What are the memory address restrictions when using the O_DIRECT flag
with XFS? I am trying to perform I/O directly from the filesystem to a piece
of mmap'ed video memory and I get the "bad address" error when I attempt to
do so with O_DIRECT. Without the O_DIRECT flag I am able to perform the I/O
but is it must too slow. Using O_DIRECT with other system memory seems to
work fine, but I would like the option of transferring data directly to a
video card without a bounce buffer and a DMA step. Is direct I/O available
to any memory address that satisfies the alignment requirement or must this
address be below the MAX_DMA_ADDR?
Any help appreciated. Thanks.
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