Request for Comments: libarchive, bsdtar

[Tim Kientzle]

M. Warner Losh wrote:
> In message: <Pine.NEB.3.96L.1040114142135.49872F-100000 at fledge.watson.org>
>             Robert Watson <rwatson at freebsd.org> writes:
> : I know NetBSD has a neat tool to create file systems from userspace
> : without privilege, but my understanding is that it has to pull in a lot of
> : code from the kernel in fairly messy ways.  Since tar files are a well
> : supported portable format... :-)
> 
> The problem then reduces to needing to be able to create the tar file
> with ownership/permissions different than is in the unpriv'd build
> tree.  Generation of this list, as well as getting tar/whatever to
> honor it are interesting problems.

Not all that interesting, really.  ;-)

For example, the following simple C program uses
libarchive to read an archive from stdin, and write a new
ustar/gzip archive to stdout with all entries owned by 'root'.
You just create the archive as usual and then feed it through
this filter to create a new archive with the proper
ownership/permissions.  The same technique can be used add
entries to an archive, remove entries from an archive, rename
archive entries, convert archive formats, etc.


struct archive *in;
struct archive *out;
struct archive_entry *entry;

/* Read an archive from stdin: format/compression
    will be auto-detected. */
in = archive_read_new();
archive_read_support_format_all(in);
archive_read_support_compression_all(in);
archive_read_open_file(in, NULL);  /* NULL == stdin */

/* Write a ustar/gzip archive to stdout. */
out = archive_write_new();
archive_write_set_compression_gzip(out);
archive_write_set_format_ustar(out);
archive_write_open_file(out, NULL); /* NULL == stdout */

/* Copy entries over, doing any necessary editing */
while (archive_read_next_header(in, &entry) == ARCHIVE_READ_OK) {
     /* Edit the entry as appropriate */
     archive_entry_set_uid(entry, 0);
     archive_entry_set_uname(entry, "root");
     /* Write a header to the output archive */
     archive_write_header(out, entry);
     /* TODO: XXX Copy data to output archive XXX */
}
/* All done */
archive_write_finish(out);
archive_read_finish(in);