fs/super.c: introduce get_tree_bdev_flags()

As Allison reported [1], currently get_tree_bdev() will store
"Can't lookup blockdev" error message.  Although it makes sense for
pure bdev-based fses, this message may mislead users who try to use
EROFS file-backed mounts since get_tree_nodev() is used as a fallback
then.

Add get_tree_bdev_flags() to specify extensible flags [2] and
GET_TREE_BDEV_QUIET_LOOKUP to silence "Can't lookup blockdev" message
since it's misleading to EROFS file-backed mounts now.

[1] https://lore.kernel.org/r/CAOYeF9VQ8jKVmpy5Zy9DNhO6xmWSKMB-DO8yvBB0XvBE7=3Ugg@mail.gmail.com
[2] https://lore.kernel.org/r/ZwUkJEtwIpUA4qMz@infradead.org



Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241009033151.2334888-1-hsiangkao@linux.alibaba.com


Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>