Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 9 Sep 2021 14:56:18 -0700 | Subject | Re: [git pull] iov_iter fixes |
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On Thu, Sep 9, 2021 at 2:39 PM Jens Axboe <axboe@kernel.dk> wrote: > > OK, one that I immediately found is just doing O_DIRECT to a block > device or file on XFS. As pages are mapped and added, the iov_iter is > advanced. If we then go and submit and get -EAGAIN, for example, then we > return with what we mapped already consumed.
Ok, that's annoying but understandable. Dave points to a commit that removes one of the EAGAIN cases, but apparently not some others.
I do kind of wonder if you can't have the exact same case when *some* of the IO succeeds, though.
IOW, can't we have that
ret = io_iter_do_read(req, iter);
return partial success - and if XFS does that "update iovec on failure", I could easily see that same code - or something else - having done the exact same thing.
Put another way: if the iovec isn't guaranteed to be coherent when an actual error occurs, then why would it be guaranteed to be coherent with a partial success value?
Because in most cases - I'd argue pretty much all - those "partial success" cases are *exactly* the same as the error cases, it's just that we had a loop and one or more iterations succeeded before it hit the error case.
Hmm?
Linus
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