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Date: Wed, 12 Sep 2012 13:11:28 -0400 From: "J. Bruce Fields" <bfields@...ldses.org> To: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> Cc: Namjae Jeon <linkinjeon@...il.com>, "Steven J. Magnani" <steve@...idescorp.com>, Al Viro <viro@...iv.linux.org.uk>, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, Namjae Jeon <namjae.jeon@...sung.com>, Ravishankar N <ravi.n1@...sung.com>, Amit Sahrawat <a.sahrawat@...sung.com> Subject: Re: [PATCH v2 1/5] fat: allocate persistent inode numbers On Thu, Sep 13, 2012 at 02:03:51AM +0900, OGAWA Hirofumi wrote: > "J. Bruce Fields" <bfields@...ldses.org> writes: > > >> > Supposing, the server/client state is after cold boot, and client try to > >> > rename at first without any cache on client/server. > >> > > >> > Even if this state, does the server return ESTALE? If it doesn't return > >> > ESTALE, I can't understand why it is really unfixable. > >> Hi OGAWA. > >> Server will not return ESTALE in this case. because the client does > >> not have any information for files yet. > > > > It does if the client mounted before the server rebooted. NFS is > > designed so that servers can reboot without causing clients to fail. > > (Applications will just see a delay during the reboot.) > > > > It probably isn't possible to this work in the case of fat. > > > > But from fat's point of view there probably isn't much difference > > between a filehandle lookup after a reboot and a filehandle lookup after > > the inode's gone from cache. > > This is talking about to retry by client side, not server side solution. > What happens if client retry after got ESTALE? (Yes, this would not be > the solution for all NFS clients. But, I guess this solution can be for > linux NFS client.) > > > I really don't see what you can do to help here. Won't anything that > > allows looking up an uncached inode by filehandle also risk finding the > > wrong file? > > On other view (as server side solution), we are thinking there is > possible to make the stable filehandle on FAT if we disabled some > operations (e.g. rename(), unlink()) which change inode location in FAT. > > Yes, it would be stable, but supporting limited operations. > > This is server side solution, and we comparing it with client solution. Is that useful to anyone? > >> > If it returns ESTALE, why does it return? I'm assuming the previous code > >> > path is the cached FH path. > >> The main point for observation is the file handle-which is used for > >> all the NFS operation. > >> So for all the NFS operation(read/write....) which makes use of the > >> NFS file handle in between if there is a change in inode number > >> It will result in ESTALE. > >> Changing inode number on rename happened at NFS server by inode cache > >> eviction with memory pressure. > >> > >> lookupcache is used at NFS client to reduce number of LOOKUP operations. > >> But , we can still get ESTALE if inode number at NFS Server change > >> after LOOKUP, although lookupcache is disable. > >> > >> LOOKUP return NFS FH->[inode number changed at NFS Server] -> > >> But we still use old NFS FH returned from LOOKUP for any file > >> operation(write,read,etc..) > >> -> ESTALE will be returned. > > Yes. And I'm expecting as client side solution, > > -> ESTALE will be returned -> discard old FH -> restart from LOOKUP -> > make cached inode -> use returned new FH. > > Yeah, I know this is unstable (there is no perfect solution for now), You may end up with a totally different file, of course: client: server: open "/foo/bar" rename "/foo/baz"->"/foo/bar" write to file And now we're writing to the file that was originally named /foo/baz when we should have gotten ESTALE. --b. > but if this works, this doesn't limit any operations. > > We would want to compare client solution (-mm) and server solution > (stable ino). Or I'd like to know which my knowledges/understanding are > wrong here. > -- > OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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