use `sendfile` instead

[oriongonza]

An mvp of sendfile copying. https://github.com/dev-ardi/sendfile_rs

[SUPERCILEX]

We use copy_file_range().

[oriongonza]

Why close this? my implementation is about 3 times faster than cpz on my machine. It's worth looking into I think.

[SUPERCILEX]

What's the benchmark? If it's a super small file, then were probably slow from some overhead on startup. If the file is large, then my guess is that you're not actually copying it since you don't loop sendfile. Check that the input and output file sizes match.

[oriongonza]

It was a 6.1GB .iso file from one partition into another, it copied correctly.

[SUPERCILEX]

Hmmm, can you try swapping your sendfile call for https://docs.rs/libc/latest/libc/fn.copy_file_range.html and seeing if it's slower? And what kernel version are you on (uname -a)? Also, could you please run cpz with strace (strace cpz ...) and share the output?

[oriongonza]

at 15:15:27 ❯ time target/release/ddrs --input ~/Downloads/windows.iso --output windows.iso

________________________________________________________
Executed in    2.27 secs    fish           external
   usr time    0.00 secs  284.00 micros    0.00 secs
   sys time    1.29 secs    0.00 micros    1.29 secs

at 15:16:15 ❯ time cpz ~/Downloads/windows.iso windows.iso  --force

________________________________________________________
Executed in    9.84 secs    fish           external
   usr time    0.10 secs  228.00 micros    0.10 secs
   sys time    4.63 secs  121.00 micros    4.63 secs

Using copy_file_range I get this error: Invalid cross-device link (os error 18)

[SUPERCILEX]

Ah, ok so my guess is that you're on an old kernel. Version please? Also I'll need to look into the stdlib because it looks like they don't have a sendfile fallback. Also I don't think we fallback to sendfile which is unfortunate.

[oriongonza]

at 15:40:36 ❯ uname -a
Linux arch 6.12.3-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 06 Dec 2024 11:15:43 +0000 x86_64 GNU/Linux

as new as it gets. As I mentioned this is copying from one partition into another.

[SUPERCILEX]

Ok clearly I need to add cross device fallbacks for when copy_file_range isn't available.