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Merovius opened this issue Dec 18, 2019 · 7 comments
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x/sys/unix: Add wrapper for readv/writev #36201

Merovius opened this issue Dec 18, 2019 · 7 comments
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@Merovius
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Merovius commented Dec 18, 2019 •
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I'd like to propose exposing readv/writev (and maybe preadv/pwritev and maybeer preadv2/pwritev2) in x/sys/unix, as {Read,Write}v(fd int, iov [][]byte) (int, error).

My usecase is writing to a file in O_APPEND mode, which offers atomicity-guarantees per write. Issuing multiple writes loses those guarantees, so I have to resort to a) allocating a temporary buffer and concatenating the individual []bytes, or b) use unix.Syscall. The latter is fine, but a wrapper would allow to avoid unsafe.

I don't personally care about the p… and …v2 variants, but they could be added at the same time. I'm not sure how portable they are, though, beyond Linux.

I can send a CL if this is accepted.
@gopherbot gopherbot added this to the Unreleased milestone Dec 18, 2019
@Merovius
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Merovius commented Dec 18, 2019 •
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(See also #21676 which discusses, among other things, exposing an interface to writev for *os.File)

@ianlancetaylor
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In general we permit adding any existing system call to x/net/unix. Using [][]byte as the second argument seems right to me. So this is fine.

@ianlancetaylor ianlancetaylor added help wanted NeedsFix The path to resolution is known, but the work has not been done. labels Dec 19, 2019
@tklauser tklauser changed the title x/net/unix: Add wrapper for readv/writev x/sys/unix: Add wrapper for readv/writev Dec 19, 2019
@tklauser
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I assume you meant x/sys/unix, not x/net/unix?

It's fine to add the non-portable preadv/pwritev/preadv2/pwritev2 variants for Linux only. We already have several wrappers for Linux-only syscalls.

@Merovius
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Merovius commented Dec 19, 2019 •
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@tklauser yes I do, thanks, corrected my initial post as well :) I'll send a CL later today.

@gopherbot
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Change https://golang.org/cl/212157 mentions this issue: unix: add Readv/Writev family of syscalls for linux

@Merovius
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I only have Linux machines, so AIUI I can't generate the constants and everything for other platforms.
Also, I mostly copied the interaction with the race-detector from Read/Write - I have no idea if that was needed or correct in this case.

YoukouTenhouin pushed a commit to YoukouTenhouin/sys that referenced this issue Mar 20, 2020
unix: Add readv/writev for illumos
0c1c77c 
iovec read/writes (readv, writev, preadv, pwritev) are present on illumos,
but they weren't added to the package. This commit added those missing
features.

Updates golang/go#36201
@YoukouTenhouin YoukouTenhouin mentioned this issue Mar 20, 2020
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@gopherbot
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Change https://golang.org/cl/224238 mentions this issue: unix: Add readv/writev for illumos

gopherbot pushed a commit to golang/sys that referenced this issue Mar 21, 2020
@tklauser
unix: add readv/writev for illumos
328b4cd 
iovec read/writes (readv, writev, preadv, pwritev) are present on
illumos, but they weren't added to the package. This commit adds
those missing features.

Updates golang/go#36201

Change-Id: Iecf2bab7ef846f5ca5d693e833491d819618c15d
GitHub-Last-Rev: 81a479f
GitHub-Pull-Request: #64
Reviewed-on: https://go-review.googlesource.com/c/sys/+/224238
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
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