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specialize io::copy to use copy_file_range, splice or sendfile #75272

Merged
merged 13 commits into from
Nov 14, 2020
Merged

specialize io::copy to use copy_file_range, splice or sendfile #75272

merged 13 commits into from
Nov 14, 2020

Commits on Nov 13, 2020

  1. specialize io::copy to use copy_file_range, splice or sendfile 

    Currently it only applies to linux systems. It can be extended to make use
of similar syscalls on other unix systems.
    @the8472
    the8472 committed Nov 13, 2020
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  2. hide unused exports on other platforms

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    the8472 committed Nov 13, 2020
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  3. move tests module into separate file

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    the8472 committed Nov 13, 2020
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  4. prioritize sendfile over splice since it results in fewer context swi… 

    …tches when sending to pipes

splice returns to userspace when the pipe is full, sendfile
just blocks until it's done, this can achieve much higher throughput
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  5. add forwarding specializations for &mut variants 

    `impl Write for &mut T where T: Write`, thus the same should
apply to the specialization traits
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  6. reduce syscalls by inferring FD types based on source struct instead … 

    …of calling stat()

also adds handling for edge-cases involving large sparse files where sendfile could fail with EOVERFLOW
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    the8472 committed Nov 13, 2020
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  7. add benchmarks

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    the8472 committed Nov 13, 2020
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  8. move copy specialization into sys::unix module

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    the8472 committed Nov 13, 2020
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  9. move copy specialization tests to their own module

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    the8472 committed Nov 13, 2020
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  10. limit visibility of copy offload helpers to sys::unix module

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    the8472 committed Nov 13, 2020
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  11. move sendfile/splice/copy_file_range into kernel_copy module

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    the8472 committed Nov 13, 2020
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  12. do direct splice syscall and probe availability to get android builds… 

    … to work

Android builds use feature level 14, the libc wrapper for splice is gated
on feature level 21+ so we have to invoke the syscall directly.
Additionally the emulator doesn't seem to support it so we also have to
add ENOSYS checks.
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  13. Always handle EOVERFLOW by falling back to the generic copy loop 

    Previously EOVERFLOW handling was only applied for io::copy specialization
but not for fs::copy sharing the same code.

Additionally we lower the chunk size to 1GB since we have a user report
that older kernels may return EINVAL when passing 0x8000_0000
but smaller values succeed.
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