GHOST/wayland: create temporary file manually for older kernel versions
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Authored by Christian Rauch (christian.rauch) on Jul 13 2021, 1:04 AM.

Details

Reviewers

Campbell Barton (campbellbarton)
Brecht Van Lommel (brecht)

Summary

Kernels below version 3.17 do not support the memfd_create syscall for creating temporary anonymous files. For those kernels we have to manually create a temporary file and delete it.

Diff Detail

Repository

rB Blender

Branch

wl_tmpfile

Build Status

Buildable 15809
Build 15809: arc lint + arc unit

Event Timeline

Christian Rauch (christian.rauch) requested review of this revision.Jul 13 2021, 1:04 AM

Christian Rauch (christian.rauch) created this revision.

Harbormaster completed remote builds in B15768: Diff 39440.Jul 13 2021, 1:04 AM

code format

Harbormaster completed remote builds in B15769: Diff 39441.Jul 13 2021, 1:14 AM

Brecht Van Lommel (brecht) requested changes to this revision.Jul 13 2021, 1:59 PM

Brecht Van Lommel (brecht) added inline comments.

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	Not sure it's worth having Linux-specific code at all, especially if we want to have this running on BSDs as well eventually.
1811	`getenv("XDG_RUNTIME_DIR")` can return `NULL`, needs to be checked.
1836–1837	Handle `mmap` failure, and close `fd` in that case.

This revision now requires changes to proceed.Jul 13 2021, 1:59 PM

Christian Rauch (christian.rauch) marked an inline comment as done.Jul 13 2021, 2:13 PM

Christian Rauch (christian.rauch) added inline comments.

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	I don't think it is worth bothering about BSD until it is seriously considered to replace X11 for them and there is at least one distribution that makes use of Wayland by default. Further to this, I have no way (and interest) in testing this on BSD. Someone else has to provide the patches and test this on BSD with Wayland.

Brecht Van Lommel (brecht) added inline comments.Jul 13 2021, 3:33 PM

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	Not expecting anyone to test this on BSD soon. But I just don't see the benefit in keeping the Linux-specific code when we now have a portable alternative.

Christian Rauch (christian.rauch) marked 2 inline comments as done.Jul 13 2021, 3:45 PM

Christian Rauch (christian.rauch) added inline comments.

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	This `mkostemp` + `unlink` is just a workaround, not identical behaviour. From https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/4: This (so-far) Linux-only API lets users create file descriptors purely in memory, without any backing file on the filesystem and the race condition which could ensue when unlink()ing it. It is Linux specific API, but it was created for a reason. The `HAVE_MEMFD_CREATE` solution in this pull request is actually a much better (portable) solution compared to my kernel version comparison. I am going to use this one too.

Christian Rauch (christian.rauch) marked an inline comment as done.Jul 13 2021, 3:49 PM

Christian Rauch (christian.rauch) added inline comments.

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	I cannot change my comment (and I cannot preview the formatting), but this is the fixed citation from the PR that justifies the use of memfd_create: This (so-far) Linux-only API lets users create file descriptors purely in memory, without any backing file on the filesystem and the race condition which could ensue when unlink()ing it.

Christian Rauch (christian.rauch) added inline comments.Jul 13 2021, 3:51 PM

intern/ghost/intern/GHOST_SystemWayland.cpp
1807	Ok, one last try: This (so-far) Linux-only API lets users create file descriptors purely in memory, without any backing file on the filesystem and the race condition which could ensue when unlink()ing it. I really don't like this Blender review system :-)