Notes / ToDO

Missing features

• --max-unchanged-stats

Note: There's a stub for --max-unchanged-stats so GNU test-suite checks using it can run, however this flag has no functionality yet.

Platform support for --follow and --retry

The --follow=descriptor, --follow=name and --retry flags have very good support on Linux (inotify backend). They work good enough on macOS/BSD (kqueue backend) with some tests failing due to differences of how kqueue works compared to inotify. Windows support is there in theory due to ReadDirectoryChanges support by the notify-crate, however these flags are completely untested on Windows.

Note: The undocumented ---disable-inotify flag is used to disable the inotify backend to test polling. However inotify is a Linux only backend and polling is now supported also for the other backends. Because of this, disable-inotify is now an alias to the new and more versatile flag name: --use-polling.

Possible optimizations

• Don't read the whole file if not using -f and input is regular file. Read in chunks from the end going backwards, reading each individual chunk forward.
• Reduce number of system calls to e.g. fstat
• Improve resource management by adding more system calls to inotify_rm_watch when appropriate.

GNU test-suite results (9.1.8-e08752)

The functionality for the test "gnu/tests/tail-2/follow-stdin.sh" is implemented. It fails because it is provoking closing a file descriptor with tail -f <&- and as part of a workaround, Rust's stdlib reopens closed FDs as /dev/null which means uu_tail cannot detect this. See also, e.g. the discussion at: https://github.com/uutils/coreutils/issues/2873

The functionality for the test "gnu/tests/tail-2/inotify-rotate-resources.sh" is implemented. It fails with an error because it is using strace to look for calls to inotify_add_watch and inotify_rm_watch, however in uu_tail these system calls are invoked from a separate thread. If the GNU test would follow threads, i.e. use strace -f, this issue could be resolved.

There are 5 tests which are fixed but do not (always) pass the test suite if it's run inside the CI. The reason for this is probably related to load/scheduling on the CI test VM. The tests in question are:

• tail-2/F-vs-rename.sh
• tail-2/follow-name.sh
• tail-2/inotify-rotate.sh
• tail-2/overlay-headers.sh
• tail-2/retry.sh