UML mount failure with Linux 6.11

[Johannes Berg]

On Thu, 2024-11-07 at 22:17 +0800, Hongbo Li wrote:
> > There's only one option anyway, so I'd think we just need to fix this
> > and not require the hostfs= key. Perhaps if and only if it starts with
> > hostfs= we can treat it as a key, otherwise treat it all as a dir? But I
> 
> May be we can do that (just record the unknown option in host_root_path 
> when fs_parse failed). But this lead us to consider the case in which we 
> should handle a long option -o unknown1,hostfs=xxx,unknow2, which one 
> should be treated as the root directory? For new mount api, it will call 
> fsconfig three times to set the root directory. For older one, if one 
> path with that name exactly, may be it can mount successfully.

Technically, comma _is_ valid in a dir name, as you say ... so perhaps
the new mount API handling would need to be modified to have an escape
for this and not split it automatically, if the underlying FS doesn't
want that? Or we just revert cd140ce9f611 too?

I feel like perhaps we just found a corner case - clearly the new mount
API assumes that mount options are always comma-separated, but, well,
turns out that's simply not true since hostfs has only a single option
and treats the whole thing as a single string.

johannes