[Bug 275465] "tail -F/f foo" doesn't show the file content when foo is truncated

From: <bugzilla-noreply_at_freebsd.org>
Date: Sun, 03 Mar 2024 11:30:48 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275465

Daniel Tameling <tamelingdaniel@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |tamelingdaniel@gmail.com

--- Comment #2 from Daniel Tameling <tamelingdaniel@gmail.com> ---
I think that the kevent in forward.c doesn't return for the truncation itself
but only after the truncation + write. At that point, the code can't figure out
whether it needs to reread the entire file. It just sees the difference in file
sizes. See for example:

$ touch test.txt                                                                
$ echo -n 123 > test.txt                                                        
$ echo -n 456789 > test.txt                                                     
$ echo -n a > test.txt                                                          
$ echo -n bcdef > test.txt

gives the output

$ tail -f test.txt                                                              
123789cdef

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