Support passing arguments to the reboot syscall

This is required for the Raspberry Pi's tryboot feature.

README.md

@@ -411,6 +411,20 @@ partition on Nerves. SeedRNG is called right before a `--pre-run-exec` and at
 shutdown after all other processes have exited. Errors are ignored, but logged
 as warnings. Specify `-v` to `erlinit` to see some information messages.
 
+## Passing arguments to reboot
+
+It's possible to pass arguments to the `reboot(2)` syscall. This feature is used
+by the Raspberry Pi bootloader to support its automatic failback mechanism. See
+the [tryboot
+documentation](https://www.raspberrypi.com/documentation/computers/config_txt.html#the-tryboot-filter)
+for high level details for Raspberry Pi OS. The main difference with `erlinit` is
+how the `"0 tryboot"` parameter gets passed to the kernel. Raspberry Pi OS uses
+Systemd and Systemd's `reboot` implementation writes the parameter to
+`/run/systemd/reboot-param` to pass it to PID 1. With `erlinit`, you're
+responsible for writing `"0 tryboot"` to `/run/reboot-param` and then running
+`reboot`. `erlinit` will see file and pass the argument to the kernel as
+intended.
+
 ## Hacking
 
 It seems like there are an endless number of small tweaks to `erlinit` that

src/compat/compat.c

@@ -2,6 +2,10 @@
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
+#include <err.h>
+
+#include "sys/syscall.h"
+#include "linux/reboot.h"
 
 static int sigtimedwait_signal = 0;
 static int sigtimedwait_counter = 0;
@@ -72,4 +76,21 @@ ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
     (void) flags;
     memset(buf, 0xaa, buflen);
     return buflen;
-}
+}
+
+// This is only needed for reboot, so hardcode most argument checks.
+long fake_syscall(long number, unsigned int magic, unsigned int magic2, unsigned int cmd, const void *arg)
+{
+    if (number != SYS_reboot)
+        errx(1, "Only syscall expecting to receive is the reboot one?");
+
+    if (magic != LINUX_REBOOT_MAGIC1 || (magic2 != LINUX_REBOOT_MAGIC1 && magic2 != LINUX_REBOOT_MAGIC2))
+        errx(1, "Unexpected magic passed to reboot syscall");
+
+    if (cmd != LINUX_REBOOT_CMD_RESTART2)
+        errx(1, "Expected LINUX_REBOOT_CMD_RESTART2 to be passed to reboot with arguments");
+
+    // On Linux, the fixture logs this, but that doesn't work on MacOS, so fake it.
+    fprintf(stderr, "fixture: reboot(0x%08x, \"%s\")", cmd, (const char *) arg);
+    return 0;
+}

src/compat/compat.h

@@ -71,4 +71,8 @@ int sigprocmask_noop(int how, const sigset_t *restrict set, sigset_t *restrict o
 #define RLIMIT_RTTIME     104
 #define RLIMIT_MSGQUEUE   105
 
+// syscall
+#define syscall fake_syscall
+long fake_syscall(long number, unsigned int magic, unsigned int magic2, unsigned int cmd, const void *arg);
+
 #endif

src/compat/sys/syscall.h

@@ -0,0 +1,6 @@
+#ifndef _SYS_SYSCALL_H
+#define _SYS_SYSCALL_H
+
+#define SYS_reboot 142
+
+#endif

src/erlinit.c

@@ -903,6 +903,22 @@ static void wait_for_graceful_shutdown(pid_t pid, struct erlinit_exit_info *exit
     clock_gettime(CLOCK_MONOTONIC, &exit_info->shutdown_complete);
 }
 
