tail: update README

* add summary of implemented/missing features
* add summary of gnu test suite results

src/uu/tail/README.md

@@ -1,28 +1,91 @@
+<!-- spell-checker:ignore markdownlint ; (libs) kqueue -->
+
 # Notes / ToDO
 
 ## Missing features
 
-The `-F` flag (same as `--follow=name --retry`) has very good support on Linux (inotify backend),
-works good enough on macOS/BSD (kqueue backend) with some minor tests not working,
-and is fully untested on Windows.
+* `--max-unchanged-stats`
+* The current implementation doesn't follow stdin on non-unix platforms
+* check whether process p is alive at least every number of seconds (relevant for `--pid`)
+
+Note:
+There's a stub for `--max-unchanged-stats` so GNU tests using it can run, however this flag has no functionality yet.
+
+### Platform support for `--follow`
+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 how kqueue works compared to inotify.
+Windows support is there in theory due to support by the notify-crate, however it's completely untested.
 
 ### Flags with features
 
-- [x] fast poll := '-s.1 --max-unchanged-stats=1'
+- [x] fast poll := `-s.1 --max-unchanged-stats=1`
     - [x] sub-second sleep interval e.g. `-s.1`
     - [ ] `--max-unchanged-stats` (only meaningful with `--follow=name` `---disable-inotify`)
+- [x] `--follow=name`
+- [x] `--retry`
+- [x] `-F` (same as `--follow=name` `--retry`)
 - [x] `---disable-inotify` (three hyphens is correct)
-- [x] `--follow=name'
-- [x] `--retry'
-- [x] `-F' (same as `--follow=name` `--retry`)
+- [x] `---presume-input-pipe` (three hyphens is correct)
 
-### Others
-
-- [ ] The current implementation doesn't follow stdin in non-unix platforms
-- [ ] Since the current implementation uses a crate for polling, these flags are too complex to implement:
-    - [ ] `--max-unchanged-stats`
-    - [ ] check whether process p is alive at least every number of seconds (relevant for `--pid`)
+Note:
+`---disable-inotify` means to use polling instead of inotify,
+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.
+* 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`
+
+# GNU tests results
+
+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-resourced.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 seperate thread. If the GNU test would use `strace -f` this issue could be resolved.
+
+## Testsuite summary for GNU coreutils 9.1.8-e08752:
+
+### PASS:
+tail-2/F-headers.sh
+tail-2/F-vs-missing.sh
+tail-2/append-only.sh # skipped test: must be run as root
+tail-2/assert-2.sh
+tail-2/assert.sh
+tail-2/big-4gb.sh
+tail-2/descriptor-vs-rename.sh
+tail-2/end-of-device.sh # skipped test: must be run as root
+tail-2/flush-initial.sh
+tail-2/follow-name.sh
+tail-2/inotify-dir-recreate.sh
+tail-2/inotify-hash-abuse.sh
+tail-2/inotify-hash-abuse2.sh
+tail-2/inotify-only-regular.sh
+tail-2/inotify-rotate.sh
+tail-2/overlay-headers.sh
+tail-2/pid.sh
+tail-2/pipe-f2.sh
+tail-2/proc-ksyms.sh
+tail-2/start-middle.sh
+tail-2/tail-c.sh
+tail-2/tail-n0f.sh
+tail-2/truncate.sh
+
+### SKIP:
+tail-2/inotify-race.sh # skipped test: breakpoint not hit
+tail-2/inotify-race2.sh # skipped test: breakpoint not hit
+tail-2/pipe-f.sh # skipped test: trapping SIGPIPE is not supported
+
+### FAIL:
+misc/tail.pl
+tail-2/F-vs-rename.sh
+tail-2/follow-stdin.sh
+tail-2/retry.sh
+tail-2/symlink.sh
+tail-2/wait.sh
+
+### ERROR:
+tail-2/inotify-rotate-resources.sh

src/uu/tail/src/tail.rs

@@ -189,13 +189,13 @@ impl Settings {
 
         let mut starts_with_plus = false;
         let mode_and_beginning = if let Some(arg) = matches.value_of(options::BYTES) {
-            starts_with_plus = arg.starts_with("+");
+            starts_with_plus = arg.starts_with('+');
             match parse_num(arg) {
                 Ok((n, beginning)) => (FilterMode::Bytes(n), beginning),
                 Err(e) => return Err(format!("invalid number of bytes: {}", e)),
             }
         } else if let Some(arg) = matches.value_of(options::LINES) {
-            starts_with_plus = arg.starts_with("+");
+            starts_with_plus = arg.starts_with('+');
             match parse_num(arg) {
                 Ok((n, beginning)) => (FilterMode::Lines(n, b'\n'), beginning),
                 Err(e) => return Err(format!("invalid number of lines: {}", e)),