Messages in this thread |  | | Date | Sat, 29 Dec 2001 10:46:04 -0800 | | From | CJ <> | | Subject | Re: Possible O_DIRECT problems ? |
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Shouldn't O_DIRECT's requirements come from the hardware? If we can ASPI or CAM DMA SCSI devices to odd addresses and lengths, why not O_DIRECT? Do ape drives DMA to user buffers? Are O_DIRECT's current limits gratuitous?
Andrea Arcangeli wrote:
>On Fri, Dec 21, 2001 at 12:39:42AM +0000, Dave Jones wrote: > >>On Fri, Dec 21, 2001 at 01:23:45AM +0100, Trond Myklebust wrote: >> >> > O_DIRECT for NFS isn't yet merged into the kernel. Are these Chuck >> > Lever's NFS patches you've been testing? >> >>Nope, stock 2.4.17rc2 & 2.5.1. >>I thought NFS might just ignore the O_DIRECT flag if it didn't >>understand it yet, I wasn't expecting such a dramatic failure. >> > >The point of O_DIRECT is to do DMA directly into the userspace memory >(and to avoid the VM overhead but that's a secondary issue and with data >journaling we may need to put an anchor into the VM to serialize the >direct I/O with the pagecache I/O in a secondary - slower - direct_IO >callback for the data journaling fs). > >But to avoid the mem copies you're required to use strict alignment and >size of the userspace buffers, just like rawio. > >If you don't you will get -EINVAL. This ensures people will use O_DIRECT >correctly in their apps. In short every single bugreport like this about >this -EINVAL strict behaviour is the proof we need to be strict and to >return -EINVAL :) > >Andrea >- >To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html >Please read the FAQ at http://www.tux.org/lkml/ > >. >
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