udevadm: add new "lock" verb for locking block devices

4 files changed, 403 insertions, 0 deletions

diff --git a/src/udev/meson.build b/src/udev/meson.build
index 8a2926db30..354b923291 100644
--- a/src/udev/meson.build
+++ b/src/udev/meson.build
@@ -6,6 +6,7 @@ udevadm_sources = files(
         'udevadm-control.c',
         'udevadm-hwdb.c',
         'udevadm-info.c',
+        'udevadm-lock.c',
         'udevadm-monitor.c',
         'udevadm-settle.c',
         'udevadm-test.c',
diff --git a/src/udev/udevadm-lock.c b/src/udev/udevadm-lock.c
new file mode 100644
index 0000000000..fae464704f
--- /dev/null
+++ b/src/udev/udevadm-lock.c
@@ -0,0 +1,399 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <getopt.h>
+#include <stdlib.h>
+#include <sys/file.h>
+#include <unistd.h>
+
+#include "blockdev-util.h"
+#include "btrfs-util.h"
+#include "fd-util.h"
+#include "fdset.h"
+#include "main-func.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "pretty-print.h"
+#include "process-util.h"
+#include "signal-util.h"
+#include "sort-util.h"
+#include "stat-util.h"
+#include "strv.h"
+#include "time-util.h"
+#include "udevadm.h"
+
+static usec_t arg_timeout_usec = USEC_INFINITY;
+static char **arg_devices = NULL;
+static char **arg_backing = NULL;
+static char **arg_cmdline = NULL;
+static bool arg_print = false;
+
+STATIC_DESTRUCTOR_REGISTER(arg_devices, strv_freep);
+STATIC_DESTRUCTOR_REGISTER(arg_backing, strv_freep);
+STATIC_DESTRUCTOR_REGISTER(arg_cmdline, strv_freep);
+
+static int help(void) {
+        _cleanup_free_ char *link = NULL;
+        int r;
+
+        r = terminal_urlify_man("udevadm", "8", &link);
+        if (r < 0)
+                return log_oom();
+
+        printf("%s [OPTIONS...] COMMAND\n"
+               "%s [OPTIONS...] --print\n"
+               "\n%sLock a block device and run a comand.%s\n\n"
+               "  -h --help            Print this message\n"
+               "  -V --version         Print version of the program\n"
+               "  -d --device=DEVICE   Block device to lock\n"
+               "  -b --backing=FILE    File whose backing block device to lock\n"
+               "  -t --timeout=SECS    Block at most the specified time waiting for lock\n"
+               "  -p --print           Only show which block device the lock would be taken on\n"
+               "\nSee the %s for details.\n",
+               program_invocation_short_name,
+               program_invocation_short_name,
+               ansi_highlight(),
+               ansi_normal(),
+               link);
+
+        return 0;
+}
+
+static int parse_argv(int argc, char *argv[]) {
+
+        static const struct option options[] = {
+                { "help",    no_argument,       NULL, 'h'      },
+                { "version", no_argument,       NULL, 'V'      },
+                { "device",  required_argument, NULL, 'd'      },
+                { "backing", required_argument, NULL, 'b'      },
+                { "timeout", required_argument, NULL, 't'      },
+                { "print",   no_argument,       NULL, 'p'      },
+                {}
+        };
+
+        int c, r;
+
+        assert(argc >= 0);
+        assert(argv);
+
+        while ((c = getopt_long(argc, argv, arg_print ? "hVd:b:t:p" : "+hVd:b:t:p", options, NULL)) >= 0)
+
+                switch (c) {
+
+                case 'h':
+                        return help();
+
+                case 'V':
+                        return print_version();
+
+                case 'd':
+                case 'b': {
+                        _cleanup_free_ char *s = NULL;
+                        char ***l = c == 'd' ? &arg_devices : &arg_backing;
+
+                        r = path_make_absolute_cwd(optarg, &s);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to make path '%s' absolute: %m", optarg);
+
+                        path_simplify(s);
+
+                        if (strv_consume(l, TAKE_PTR(s)) < 0)
+                                return log_oom();
+
+                        strv_uniq(*l);
+                        break;
+                }
+
+                case 't':
+                        r = parse_sec(optarg, &arg_timeout_usec);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to parse --timeout= parameter: %s", optarg);
+                        break;
+
+                case 'p':
+                        arg_print = true;
