 filesystem in line with xfs that only warns and continues
when the "-o dax" option is specified to mount and the backing device
does not support dax. This is in preparation for removing dax support
from devices that do not enable get_user_pages() operations on dax
mappings. In other words 'gup' support is required and configurations
that were using so called 'page-less' dax will be converted back to
using the page cache.

Removing the broken 'page-less' dax support is a pre-requisite for
removing the "EXPERIMENTAL" warning when mounting a filesystem in dax
mode.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7c46693..18873ea 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3710,11 +3710,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                if (ext4_has_feature_inline_data(sb)) {
                        ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
                                        " that may contain inline data");
-                       goto failed_mount;
+                       sbi->s_mount_opt &= ~EXT4_MOUNT_DAX;
                }
                err = bdev_dax_supported(sb, blocksize);
-               if (err)
-                       goto failed_mount;
+               if (err) {
+                       ext4_msg(sb, KERN_ERR,
+                               "DAX unsupported by block device. Turning off DAX.");
+                       sbi->s_mount_opt &= ~EXT4_MOUNT_DAX;
+               }
        }
 
        if (ext4_has_feature_encrypt(sb) && es->s_encryption_level) {