RE: [EXTERNAL] Re: New command consideration - curtail

[Wolaver, David]

On 08/11/18 09:02, Wolaver, David wrote:
> Hi all,
> 
> I have developed a command line program that I would like to have considered 
> for inclusion in a future revision of coreutils.  The name of the program is 
> "curtail".  It reads stdin and appends to an output file while ensuring that 
> the file will never exceed a specified maximum size.  The main intent is to 
> place a bound on the output of a program such that it cannot create a runaway 
> log file.  The output file is truncated (in multiple of block size) at the 
> beginning such that the output file always contains the latest output of the 
> program.
> 
> user_program | curtail -s 4M output.txt

It's a perfect name for such a command anyway :)

Does this depend on FALLOC_FL_COLLAPSE_RANGE support.
Would this command fail on file systems not supporting this?
Being block based seems a little problematic, especially considering multi-byte 
characters, but maybe that's OK.

cheers,
Pádraig

Hi Pádraig,

Thanks for spending some time to think about curtail.  I purposely omitted 
implementation details from the first post because they are irrelevant unless 
the following can be established...

1. There exists problem(s) that can be addressed by such a program (I have only 
presented one scenario)
2. Consensus that existing coreutils/scripts cannot produce the same result - 
at least not in an efficient manner
3. A solution to the problem belongs in coreutils

To answer your question.. yes FALLOC_FL_COLLAPSE_RANGE is the mechanism by 
which files are truncated in the Linux implementation.  Any OS/filesystem can 
be supported if it provides a mechanism to query block size and remove blocks 
from the beginning of a file.

Best regards,
Dave