+                        break;
+
+                case '?':
+                        return -EINVAL;
+
+                default:
+                        assert_not_reached();
+                }
+
+        if (arg_print) {
+                if (optind != argc)
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "No arguments expected");
+        } else {
+                if (optind + 1 > argc)
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Too few arguments, command to execute.");
+
+                arg_cmdline = strv_copy(argv + optind);
+                if (!arg_cmdline)
+                        return log_oom();
+        }
+
+        if (strv_isempty(arg_devices) && strv_isempty(arg_backing))
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "No devices to lock specified, refusing.");
+
+        return 1;
+}
+
+static int find_devno(
+                dev_t **devnos,
+                size_t *n_devnos,
+                const char *device,
+                bool backing) {
+
+        dev_t devt, whole_devt;
+        struct stat st;
+        int r;
+
+        assert(devnos);
+        assert(n_devnos);
+        assert(*devnos || *n_devnos == 0);
+        assert(device);
+
+        if (stat(device, &st) < 0)
+                return log_error_errno(errno, "Failed to stat '%s': %m", device);
+
+        if (S_ISBLK(st.st_mode))
+                devt = st.st_rdev;
+        else if (!backing)
+                return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "Not a block device: %s", device);
+        else if (!S_ISREG(st.st_mode) && !S_ISDIR(st.st_mode))
+                return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "Not a block device, regular file or directory: %s", device);
+        else if (major(st.st_dev) != 0)
+                devt = st.st_dev;
+        else {
+                _cleanup_close_ int regfd = -1;
+                struct stat st2;
+
+                /* If major(st.st_dev) is zero, this might mean we are backed by btrfs, which needs special
+                 * handing, to get the backing device node. */
+
+                regfd = open(device, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
+                if (regfd < 0)
+                        return log_error_errno(errno, "Failed to open '%s': %m", device);
+
+                /* Extra safety: let's check we are still looking at the same file */
+                if (fstat(regfd, &st2) < 0)
+                        return log_error_errno(errno, "Failed to stat '%s': %m", device);
+                if (!stat_inode_same(&st, &st2))
+                        return log_error_errno(SYNTHETIC_ERRNO(ENXIO), "File '%s' was replaced while we were looking at it.", device);
+
+                r = btrfs_get_block_device_fd(regfd, &devt);
+                if (r == -ENOTTY)
+                        return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "Path '%s' not backed by block device.", device);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to acquire btrfs backing device of '%s': %m", device);
+        }
+
+        r = block_get_whole_disk(devt, &whole_devt);
+        if (r < 0)
+                return log_error_errno(r, "Failed to find whole block device for '%s': %m", device);
+
+        if (typesafe_bsearch(&whole_devt, *devnos, *n_devnos, devt_compare_func)) {
+                log_debug("Device %u:%u already listed for locking, ignoring.", major(whole_devt), minor(whole_devt));
+                return 0;
+        }
+
+        if (!GREEDY_REALLOC(*devnos, *n_devnos + 1))
+                return log_oom();
+
+        (*devnos)[(*n_devnos)++] = whole_devt;
+
+        /* Immediately sort again, to ensure the binary search above will work for the next device we add */
+        typesafe_qsort(*devnos, *n_devnos, devt_compare_func);
+        return 1;
+}
+
+static int lock_device(
+                const char *path,
+                dev_t devno,
+                usec_t deadline) {
+
+        _cleanup_close_ int fd = -1;
+        struct stat st;
+        int r;
+
+        fd = open(path, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
+        if (fd < 0)
+                return log_error_errno(errno, "Failed to open '%s': %m", path);
+
+        if (fstat(fd, &st) < 0)
+                return log_error_errno(errno, "Failed to stat '%s': %m", path);
+
+        /* Extra safety: check that the device still refers to what we think it refers to */
