Re: Request for Comments: libarchive, bsdtar

From: Tim Kientzle (kientzle_at_acm.org)
Date: 01/14/04

  • Next message: Poul-Henning Kamp: "Re: Request for Comments: libarchive, bsdtar" 
    Date: Wed, 14 Jan 2004 12:42:17 -0800
To: "M. Warner Losh" <imp@bsdimp.com>

    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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  • Next message: Poul-Henning Kamp: "Re: Request for Comments: libarchive, bsdtar"

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