Re: [PATCH 12/18] io_uring: add support for pre-mapped user IO buffers
flat view
From: Jeff Moyer <hidden>
Date: 2019-02-07 22:38:37
Also in:
linux-block
Hi, Jens, Jens Axboe [off-list ref] writes:
For now, buffers must not be file backed. If file backed buffers are passed in, the registration will fail with -1/EOPNOTSUPP. This restriction may be relaxed in the future.
[...]
quoted hunk
+ down_write(¤t->mm->mmap_sem); + pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE, + pages, vmas); + if (pret == nr_pages) { + /* don't support file backed memory */ + for (j = 0; j < nr_pages; j++) { + struct vm_area_struct *vma = vmas[j]; + + if (vma->vm_file) { + ret = -EOPNOTSUPP; + break; + } + }
Unfortunately, this suffers the same problem as FOLL_ANON. Huge pages
are backed by hugetlbfs, and vma->vm_file will be filled in.
I guess you could check is_file_hugepages(vma->vm_file):
if (vma->vm_file &&
!is_file_hugepages(vma->vm_file)) {
ret = -EOPNOTSUPP;
break;
}
That works for me.
-Jeff
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