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Re: [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED

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On Thu, Aug 24, 2017 at 11:00 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Thu, Aug 24, 2017 at 9:13 AM, Christoph Hellwig <hch@lst.de> wrote:
>> I'm still very unhappy about the get/set flag state.  What is the
>> reason you can't use/extend leases? (take a look at the fcntl
>> man page and look for Leases).  A variant of the concept is what
>> the pNFS block server uses.
>
> So I think leases could potentially be extended to replace the inode
> flag. A MAP_DIRECT operation would take out a lease that is broken by
> break_layouts(). However, like the pNFS case the lease break would
> need to held off while any DMA might be in-flight. We can use an
> elevated page count as that indication as ZONE_DEVICE pages only ever
> have an elevated page count in response to get_user_pages().
>
> However, I think the only practical difference is turning an immediate
> ETXTBSY response that S_IOMAP_SEALED provides into an indefinite
> blocking wait for break_layouts() to complete. Can pNFS run
> break_layouts() in bounded time?
>
> As far I can see a lease and S_IOMAP_SEALED have the same DMA
> cancelling problem, so a lease is not better in that regard. Absent an
> overlaying protocol like pNFS, I think S_IOMAP_SEALED is cleaner
> because it fails incompatible operations outright rather than stalls
> them in break_layouts(). Were their other benefits to a lease over an
> inode flag that you had in mind for this case where the protocol is
> userspace defined? Maybe I'm thinking too small on the ways a lease
> might be extended.

At a minimum I can at least use a new lease type as an indication of
when to bail out an block-map operation with ETXTBSY, and reuse the
lease security model. That way we at least start to converge the
in-kernel lease machinery for pinning blocks with this userspace
mechanism.

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[PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Dan Williams <dan.j.williams@intel.com> - 2017-08-24 02:00 +0200
  [PATCH v6 4/5] fs,  xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges Dan Williams <dan.j.williams@intel.com> - 2017-08-24 02:00 +0200
    Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating         block-map-atomic file ranges Christoph Hellwig <hch@lst.de> - 2017-08-24 18:20 +0200
      Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating         block-map-atomic file ranges Christoph Hellwig <hch@lst.de> - 2017-08-24 18:40 +0200
        Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating  block-map-atomic file ranges Dan Williams <dan.j.williams@intel.com> - 2017-08-24 22:30 +0200
      Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating  block-map-atomic file ranges Dan Williams <dan.j.williams@intel.com> - 2017-08-24 18:40 +0200
  [PATCH v6 5/5] fs, fcntl: add F_MAP_DIRECT Dan Williams <dan.j.williams@intel.com> - 2017-08-24 02:00 +0200
  [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Dan Williams <dan.j.williams@intel.com> - 2017-08-24 02:00 +0200
    Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Jan Kara <jack@suse.cz> - 2017-08-24 15:10 +0200
    Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Christoph Hellwig <hch@infradead.org> - 2017-08-24 19:00 +0200
      Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-08-24 19:40 +0200
        Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Christoph Hellwig <hch@infradead.org> - 2017-08-25 15:10 +0200
          Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-08-25 18:00 +0200
            Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Christoph Hellwig <hch@infradead.org> - 2017-08-25 18:10 +0200
              Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-08-25 18:20 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Helge Deller <deller@gmx.de> - 2017-08-25 18:30 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-08-25 19:00 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-08-25 22:30 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Helge Deller <deller@gmx.de> - 2017-08-26 09:50 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-08-26 17:20 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags Helge Deller <deller@gmx.de> - 2017-08-26 22:00 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams <dan.j.williams@intel.com> - 2017-08-27 00:50 +0200
                Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap  flags "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-08-27 02:00 +0200
  [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Dan Williams <dan.j.williams@intel.com> - 2017-08-24 02:00 +0200
    Re: [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Christoph Hellwig <hch@lst.de> - 2017-08-24 18:20 +0200
      Re: [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Dan Williams <dan.j.williams@intel.com> - 2017-08-25 08:10 +0200
        Re: [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Dan Williams <dan.j.williams@intel.com> - 2017-08-25 21:50 +0200
  Re: [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Christoph Hellwig <hch@lst.de> - 2017-08-24 18:10 +0200
    Re: [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Dan Williams <dan.j.williams@intel.com> - 2017-08-24 18:30 +0200
  Re: [PATCH v6 1/5] vfs: add flags parameter to ->mmap() in 'struct  file_operations' Christoph Hellwig <hch@infradead.org> - 2017-08-24 19:00 +0200
    Re: [PATCH v6 1/5] vfs: add flags parameter to ->mmap() in 'struct file_operations' Dan Williams <dan.j.williams@intel.com> - 2017-08-24 19:50 +0200

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