When shared domain is enabled, doing mount twice with the same fsid and
domain_id will trigger sysfs warning as shown below:

 sysfs: cannot create duplicate filename '/fs/erofs/d0,meta.bin'
 CPU: 15 PID: 1051 Comm: mount Not tainted 6.1.0-rc6+ #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
 Call Trace:
  <TASK>
  dump_stack_lvl+0x38/0x49
  dump_stack+0x10/0x12
  sysfs_warn_dup.cold+0x17/0x27
  sysfs_create_dir_ns+0xb8/0xd0
  kobject_add_internal+0xb1/0x240
  kobject_init_and_add+0x71/0xa0
  erofs_register_sysfs+0x89/0x110
  erofs_fc_fill_super+0x98c/0xaf0
  vfs_get_super+0x7d/0x100
  get_tree_nodev+0x16/0x20
  erofs_fc_get_tree+0x20/0x30
  vfs_get_tree+0x24/0xb0
  path_mount+0x2fa/0xa90
  do_mount+0x7c/0xa0
  __x64_sys_mount+0x8b/0xe0
  do_syscall_64+0x30/0x60
  entry_SYSCALL_64_after_hwframe+0x46/0xb0

The reason is erofs_fscache_register_cookie() doesn't guarantee the primary
data blob (aka fsid) is unique in the shared domain and
erofs_register_sysfs() invoked by the second mount will fail due to the
duplicated fsid in the shared domain and report warning.

It would be better to check the uniqueness of fsid before doing
erofs_register_sysfs(), so adding a new flags parameter for
erofs_fscache_register_cookie() and doing the uniqueness check if
EROFS_REG_COOKIE_NEED_NOEXIST is enabled.

After the patch, the error in dmesg for the duplicated mount would be:

 erofs: ...: erofs_domain_register_cookie: XX already exists in domain YY
Reviewed-by: Jia Zhu <zhujia.zj@bytedance.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20221125110822.3812942-1-houtao@huaweicloud.com
Fixes: 7d419637 ("erofs: Support sharing cookies in the same domain")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>