On Thu, Jun 09, 2022 at 11:53:20AM -0400, Matt Barry wrote:
> On Wed, 2022-06-08 at 11:59 +0200, Marc Haber wrote:
> > On Wed, Jun 08, 2022 at 12:34:14AM -0400, Matt Barry wrote:
> > > tags -1 + confirmed patch
> > > thanks
> >
> > How about zstd and the other hip compressors?
>
> Heh. I was thinking about whether to bother with this one. A couple
> of factors:
>
> * adding zstd in the same fashion will take ~ 2 minutes
> * there are, imo, no additional algorithms worth considering, so it
> isn't a bottomless well of feature requests
> * I guess the ideal for users would be a config item that controls the
> order of selection:
>
> BACKUP_COMPRESS=xz gz zstd # eg. would never try bzip2
>
> I can't imagine it getting more complicated than that..
Currently, the code looks like we are choosing the filename and the
method of compression: if bzip2 exists, we use that. Otherwise, if gzip
exists, we use that. Thankfully, we never documented this precedence,
our docs just say that the backup file is called
username.tar(.gz|.bz2).
Christoph suggested using tar's --auto-compress option which
automatically chooses the compress program depeding on the target file's
suffix.
How about doing the following:
- we introduce a new option --backup-suffix, accepting things like
".bz2" or "xz"
- we use that to generate the target file name, adding a period if the
input doesnt start with one
- use tar --auto-compress to create the file
Unfortunately, if tar doesnt recognize the suffix, it'll happily
generate foo.tar.baz as a regular tar archive. Otoh, if a compressor is
selected that is not installed, tar will give a 127 exit code.
I'd recommend the following:
- invoke tar --create --auto-compress --file /tmp/foo.tar.suffix
--directory / usr/sbin/deluser
- if exit code 127 (compressor known, but not installed):
- print diagnostic
- set suffix to ".gz" (gzip is essential and guaranteed to exist)
- if exit code != 127
- invoke tar --create --file /tmp/foo.tar
--directory / usr/sbin/deluser
- check whether foo.tar and foo.tar.sufffix are identical (that
happens when the tar file suffix does not match a known compressor)
- if identical (unknown compressor given)
- print diagnostic
- set suffix to ".gz"
If there is any better way to find out whether tar has actually printed
a compressed file without creating more dependencies, please, use that.
Greetings
Marc
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