dissect: add small "systemd-dissect" tool as wrapper around dissect-image.c

This adds a small tool that may be used to look into OS images, and mount them
to any place. This is mostly a friendlier version of test-dissect-image.c. I am
not sure this should really become a proper command of systemd, hence for now
do not install it into bindir, but simply libexecdir.

This tool is already pretty useful since you can mount image files with it,
honouring the various partitions correctly. I figure this is going to become
more interesting if the dissctor learns luks and verity support.

6 files changed, 234 insertions, 3 deletions

diff --git a/.gitignore b/.gitignore
index 405b07ef4d..baa975d813 100644
--- a/.gitignore
+++ b/.gitignore
@@ -67,6 +67,7 @@
 /systemd-debug-generator
 /systemd-delta
 /systemd-detect-virt
+/systemd-dissect
 /systemd-escape
 /systemd-export
 /systemd-firstboot
diff --git a/Makefile.am b/Makefile.am
index c47a07a1f0..c6adf3a65c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -404,6 +404,11 @@ rootlibexec_PROGRAMS = \
 	systemd-socket-proxyd \
 	systemd-update-done
 
+if HAVE_BLKID
+rootlibexec_PROGRAMS += \
+	systemd-dissect
+endif
+
 if HAVE_UTMP
 rootlibexec_PROGRAMS += \
 	systemd-update-utmp
@@ -3074,6 +3079,13 @@ systemd_notify_LDADD = \
 	libsystemd-shared.la
 
 # ------------------------------------------------------------------------------
+systemd_dissect_SOURCES = \
+	src/dissect/dissect.c
+
+systemd_dissect_LDADD = \
+	libsystemd-shared.la
+
+# ------------------------------------------------------------------------------
 systemd_path_SOURCES = \
 	src/path/path.c
 
diff --git a/src/dissect/Makefile b/src/dissect/Makefile
new file mode 120000
index 0000000000..d0b0e8e008
--- /dev/null
+++ b/src/dissect/Makefile
@@ -0,0 +1 @@
+../Makefile
\ No newline at end of file
diff --git a/src/dissect/dissect.c b/src/dissect/dissect.c
new file mode 100644
index 0000000000..93ece05948
--- /dev/null
+++ b/src/dissect/dissect.c
@@ -0,0 +1,206 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <getopt.h>
+
+#include "architecture.h"
+#include "dissect-image.h"
+#include "log.h"
+#include "loop-util.h"
+#include "string-util.h"
+#include "util.h"
+
+static enum {
+        ACTION_DISSECT,
+        ACTION_MOUNT,
+} arg_action = ACTION_DISSECT;
+static const char *arg_image = NULL;
+static const char *arg_path = NULL;
+static bool arg_read_only = false;
+
+static void help(void) {
+        printf("%s [OPTIONS...] IMAGE\n"
+               "%s [OPTIONS...] --mount IMAGE PATH\n"
+               "Dissect a file system OS image.\n\n"
+               "  -h --help            Show this help\n"
+               "     --version         Show package version\n"
+               "  -m --mount           Mount the image to the specified directory\n"
+               "  -r --read-only       Mount read-only\n",
+               program_invocation_short_name,
+               program_invocation_short_name);
+}
+
+static int parse_argv(int argc, char *argv[]) {
+
+        enum {
+                ARG_VERSION = 0x100,
+        };
+
+        static const struct option options[] = {
+                { "help",      no_argument,       NULL, 'h'           },
+                { "version",   no_argument,       NULL, ARG_VERSION   },
+                { "mount",     no_argument,       NULL, 'm'           },
+                { "read-only", no_argument,       NULL, 'r'           },
+                {}
+        };
+
+        int c;
+
+        assert(argc >= 0);
+        assert(argv);
+
+        while ((c = getopt_long(argc, argv, "hmr", options, NULL)) >= 0) {
+
+                switch (c) {
+
+                case 'h':
+                        help();
+                        return 0;
+
+                case ARG_VERSION:
+                        return version();
+
+                case 'm':
+                        arg_action = ACTION_MOUNT;
+                        break;
+
+                case 'r':
+                        arg_read_only = true;
+                        break;
+
+                case '?':
+                        return -EINVAL;
+
+                default:
+                        assert_not_reached("Unhandled option");
+                }
+
+        }
+
+        switch (arg_action) {
+
+        case ACTION_DISSECT:
+                if (optind + 1 != argc) {
+                        log_error("Expected a file path as only argument.");
+                        return -EINVAL;
+                }
+
+                arg_image = argv[optind];
+                arg_read_only = true;
+                break;
+
+        case ACTION_MOUNT:
+                if (optind + 2 != argc) {
+                        log_error("Expected a file path and mount point path as only arguments.");
+                        return -EINVAL;
+                }
+
+                arg_image = argv[optind];
+                arg_path = argv[optind + 1];
+                break;
+
+        default:
+                assert_not_reached("Unknown action.");
+        }
+
+        return 1;
+}
+
+int main(int argc, char *argv[]) {
+        _cleanup_(loop_device_unrefp) LoopDevice *d = NULL;
+        _cleanup_(dissected_image_unrefp) DissectedImage *m = NULL;
+        int r;
+
+        log_parse_environment();
+        log_open();
+
+        r = parse_argv(argc, argv);
+        if (r <= 0)
+                goto finish;
+
+        r = loop_device_make_by_path(arg_image, arg_read_only ? O_RDONLY : O_RDWR, &d);
+        if (r < 0) {
+                log_error_errno(r, "Failed to set up loopback device: %m");
+                goto finish;
+        }
+
+        r = dissect_image(d->fd, &m);
+        if (r == -ENOPKG) {
+                log_error_errno(r, "Couldn't identify a suitable partition table or file system in %s.", arg_image);
+                goto finish;
+        }
+        if (r < 0) {
+                log_error_errno(r, "Failed to dissect image: %m");
+                goto finish;
+        }
+
+        switch (arg_action) {
+
+        case ACTION_DISSECT: {
+                unsigned i;
+
+                for (i = 0; i < _PARTITION_DESIGNATOR_MAX; i++) {
+                        DissectedPartition *p = m->partitions + i;
+
+                        if (!p->found)
+                                continue;
+
+                        printf("Found %s '%s' partition",
+                               p->rw ? "writable" : "read-only",
+                               partition_designator_to_string(i));
+
+                        if (p->fstype)
+                                printf(" of type %s", p->fstype);
+
+                        if (p->architecture != _ARCHITECTURE_INVALID)
+                                printf(" for %s", architecture_to_string(p->architecture));
+
+                        if (p->partno >= 0)
+                                printf(" on partition #%i", p->partno);
+
+                        if (p->node)
+                                printf(" (%s)", p->node);
+
+                        putchar('\n');
+                }
+
+                break;
+        }
+
+        case ACTION_MOUNT:
+                r = dissected_image_mount(m, arg_path,
+                                          (arg_read_only ? DISSECTED_IMAGE_READ_ONLY : 0) |
+                                          DISSECTED_IMAGE_DISCARD_ON_LOOP);
+                if (r < 0) {
+                        log_error_errno(r, "Failed to mount image: %m");
+                        goto finish;
+                }
+
+                loop_device_relinquish(d);
+                break;
+
+        default:
+                assert_not_reached("Unknown action.");
+        }
+
+finish:
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+}
diff --git a/src/shared/loop-util.c b/src/shared/loop-util.c
index 8be4dbf938..047e213634 100644
--- a/src/shared/loop-util.c
+++ b/src/shared/loop-util.c
@@ -129,7 +129,7 @@ LoopDevice* loop_device_unref(LoopDevice *d) {
 
