Date: Sat, 24 Aug 2013 08:24:29 +0100 From: Daichi GOTO <daichi@ongs.co.jp> To: =?utf-8?Q?Jaume_Mart=C3=AD?= <jaume.martif@gmail.com> Cc: freebsd-fs@freebsd.org, daichi@freebsd.org Subject: Re: Possible approach to fix PR 172334. Message-ID: <E93BFE23-22B4-46A0-8336-0455F7999BF7@ongs.co.jp> In-Reply-To: <CAL4g94T645j_%2BpazUWa0CwfKSEUtF_%2ByjUoEbshDbtozqkK3aA@mail.gmail.com> References: <CAL4g94T645j_%2BpazUWa0CwfKSEUtF_%2ByjUoEbshDbtozqkK3aA@mail.gmail.com>
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Hi Jaume, thanks for your suggestion. I think that we should discuss your suggestion on freebsd-fs mailing list with filesystems folks. If you do not subscribe the freebsd-fs, please join it. And filesystem folks, what do you make of this suggestion? On 2013/08/23, at 16:41, Jaume Martí <jaume.martif@gmail.com> wrote: > Hello Daichi, > > I contact you regarding PR 172334 (http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/172334). > I am interested in implementing a fix for this issue and I have been thinking on a solution reusable for other file systems. > I would add a new operation in struct vop_vector that returns a list of vnodes. > This operation would only make sense on vnodes from file systems that use other vnodes instead of directly storing the data in a disk. > In the case of unionfs the return value would be a list with the corresponding vnodes from the upper and/or lower layers where this vnode is mapped. > > Using this operation it could be possible to traverse the vnode dependency graph and look for loops. > In the case of the unionfs, it could be implemented in the domount function a check to see if it is possible to reach on the dependency graph the lowerrootvp starting from the upperrootvp, or viceversa, using a simple graph traversal algorithm. > > I would like to know your opinion on this solution, and if you consider it is good enough to be eventually committed to the FreeBSD src tree. > I am not an expert on the FreeBSD kernel nor on unionfs so please, feel free to suggest any change you consider necessary to my approach. > > Best regards, > Jaume -- Daichi GOTO, daichi@freebsd.org
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