Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 29 Nov 2018 10:53:32 -0800 | Subject | Re: remove the ->mapping_error method from dma_map_ops V2 |
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On Thu, Nov 29, 2018 at 10:31 AM Christoph Hellwig <hch@lst.de> wrote: > > > Or, better yet, plan on removing the single-page dma mappign entirely > > at a later date, and make the issue moot. > > What would be the replacement? Build a S/G list for every single page > mapping? Not sure that would create a lot of happy campers..
It's what we ended up doing with some other cases, and it didn't really end up hurting as much as I thought it would.
I'm thinking of the vfs functions that end up turning "buf, len" into
struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = len };
and then passing it around as a single-entry iov instead (not even that - they end up being an iov_iter, which is not just the iov, but the whole "what _kind_ of iov" indirection)
Maybe a very similar model could be used for just simplifying the core dma mapping setup: sure, people will want to do single-area dma, but how bad would it be to just turn them into single-entry SG lists on stack, and then the dma-maping internally would just always see that?
Most of the high-performance IO is already using SG lists anyway, no? Disk/networking/whatever.
But just an idea. And the "map_sg()" error handling isn't actually any better, I think. It returns zero on error, no? So it's not improving the error handling.
The whole dma-mapping layer seems full of those kinds of "inspired error handling choices" ;)
Linus
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