         if (d->fd >= 0) {
 
-                if (d->nr >= 0) {
+                if (d->nr >= 0 && !d->relinquished) {
                         if (ioctl(d->fd, LOOP_CLR_FD) < 0)
                                 log_debug_errno(errno, "Failed to clear loop device: %m");
 
@@ -138,7 +138,7 @@ LoopDevice* loop_device_unref(LoopDevice *d) {
                 safe_close(d->fd);
         }
 
-        if (d->nr >= 0) {
+        if (d->nr >= 0 && !d->relinquished) {
                 _cleanup_close_ int control = -1;
 
                 control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
@@ -155,3 +155,12 @@ LoopDevice* loop_device_unref(LoopDevice *d) {
 
         return NULL;
 }
+
+void loop_device_relinquish(LoopDevice *d) {
+        assert(d);
+
+        /* Don't attempt to clean up the loop device anymore from this point on. Leave the clean-ing up to the kernel
+         * itself, using the loop device "auto-clear" logic we already turned on when creating the device. */
+
+        d->relinquished = true;
+}
diff --git a/src/shared/loop-util.h b/src/shared/loop-util.h
index 5c847c4ac3..45fead5f18 100644
--- a/src/shared/loop-util.h
+++ b/src/shared/loop-util.h
@@ -29,11 +29,13 @@ struct LoopDevice {
         int fd;
         int nr;
         char *node;
+        bool relinquished;
 };
 
 int loop_device_make(int fd, int open_flags, LoopDevice **ret);
 int loop_device_make_by_path(const char *path, int open_flags, LoopDevice **ret);
 
 LoopDevice* loop_device_unref(LoopDevice *d);
-
 DEFINE_TRIVIAL_CLEANUP_FUNC(LoopDevice*, loop_device_unref);
+
+void loop_device_relinquish(LoopDevice *d);