+        if (!S_ISBLK(st.st_mode) || st.st_rdev != devno)
+                return log_error_errno(SYNTHETIC_ERRNO(ENXIO), "Path '%s' no longer refers to specified block device %u:%u: %m", path, major(devno), minor(devno));
+
+        if (flock(fd, LOCK_EX|LOCK_NB) < 0) {
+
+                if (errno != EAGAIN)
+                        return log_error_errno(errno, "Failed to lock device '%s': %m", path);
+
+                if (deadline == 0)
+                        return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Device '%s' is currently locked.", path);
+
+                if (deadline == USEC_INFINITY)  {
+
+                        log_info("Device '%s' is currently locked, waiting…", path);
+
+                        if (flock(fd, LOCK_EX) < 0)
+                                return log_error_errno(errno, "Failed to lock device '%s': %m", path);
+
+                } else {
+                        _cleanup_(sigkill_waitp) pid_t flock_pid = 0;
+
+                        /* flock() doesn't support a time-out. Let's fake one then. The traditional way to do
+                         * this is via alarm()/setitimer()/timer_create(), but that's racy, given that the
+                         * SIGALRM might aleady fire between the alarm() and the flock() in which case the
+                         * flock() is never cancelled and we lock up (this is a short time window, but with
+                         * short timeouts on a loaded machine we might run into it, who knows?). Let's
+                         * instead do the lock out-of-process: fork off a child that does the locking, and
+                         * that we'll wait on and kill if it takes too long. */
+
+                        log_info("Device '%s' is currently locked, waiting %s…",
+                                 path, FORMAT_TIMESPAN(usec_sub_unsigned(deadline, now(CLOCK_MONOTONIC)), 0));
+
+                        BLOCK_SIGNALS(SIGCHLD);
+
+                        r = safe_fork("(timed-flock)", FORK_DEATHSIG|FORK_LOG, &flock_pid);
+                        if (r < 0)
+                                return r;
+                        if (r == 0) {
+                                /* Child */
+
+                                if (flock(fd, LOCK_EX) < 0) {
+                                        log_error_errno(errno, "Failed to lock device '%s': %m", path);
+                                        _exit(EXIT_FAILURE);
+                                }
+
+                                _exit(EXIT_SUCCESS);
+                        }
+
+                        for (;;) {
+                                siginfo_t si;
+                                sigset_t ss;
+                                usec_t n;
+
+                                assert(sigemptyset(&ss) >= 0);
+                                assert(sigaddset(&ss, SIGCHLD) >= 0);
+
+                                n = now(CLOCK_MONOTONIC);
+                                if (n >= deadline)
+                                        return log_error_errno(SYNTHETIC_ERRNO(ETIMEDOUT), "Timeout reached.");
+
+                                r = sigtimedwait(&ss, NULL, TIMESPEC_STORE(deadline - n));
+                                if (r < 0) {
+                                        if (errno != EAGAIN)
+                                                return log_error_errno(errno, "Failed to wait for SIGCHLD: %m");
+
+                                        return log_error_errno(SYNTHETIC_ERRNO(ETIMEDOUT), "Timeout reached.");
+                                }
+
+                                assert(r == SIGCHLD);
+
+                                zero(si);
+
+                                if (waitid(P_PID, flock_pid, &si, WEXITED|WNOHANG|WNOWAIT) < 0)
+                                        return log_error_errno(errno, "Failed to wait for child: %m");
+
+                                if (si.si_pid != 0) {
+                                        assert(si.si_pid == flock_pid);
+
+                                        if (si.si_code != CLD_EXITED || si.si_status != EXIT_SUCCESS)
+                                                return log_error_errno(SYNTHETIC_ERRNO(EPROTO), "Unexpected exit status of file lock child.");
+
+                                        break;
+                                }
+
