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Date: Fri, 22 May 2020 20:56:26 +0100 From: Al Viro <viro@...iv.linux.org.uk> To: Miklos Szeredi <mszeredi@...hat.com> Cc: Amir Goldstein <amir73il@...il.com>, overlayfs <linux-unionfs@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] ovl: make private mounts longterm On Fri, May 22, 2020 at 08:53:49PM +0200, Miklos Szeredi wrote: > On Fri, May 22, 2020 at 7:02 PM Amir Goldstein <amir73il@...il.com> wrote: > > > > > > > - mntput(ofs->upper_mnt); > > > > > - for (i = 1; i < ofs->numlayer; i++) { > > > > > - iput(ofs->layers[i].trap); > > > > > - mntput(ofs->layers[i].mnt); > > > > > + > > > > > + if (!ofs->layers) { > > > > > + /* Deal with partial setup */ > > > > > + kern_unmount(ofs->upper_mnt); > > > > > + } else { > > > > > + /* Hack! Reuse ofs->layers as a mounts array */ > > > > > + struct vfsmount **mounts = (struct vfsmount **) ofs->layers; > > > > > + > > > > > + for (i = 0; i < ofs->numlayer; i++) { > > > > > + iput(ofs->layers[i].trap); > > > > > + mounts[i] = ofs->layers[i].mnt; > > > > > + } > > > > > + kern_unmount_many(mounts, ofs->numlayer); > > > > > + kfree(ofs->layers); > > > > > > > > That's _way_ too subtle. AFAICS, you rely upon ->upper_mnt == ->layers[0].mnt, > > > > ->layers[0].trap == NULL, without even mentioning that. And the hack you do > > > > mention... Yecchhh... How many layers are possible, again? > > > > > > 500, mounts array would fit inside a page and a page can be allocated > > > with __GFP_NOFAIL. But why bother? It's not all that bad, is it? > > > > FWIW, it seems fine to me. > > We can transfer the reference from upperdir_trap to layers[0].trap > > when initializing layers[0] for the sake of clarity. > > Right, we should just get rid of ofs->upper_mnt and ofs->upperdir_trap > and use ofs->layers[0] to store those. For that you'd need to allocate ->layers before you get to ovl_get_upper(), though. I'm not saying it's a bad idea - doing plain memory allocations before anything else tends to make failure exits cleaner; it's just that it'll take some massage. Basically, do ovl_split_lowerdirs() early, then allocate everything you need, then do lookups, etc., filling that stuff. Regarding this series - the points regarding the name choice and the need to document the calling conventions change still remain.
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