NFS directio

[Olaf Kirch <okir@suse.de>]

In recent kernels, NFS direct IO limits the size of a request to
4096 pages, ie 16M on most platforms. This causes growisofs from the
dvd+rw-tools package (http://fy.chalmers.se/~appro/linux/DVD+RW/) to fail.
Its builtin "dd" style function uses 32M buffers by default.

It puzzled me a lot that it is returning -EFBIG, which means "file too
big". At least that should be EINVAL, I think. EFBIG should be reserved
for problems related to largefile support, IMO.

We can easily work around the problem by restricting the buffer size
growisofs uses on NFS, but that feels strange. I think the right way
would be to increase MAX_DIRECTIO_SIZE, and if someone submits a bigger
request, to loop and do that in MAX_DIRECTIO_SIZE chunks.

Comments?

Thanks,
Olaf
-- 
Olaf Kirch   |  --- o --- Nous sommes du soleil we love when we play
okir@suse.de |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax


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