Messages in this thread | | | Date | Fri, 4 Jun 2021 18:24:07 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2 2/2] mm: adds NOSIGBUS extension to mmap() |
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On Fri, Jun 04, 2021 at 12:43:22AM -0700, Ming Lin wrote: > Adds new flag MAP_NOSIGBUS of mmap() to specify the behavior of > "don't SIGBUS on fault". Right now, this flag is only allowed > for private mapping.
That's not what your use case asks for.
SIGBUS can be generated for a number of reasons, not only on fault beyond end-of-file. vmf_error() would convert any errno, except ENOMEM to VM_FAULT_SIGBUS.
Do you want to ignore -EIO or -ENOSPC? I don't think so.
> For MAP_NOSIGBUS mapping, map in the zero page on read fault > or fill a freshly allocated page with zeroes on write fault.
I don't like the resulting semantics: if you had a read fault beyond EOF and got zero page, you will still see zero page even if the file grows. Yes, it's allowed by POSIX for MAP_PRIVATE to get out-of-sync with the file, but it's not what users used to.
It might be enough for the use case, but I would rather avoid one-user features.
-- Kirill A. Shutemov
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