Date: Wed, 14 Jan 2004 12:42:17 -0800 From: Tim Kientzle <kientzle@acm.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: freebsd-arch@freebsd.org Subject: Re: Request for Comments: libarchive, bsdtar Message-ID: <4005A9A9.6090503@acm.org> In-Reply-To: <20040114.131705.93652359.imp@bsdimp.com> References: <4004D445.7020205@acm.org> <Pine.NEB.3.96L.1040114142135.49872F-100000@fledge.watson.org> <20040114.131705.93652359.imp@bsdimp.com>
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M. Warner Losh wrote:
> In message: <Pine.NEB.3.96L.1040114142135.49872F-100000@fledge.watson.org>
> Robert Watson <rwatson@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);
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