+                                log_debug("Got SIGCHLD for other child, continuing.");
+                        }
+                }
+        }
+
+        log_debug("Successfully locked %s (%u:%u)…", path, major(devno), minor(devno));
+
+        return TAKE_FD(fd);
+}
+
+int lock_main(int argc, char *argv[], void *userdata) {
+        _cleanup_(fdset_freep) FDSet *fds = NULL;
+        _cleanup_free_ dev_t *devnos = NULL;
+        size_t n_devnos = 0;
+        usec_t deadline;
+        pid_t pid;
+        int r;
+
+        r = parse_argv(argc, argv);
+        if (r <= 0)
+                return r;
+
+        STRV_FOREACH(i, arg_devices) {
+                r = find_devno(&devnos, &n_devnos, *i, /* backing= */ false);
+                if (r < 0)
+                        return r;
+        }
+
+        STRV_FOREACH(i, arg_backing) {
+                r = find_devno(&devnos, &n_devnos, *i, /* backing= */ true);
+                if (r < 0)
+                        return r;
+        }
+
+        assert(n_devnos > 0);
+
+        fds = fdset_new();
+        if (!fds)
+                return log_oom();
+
+        if (IN_SET(arg_timeout_usec, 0, USEC_INFINITY))
+                deadline = arg_timeout_usec;
+        else
+                deadline = usec_add(now(CLOCK_MONOTONIC), arg_timeout_usec);
+
+        for (size_t i = 0; i < n_devnos; i++) {
+                _cleanup_free_ char *node = NULL;
+
+                r = device_path_make_canonical(S_IFBLK, devnos[i], &node);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to format block device path: %m");
+
+                if (arg_print)
+                        printf("%s\n", node);
+                else {
+                        _cleanup_close_ int fd = -1;
+
+                        fd = lock_device(node, devnos[i], deadline);
+                        if (fd < 0)
+                                return fd;
+
+                        r = fdset_put(fds, fd);
+                        if (r < 0)
+                                return log_oom();
+
+                        TAKE_FD(fd);
+                }
+        }
+
+        if (arg_print)
+                return EXIT_SUCCESS;
+
+        /* Ignore SIGINT and allow the forked process to receive it */
+        (void) ignore_signals(SIGINT);
+
+        r = safe_fork("(lock)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_CLOSE_ALL_FDS|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
+        if (r < 0)
+                return r;
+        if (r == 0) {
+                /* Child */
+
+                execvp(arg_cmdline[0], arg_cmdline);
+                log_open();
+                log_error_errno(errno, "Failed to execute %s: %m", arg_cmdline[0]);
+                _exit(EXIT_FAILURE);
+        }
+
+        return wait_for_terminate_and_check(arg_cmdline[0], pid, 0);
+}
diff --git a/src/udev/udevadm.c b/src/udev/udevadm.c
index df23a60c1a..cd3786b416 100644
--- a/src/udev/udevadm.c
+++ b/src/udev/udevadm.c
@@ -27,6 +27,7 @@ static int help(void) {
                 { "test",         "Test an event run"                 },
                 { "test-builtin", "Test a built-in command"           },
                 { "wait",         "Wait for device or device symlink" },
+                { "lock",         "Lock a block device"               },
         };
 
         _cleanup_free_ char *link = NULL;
@@ -103,6 +104,7 @@ static int udevadm_main(int argc, char *argv[]) {
                 { "test",         VERB_ANY, VERB_ANY, 0, test_main    },
                 { "test-builtin", VERB_ANY, VERB_ANY, 0, builtin_main },
                 { "wait",         VERB_ANY, VERB_ANY, 0, wait_main    },
+                { "lock",         VERB_ANY, VERB_ANY, 0, lock_main    },
                 { "version",      VERB_ANY, VERB_ANY, 0, version_main },
                 { "help",         VERB_ANY, VERB_ANY, 0, help_main    },
                 {}
diff --git a/src/udev/udevadm.h b/src/udev/udevadm.h
index 808294ec9d..417611affe 100644
--- a/src/udev/udevadm.h
+++ b/src/udev/udevadm.h
@@ -14,6 +14,7 @@ int hwdb_main(int argc, char *argv[], void *userdata);
 int test_main(int argc, char *argv[], void *userdata);
 int builtin_main(int argc, char *argv[], void *userdata);
 int wait_main(int argc, char *argv[], void *userdata);
+int lock_main(int argc, char *argv[], void *userdata);
 
 static inline int print_version(void) {
         /* Dracut relies on the version being a single integer */