symbolic link to fifo : rmlint hangs in rm_sys_open from rm_util_is_nonstripped #792

I recently used rmlint to deduplicate a decade or so of backup/archive files. It kept getting stuck (completely hanging, no disk or CPU activity, no error message) on what I eventually tracked down to be a (duplicate) symbolic link to a fifo/pipe file.

I asked rmlint only to find duplicate files, yet it also checked for non-stripped ELFs. The link that it opened was a link, not a file, despite the "-T df" option. (I think that lstat() could detect this.) Also, the link was to a file on another filesystem, even though the -x flag indicates that rmlint should stick to a single filesystem. (Though it may have no way to know this before stat'ing the destination file.)

I compiled with 'scons DEBUG=1' and added fprintf to the inline function rm_sys_open as well as before every call to rm_sys_open.

$ ./rmlint/rmlint --version
version 2.10.3 compiled: Aug 10 2026 at [16:50:27] "Ludicrous Lemur" (rev b311f38)
compiled with: +mounts +nonstripped +fiemap +sha512 +bigfiles +intl +replay +xattr +btrfs-support

rmlint was written by Christopher Pahl and Daniel Thomas.
The code at https://github.com/sahib/rmlint is licensed under the terms of the GPLv3.
$

$ ./rmlint/rmlint -x -T df -S m -o sh:rmlint.sh -c sh:hardlink ./foobar/
is_nonstripped: rm_sys_open /mnt/gdrive/ashmansk/foobar/simtest_output.fifo
rm_sys_open: 0 /mnt/gdrive/ashmansk/foobar/simtest_output.fifo
[hangs up here, no further CPU or disk activity, no error message]
^\Quit (core dumped)
[ble: exit 131]
$

$ ls -lR ./foobar/
./foobar/:
total 4
drwxrwxr-x 2 ashmansk ashmansk 4096 Aug 10 16:39 subdir
lrwxrwxrwx 1 ashmansk ashmansk 38 Jul 18 2016 simtest_input.fifo -> /data/ashmansk/temp/simtest_input.fifo
lrwxrwxrwx 1 ashmansk ashmansk 39 Jul 18 2016 simtest_output.fifo -> /data/ashmansk/temp/simtest_output.fifo

./foobar/subdir:
total 0
lrwxrwxrwx 1 ashmansk ashmansk 38 Jul 18 2016 simtest_input.fifo -> /data/ashmansk/temp/simtest_input.fifo
lrwxrwxrwx 1 ashmansk ashmansk 39 Jul 18 2016 simtest_output.fifo -> /data/ashmansk/temp/simtest_output.fifo
$

$ ls -l /data/ashmansk/temp/*.fifo
prw-rw-r-- 1 ashmansk ashmansk 0 Jul 19 2016 /data/ashmansk/temp/simtest_input.fifo
prw-rw-r-- 1 ashmansk ashmansk 0 Jul 19 2016 /data/ashmansk/temp/simtest_output.fifo
$

It appears that even opening the fifo, without reading, is enough to block:

$ python3
Python 3.14.4 (main, Jun 18 2026, 14:25:02) [GCC 15.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

fp = open("foobar/simtest_output.fifo", "r")
[hangs]
^\Quit (core dumped)
[ble: exit 131]
$

$ python3
Python 3.14.4 (main, Jun 18 2026, 14:25:02) [GCC 15.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

open("/data/ashmansk/temp/simtest_output.fifo")
^\Quit (core dumped) python3
[ble: exit 131]
$

But it is possible to lstat the link, to see that it is a link, or to stat the link, to see that the link target is a fifo:

$ python3
Python 3.14.4 (main, Jun 18 2026, 14:25:02) [GCC 15.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

import os
os.lstat("foobar/simtest_output.fifo")
os.stat_result(st_mode=41471, st_ino=78066383, st_dev=2113, st_nlink=1, st_uid=1001, st_gid=1001, st_size=39, st_atime=1786394119, st_mtime=1468858321, st_ctime=1785531874)
os.stat("foobar/simtest_output.fifo")
os.stat_result(st_mode=4532, st_ino=1514250, st_dev=48, st_nlink=1, st_uid=1001, st_gid=1001, st_size=0, st_atime=1578709601, st_mtime=1468959945, st_ctime=1644101480)
import stat
stat.S_ISFIFO(os.stat("foobar/simtest_output.fifo").st_mode)
True
^D
$

I think there may be several questions here about the intended rmlint behavior:

• If one enters "-T df", should a check using lstat() reject symbolic links before trying to rm_sys_open them?
• Before rm_sys_open opens a file, should it first use stat() to check that it (or its link target) is not a fifo?
• If "-x" is applied, should "rm_lint_open" be preceded by checking the stat() result for device number, to reject links to different filesystems?

Please let me know if you need further information. I didn't dig deeply enough through the code to feel confident submitting a PR.

-Bill