tempfile-fast

(Slightly) faster temporary files on Linux

On "recent" Linux (~2014+), filesystems support a new type of unnamed, persistable temporary file.

The excellent tempfile crate supports two types of temporary files:

• unnamed temporary files, which are secure and fast, but which can never be written into real the filesystem.
• named temporary files, which have some theoretical security risks and performance problems, but you must use if you ever want to write the data into the real filesystem efficiently.

It does not, however, expose unnamed (secure, fast), persistable (convenient) files. This crate does.

The performance, or even the series of operations, may be identical for your use-case: tempfile has changed significantly since this code was written.

On non-modern-Linux, this crate falls back to using tempfile's NamedTemporaryFile directly.

"recent" Linux

Support for O_TMPFILE was added to:

• Linux 3.11: ext2, ext3, ext4, UDF, Minix, shmem.
• Linux 3.15: xfs
• Linux 3.16: btrfs, f2fs
• Linux 4.9: ubifs

Some distros, with release dates, End of Life dates, and kernel versions:

• RHEL 7 (Jun 2014 - Jun 2024): 3.10
• Debian Jessie (Apr 2015 - Apr 2020): 3.16
• OpenSUSE Leap 42.1 (Nov 2015 - May 2017): 4.1
• Ubuntu 14.04.5 (Aug 2016 - Apr 2019): 4.4
• Debian Stretch (Jun 2017 - Jul 2020): 4.9
• Ubuntu 16.04.2 (Apr 2016 - Apr 2021): 4.15
• RHEL 8 (May 2019 - May 2029): 4.18
• Debian Buster (July 2019 - Sep 2022): 4.19

i.e. since about 2024, everything in support, even for RHEL, will likely be new enough.

Upstreaming

An alternative implementation, ramming this into NamedTemporaryFile, was discussed in a pull-request. This was the result.