linux-kernel - Re: UML/hostfs - mount failure at tip of tree

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Message-ID: <20240726-burggraben-zugluft-351cfa07d2de@brauner>
Date: Fri, 26 Jul 2024 09:41:02 +0200
From: Christian Brauner <brauner@...nel.org>
To: Hongbo Li <lihongbo22@...wei.com>
Cc: Maciej Żenczykowski <maze@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, Kernel hackers <linux-kernel@...r.kernel.org>, 
	Patrick Rohr <prohr@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: UML/hostfs - mount failure at tip of tree

On Wed, Jul 24, 2024 at 05:49:16PM GMT, Hongbo Li wrote:
> 
> 
> On 2024/7/24 11:59, Maciej Żenczykowski wrote:
> > On Tue, Jul 23, 2024 at 7:55 PM Maciej Żenczykowski <maze@...gle.com> wrote:
> > > 
> > > On Tue, Jul 23, 2024 at 7:22 PM Linus Torvalds
> > > <torvalds@...ux-foundation.org> wrote:
> > > > 
> > > > On Tue, 23 Jul 2024 at 18:35, Hongbo Li <lihongbo22@...wei.com> wrote:
> > > > > 
> > > > > I apologize for causing this issue. I am currently tracking it down.  If
> > > > > reverting this can solve the problem, you can revert it first.
> > > > 
> > > > I don't get the feeling that this is _so_ urgent that it needs to be
> > > > reverted immediately - let's give it at least a few days and see if
> > > > you (or somebody else) figures out the bug.
> > > > 
> > > > Maciej - if you can verify that folio conversion fix suggestion of
> > > > mine (or alternatively report that it doesn't help and I was barking
> > > > up the wrong tree), that would be great.
> > > 
> > > That appears to fix the folio patch indeed (ie. I no longer need to revert it).
> > > 
> > > The tests are still super unhappy, but I've yet to fix our tests very
> > > broken netlink parser for changes that released in 6.10, so that may
> > > be unrelated ;-)
> > 
> > +++ fs/hostfs/hostfs_kern.c:
> >   static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
> >   {
> >          struct hostfs_fs_info *fsi = sb->s_fs_info;
> > -       const char *host_root = fc->source;
> > +       const char *host_root = "/";
> > 
> This doesn't work in case where the host directory is designated (such as
> mount -t hostfs hostfs -o /home /host).
> 
> I can fix this by the following patch, the root cause of this issue is the
> incorrect parsing of the host directory. The original mount path will use
> `parse_monolithic` to parse the host directory. For the new mount api, it
> use `parse_param` directly. So we should call `fsconfig(fd,
> FSCONFIG_SET_STRING, "hostfs", "xxx", 0)` to mount the hostfs(I think may be
> we should add hostfs as the key for host directory.). This may need
> Christian's reviews.:

I see you sent the patch. I looked at it yesterday but didn't really dig
into it. Let me go do that now. I'll have a pr ready for Linus latest
tomorrow.