Re: [PATCH 0/3] iopmem : A block device for PCIe memory

Sagi Grimberg
2016-10-27T10:22:49Z

>> You do realise that local filesystems can silently change the
>> location of file data at any point in time, so there is no such
>> thing as a "stable mapping" of file data to block device addresses
>> in userspace?
>>
>> If you want remote access to the blocks owned and controlled by a
>> filesystem, then you need to use a filesystem with a remote locking
>> mechanism to allow co-ordinated, coherent access to the data in
>> those blocks. Anything else is just asking for ongoing, unfixable
>> filesystem corruption or data leakage problems (i.e. security
>> issues).
>
> And at least for XFS we have such a mechanism :) E.g. I have a
> prototype of a pNFS layout that uses XFS+DAX to allow clients to do
> RDMA directly to XFS files, with the same locking mechanism we use
> for the current block and scsi layout in xfs_pnfs.c.

Christoph, did you manage to leap to the future and solve the
RDMA persistency hole? :)

e.g. what happens with O_DSYNC in this model? Or you did
a message exchange for commits?