/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <stdio.h>
#include <strings.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/mntent.h>
#include <unistd.h>

/*
 * This program aids the Solaris 10 patch tools (specifically
 * /usr/lib/patch/patch_common_lib) in DAP patching.
 *
 * Whenever the patch tools replace a critical system component (e.g.,
 * /lib/libc.so.1), they move the old component to a temporary location,
 * move the new component to where the old component was, and establish
 * an overlay mount of the old component on top of the new component.
 * The patch tools do this with a shell script; consequently, the three
 * operations occur in three processes.
 *
 * This doesn't work inside Solaris 10 Containers (S10Cs).  Suppose the
 * patch tools need to replace /lib/libc.so.1.  The tools will move the old
 * libc.so.1 to a temporary location.  But when they try to move the new
 * libc.so.1, they fork a mv(1) process, which loads the solaris10 brand's
 * emulation library.  The emulation library will try to load the zone's
 * libc.so.1, but the library no longer exists; consequently, the emulation
 * library aborts and the zone's users won't be able to start any processes.
 *
 * This program solves the problem by combining the move and mount operations
 * into a single process.  The emulation library will already have loaded
 * libc.so.1 for the process by the time the process starts to replace
 * libc.so.1.
 *
 * This program takes six parameters that correspond to six variables within
 * /usr/lib/patch/patch_common_lib:InstallSafemodeObject():
 *
 *      argv[1] - dstActual (the path to the file that will be replaced)
 *      argv[2] - tmp_file (the temporary location to which the file will be
 *              moved)
 *      argv[3] - tmpDst (the path to the replacement file)
 *      argv[4] - tmpFile (the path to a temporary copy of the running system's
 *              version of the file being replaced; the source [special] of
 *              the overlay mount)
 *      argv[5] - cksumTmpDst (checksum of the file represented by tmpDst)
 *      argv[6] - cksumTmpFile (checksum of the file represented by tmpFile)
 *
 * NOTE: This program will only establish an overlay mount if argv[4] or argv[5]
 * is emtpy or if argv[4] and argv[5] differ.
 *
 * This program returns zero when it succeeds.  Non-negative values indicate
 * failure.
 */
int
main(int argc, char **argv)
{
        struct stat statbuf;
        char mntoptions[MAX_MNTOPT_STR];

        /*
         * Check the number of arguments that were passed to s10_replacefile.
         */
        if (argc != 7) {
                (void) fprintf(stderr, "Usage: %s dstActual tmp_file tmpDst "
                    "tmpFile cksumTmpDst cksumTmpFile\n", argv[0]);
                return (1);
        }

        /*
         * Move the destination file (dstActual) out of the way and move the
         * new file (tmpDst) into its place.
         *
         * NOTE: s10_replacefile won't print error messages here because
         * the Solaris 10 patch tools will.
         */
        if (rename(argv[1], argv[2]) != 0)
                return (2);
        if (rename(argv[3], argv[1]) != 0)
                return (3);

        /*
         * If there was a lofs mount on dstActual (which we just moved), then
         * s10_replacefile should reestablish the lofs mount.  A lofs mount
         * existed if tmpFile exists.
         */
        if (stat(argv[4], &statbuf) == 0 && (statbuf.st_mode & S_IFREG)) {
                /*
                 * Create a lofs overlay mount only if the checksums of the
                 * old file at dstActual and the new file at dstActual differ.
                 */
                if (argv[5][0] == '\0' || argv[6][0] == '\0' ||
                    strcmp(argv[5], argv[6]) != 0) {
                        mntoptions[0] = '\0';
                        if (mount(argv[4], argv[1], MS_OVERLAY | MS_OPTIONSTR,
                            MNTTYPE_LOFS, NULL, 0, mntoptions,
                            sizeof (mntoptions)) != 0) {
                                /*
                                 * Although the patch tools will print error
                                 * messages, the tools won't know that
                                 * s10_replacefile failed to establish an
                                 * overlay mount.  Printing an error message
                                 * here clarifies the problem for the user.
                                 */
                                (void) fprintf(stderr, "ERROR: Failed to "
                                    "overlay mount %s onto %s\n", argv[4],
                                    argv[1]);
                                return (4);
                        }
                } else {
                        /*
                         * dstActual does not need an overlay mount.  Delete
                         * tmpFile.
                         */
                        (void) unlink(argv[4]);
                }
        }
        return (0);
}