On Jun 12, 2019, at 12:15 PM, Brian Murray <br...@ubuntu.com> wrote: > > On Wed, Jun 12, 2019 at 10:32:22AM -0700, Brian Murray wrote: >> On Mon, Jun 10, 2019 at 05:49:49PM -0600, Andreas Dilger wrote: >>> On Jun 3, 2019, at 2:27 PM, Brian Murray <br...@ubuntu.com> wrote: >>>> >>>> When enabling extended attribute support in a tar file (--xattrs) all >>>> extended attributes are stored in the archive, however when the same >>>> archive >>>> is extracted only the user.* extended attributes are extracted. To have all >>>> the extended attributes read and applied on extraction one must also use >>>> the >>>> '--xattrs-include=*' option. I find this behavior surprising and >>>> especially so >>>> given that the documentation indicates that "By default, when `--xattr' is >>>> used, all names are stored in the archive (or extracted, if using >>>> `--extract')"[1]. >>>> >>>> I'm happy to help working on resolving this issue but it isn't clear to me >>>> whether the program or the documentation is incorrect. I've read some of >>>> this >>>> mailing list's archive but didn't find an explanation as to why >>>> restoration of >>>> only 'user.*' extended attributes would not be a bug[2]. >>>> >>>> [1] https://www.gnu.org/software/tar/manual/tar.html#SEC70 >>>> [2] Which I reported here https://savannah.gnu.org/bugs/index.php?56421 >>> >>> As Pavel mentioned, it isn't necessarily safe/correct to extract all xattrs, >>> especially in cross-platform usage. However, it *does* make sense to save >>> all of the xattrs, since it is then possible to extract whichever ones that >>> are useful. If the xattrs aren't saved at time of archive creation, they >>> may be permanently lost. >> >> Thanks for the information Pavel and Andreas. Given what you've said >> I've created a couple of patches, one for the documentation change and >> one adding a comment to xattrs.c which clarifies why only user.* >> extended attributes are extracted by default. > > I'd forgotten about updating the man page for tar, attached you'll find > a patch for that too. >
> diff --git a/doc/tar.1 b/doc/tar.1 > index 18136cf..1bb9d30 100644 > --- a/doc/tar.1 > +++ b/doc/tar.1 > @@ -604,7 +604,9 @@ Enable SELinux context support. > Disable SELinux context support. > .TP > .B \-\-xattrs > -Enable extended attributes support. > +Enable extended attributes support. When creating an archive > +\fB\-\-xattrs\-include\fR defaults to \fB'*'\fR and when extracing an > +archive \fB\-\-xattrs\-include\fR defaults to \fB'^user.*'\fR. Since the man page is the primary source of information for most users, I'd expand this a bit, like "When creating an archive, --xattrs-include defaults to '*' so that \fBall\fR xattrs are saved into the archive so that any of them \fImay\fR be extracted later, but when extracting an archive --xattrs-include defaults to '^user.*' to avoid extracting system-specific xattrs that are not portable, and may cause errors on some systems. Multiple '--xattrs-include` options can be specified. While ACLs and SELinux labels may be stored on-disk in xattrs, they are controlled with the '--acl' and '--selinux' options." Cheers, Andreas
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