Unexpected behavior of 'tail --follow=name' on special file via symlink

[Glenn Golden]

Not sure if this is a bug report, a feature request, or just a case of wrong
expectation on my part regarding the behavior of "tail --follow=name" when
the target is a special file (via a symlink).  Perhaps what I'm trying to do
is unreasonable and shouldn't really be expected to work.

In any case, any suggestions as to how to accomplish the desired goal would be
appreciated, even if by entirely different means than using tail per se.

Detailed description follows; version info at the end.

Thanks,

- Glenn



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Background:

 I'm working with a USB device that writes debug info to a /dev/ttyACM
 interface which I then wish to observe continuously using tail(1) with the
 --follow=name option.  It is desirable for the tail process to gracefully
 survive a reboot of the target USB device, so that upon reboot, tail will
 continue to display the device's "new" debug stream.

 To accomplish this, a udev rule is defined which creates a consistent
 symlink name pointing to the device's ACM interface (let's call that symlink
 "/dev/ttyMYDEV").  So, upon reboot of the target USB device, udev duly
 re-points /dev/ttyMYDEV to the appropriate (kernel-named) /dev/ttyACMn
 interface presented by the device when it reincarnates after its reboot.

 As far as I'm able to tell, the udev rule does seem to accomplish that
 symlink creation correctly.

----------------------------------------------------------------------------
Expectation:

 Given the above, my expectation was that

   $ tail --follow=name /dev/ttyMYDEV"

 would handle the above-described situation gracefully upon reboot of the
 target device, similar to its behavior when using --follow=name to follow
 an on-the-fly re-created logfile having the same name as the original but
 a new file descriptor (e.g. due to log rotation).

 In other words, what I expected to see was something like this:

   
   $ tail --follow=name /dev/ttyMYDEV

   Debug output line 1
   Debug output line 2
         .
         .
         .
   Debug output line n
   Debug output line n+1
   Debug output line n+2

   (==> target USB device is rebooted here <==)

   tail: '/dev/ttyMYDEV' has been replaced;  following new file

   Debug output line 1          # First line of "new" debug output
   Debug output line 2          # Second line of "new" debug output
         .
         .
         .

----------------------------------------------------------------------------
Observed behavior:

 Instead of the above, what is actually observed is this:

   $ tail --follow=name /dev/ttyMYDEV

   Debug output line 1
   Debug output line 2
         .
         .
         .
   Debug output line n
   Debug output line n+1
   Debug output line n+2

   (==> target USB device is rebooted here <==)

   tail: '/dev/ttyMYDEV' has been replaced;  following new file
   tail: /dev/ttyMYDEV: cannot seek to offset 0: Illegal seek


So... is this an inevitable consequence of trying to follow an un-seekable
special file?  Or could it possibly be handled in some fancy way so as to
provide the desired behavior?

----------------------------------------------------------------------------
Version info:
 GNU coreutils 9.1, Arch linux, kernel 5.15.87-1-lts, commodity x86_64 laptop.
============================================================================