Re: [PATCH 31/34] vfs: syscall: Add fspick() to select a superblock for reconfiguration [ver #12]

On 17/10/2018 16:45, David Howells wrote:

Alan Jenkins [off-list ref] wrote:

quoted

I agree.  I'm happy to see this is using the same check as do_remount().


* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/

Are you suggesting that it should only work at the ultimate root of a
superblock and not a bind mount somewhere within?

That's tricky to make work for NFS because s_root is a dummy dentry.

David

Retro-actively: I do not suggest that.

I tried to answer this question in my reply to Eric correcting me.  Eric was right to correct me.  I now understand the comment above do_remount() is incorrect.  I re-reviewed your diff in light of that.  I re-endorse your diff as a way to solve the problem I raised.

(I think it would be useful to remove the misleading comment above do_remount(), to avoid future confusion.)

( the "if" statement it adds to fspick() is equivalent to the second "if" statement in do_remount(): )

static  int  do_remount <https://elixir.bootlin.com/linux/v4.18/ident/do_remount>(struct  path <https://elixir.bootlin.com/linux/v4.18/ident/path>  *path <https://elixir.bootlin.com/linux/v4.18/ident/path>,  int  ms_flags,  int  sb_flags,
		int  mnt_flags,  void  *data)
{
	int  err;
	struct  super_block <https://elixir.bootlin.com/linux/v4.18/ident/super_block>  *sb  =  path <https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt>->mnt_sb;
	struct  mount <https://elixir.bootlin.com/linux/v4.18/ident/mount>  *mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt>  =  real_mount <https://elixir.bootlin.com/linux/v4.18/ident/real_mount>(path <https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt>);

	if  (!check_mnt <https://elixir.bootlin.com/linux/v4.18/ident/check_mnt>(mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt>))
		return  -EINVAL <https://elixir.bootlin.com/linux/v4.18/ident/EINVAL>;

	if  (path <https://elixir.bootlin.com/linux/v4.18/ident/path>->dentry  !=  path <https://elixir.bootlin.com/linux/v4.18/ident/path>->mnt <https://elixir.bootlin.com/linux/v4.18/ident/mnt>->mnt_root)
		return  -EINVAL <https://elixir.bootlin.com/linux/v4.18/ident/EINVAL>;

Thanks

Alan