#!/bin/sh
# ensure that tail -F doesn't leak inotify resources

# Copyright (C) 2015-2025 Free Software Foundation, Inc.

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
print_ver_ tail

# Inotify not used on remote file systems
require_local_dir_

grep '^#define HAVE_INOTIFY 1' "$CONFIG_HEADER" >/dev/null \
  || skip_ 'inotify required'

require_strace_ 'inotify_add_watch,inotify_rm_watch'

check_tail_output()
{
  local delay="$1"
  grep "$tail_re" out > /dev/null ||
    { sleep $delay; return 1; }
}

# Wait up to 25.5 seconds for grep REGEXP 'out' to succeed.
grep_timeout() { tail_re="$1" retry_delay_ check_tail_output .1 8; }

check_strace()
{
  local delay="$1"
  grep "$strace_re" strace.out > /dev/null ||
    { sleep $delay; return 1; }
}

cleanup_fail()
{
  cat out
  warn_ $1
  fail=1
}

# Terminate any background tail process
cleanup_() { kill $pid 2>/dev/null && wait $pid; }

fastpoll='-s.1 --max-unchanged-stats=1'

touch k || framework_failure_

# Note the timeout guard isn't strictly necessary here,
# however without it strace will ignore SIGTERM.
# strace does always honor SIGTERM with the -I2 option,
# though that's not available on RHEL6 for example.
timeout 180 strace -e inotify_add_watch,inotify_rm_watch -o strace.out \
  tail -F $fastpoll k >> out 2>&1 & pid=$!

reverted_to_polling_=0
for i in $(seq 2); do
    echo $i

    echo 'tailed' > k;

    # Wait for watch on (new) file
    strace_re='inotify_add_watch.*MODIFY' retry_delay_ check_strace .1 8 ||
      no_watch_=1

    # Assume this is not because we're leaking
    # (resources may already be depleted)
    # The explicit check for inotify_rm_watch should confirm that.
    grep -F 'reverting to polling' out >/dev/null && skip_ 'inotify unused'

    # Otherwise failure is unknown
    test "$no_watch_" && { cat out; framework_failure_ 'no inotify_add_watch'; }

    mv k k.tmp
    # wait for tail to detect the rename
    grep_timeout 'inaccessible' ||
      { cleanup_fail 'failed to detect rename'; break; }

    # Note we strace here rather than consuming all available watches
    # to be more efficient, but more importantly avoid depleting resources.
    # Note also available resources can currently be tuned with:
    #  sudo sysctl -w fs.inotify.max_user_watches=$smallish_number
    # However that impacts all processes for the current user, and also
    # may not be supported in future, instead being auto scaled to RAM
    # like the Linux epoll resources were.
    if test "$i" -gt 1; then
      strace_re='inotify_rm_watch' retry_delay_ check_strace .1 8 ||
        { cleanup_fail 'failed to find inotify_rm_watch syscall'; break; }
    fi

    >out && >strace.out || framework_failure_ 'failed to reset output files'
done

cleanup_

Exit $fail
