Messages in this thread | | | Date | Thu, 3 Jun 1999 21:40:49 +0200 (MET DST) | From | Gerard Roudier <> | Subject | Re: accessing raw disk. |
| |
Hello,
On Wed, 2 Jun 1999, Stephen C. Tweedie wrote:
> Hi, > > On Wed, 2 Jun 1999 20:18:27 +0200 (MET DST), Gerard Roudier > <groudier@club-internet.fr> said: > > > Thanks, Stephen, for your raw-io patch. > > > It does work, but refuses to work for me with non sector-size aligned > > buffer address. > > That's correct: this is expected behaviour for Unix raw character > devices. You are doing dma from memory to disk, so the application > needs to do the alignment normally done by the OS.
A requirement that is not needed is called a limitation.
> > If the IO is broken into several ones, perhaps this condition would > > be required, but it seems to me that only the total IO length has to > > be a multiple of the sector-size. > > You might be talking to a device which cannot scatter-gather, or which > can scatter-gather only on block boundaries.
I might but I don't, and so I am not happy to be imposed limitations I donnot deserve to suffer of.
> Remember that the > virtual memory is not going to be physically contiguous.
I donnot have to remember for that point. Btw, there is some parts in the kernel that seem not to care enough about the virtual/physical issue, in my opinion.
> > I have implemented recently the support of unaligned Wide Transfers in the > > sym53c8xx driver and I need something that provides some oddly aligned > > buffers to test the driver code. If it is possible to remove the checking > > of buffer alignment in your code without serious breakage, > > It will break the code, since there is absolutely no support anywhere > in the kernel for submitting an IO to a single disk block from a > scatter-gather buffer.
Indeed, that is the issue. The ll_rw_blk thing and the current kernel interfaces with IO sub-systems are the problems.
Your raw-io implementation is fine with regards to exiting kernel interfaces. Thanks again for this very interesting feature.
Regards, Gérard.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
| |