+static void read_reboot_args(char *args, size_t max_length)
+{
+    FILE *fp = fopen("/run/reboot-param", "r");
+    if (fp == NULL) {
+        args[0] = '\0';
+        return;
+    }
+
+    if (fgets(args, max_length, fp) != NULL) {
+        trim_whitespace(args);
+    } else {
+        args[0] = '\0';
+    }
+    fclose(fp);
+}
+
 static void fork_and_wait(struct erlinit_exit_info *exit_info)
 {
     sigset_t mask;
@@ -962,7 +978,8 @@ static void fork_and_wait(struct erlinit_exit_info *exit_info)
         } else if (rc == SIGTERM) {
             // Reboot request
             debug("sigterm -> reboot");
-            exit_info->desired_reboot_cmd = LINUX_REBOOT_CMD_RESTART;
+            read_reboot_args(exit_info->reboot_args, sizeof(exit_info->reboot_args));
+            exit_info->desired_reboot_cmd = exit_info->reboot_args[0] == '\0' ? LINUX_REBOOT_CMD_RESTART : LINUX_REBOOT_CMD_RESTART2;
             wait_for_graceful_shutdown(pid, exit_info);
             break;
         } else if (rc == SIGUSR2) {
@@ -994,6 +1011,13 @@ static void fork_and_wait(struct erlinit_exit_info *exit_info)
     }
 }
 
+
+/* See reboot(2) for details about the reboot command with arguments (arg is a NULL-terminated string)*/
+#include <sys/syscall.h>
+static inline int reboot_with_args(int cmd, const void *arg) {
+    return (int) syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd, arg);
+}
+
 int main(int argc, char *argv[])
 {
     if (getpid() != 1)
@@ -1078,7 +1102,10 @@ int main(int argc, char *argv[])
     close(STDERR_FILENO);
 
     // Reboot/poweroff/halt
-    reboot(exit_info.desired_reboot_cmd);
+    if (exit_info.reboot_args[0] != '\0')
+        reboot_with_args(exit_info.desired_reboot_cmd, exit_info.reboot_args);
+    else
+        reboot(exit_info.desired_reboot_cmd);
 
     // If we get here, oops the kernel.
     return 0;

src/erlinit.h

@@ -95,6 +95,7 @@ struct erlinit_exit_info {
     struct timespec shutdown_start;
     struct timespec shutdown_complete;
     int graceful_shutdown_ok;
+    char reboot_args[32];
 };
 
 // Logging functions
@@ -138,6 +139,9 @@ void shutdown_report_create(const char *path, const struct erlinit_exit_info *in
 // seedrng
 int seedrng(void);
 
+// Utility functions
+void trim_whitespace(char *s);
+
 #ifdef __APPLE__
 #include "compat.h"
 #endif

src/hostname.c

@@ -30,21 +30,6 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <string.h>
 #include <unistd.h>
 
-static void trim_whitespace(char *s)
-{
-    char *left = s;
-    while (*left != 0 && isspace(*left))
-        left++;
-    char *right = s + strlen(s) - 1;
-    while (right >= left && isspace(*right))
-        right--;
-
-    int len = right - left + 1;
-    if (len)
-        memmove(s, left, len);
-    s[len] = 0;
-}
-
 static void kill_whitespace(char *s)
 {
     // This function trims whitespace off the front and back, and if

src/shutdown_report.c

@@ -103,6 +103,8 @@ static void report_exit_info(FILE *fp, const struct erlinit_exit_info *exit_info
     if (WIFSIGNALED(exit_info->wait_status))
         fprintf(fp, "Erlang exited due to signal: %d\n", WTERMSIG(exit_info->wait_status));
     fprintf(fp, "Shutdown action: %s\n", reboot_cmd(exit_info->desired_reboot_cmd));
+    if (exit_info->reboot_args[0] != '\0')
+        fprintf(fp, "Reboot args: %s\n", (const char *) exit_info->reboot_args);
 }
 
 static void report_dmesg(FILE *fp)

src/utility.c

@@ -0,0 +1,42 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2013-16 Frank Hunleth
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+#include "erlinit.h"
+
+#include <ctype.h>
+#include <string.h>
+
+void trim_whitespace(char *s)
+{
+    char *left = s;
+    while (*left != 0 && isspace(*left))
+        left++;
+    char *right = s + strlen(s) - 1;
+    while (right >= left && isspace(*right))
+        right--;
+
+    int len = right - left + 1;
+    if (len)
+        memmove(s, left, len);
+    s[len] = 0;
+}

tests/001_cmdline_verbose

@@ -74,5 +74,6 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF
 

tests/002_config_verbose

@@ -74,4 +74,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/003_run_release

@@ -93,4 +93,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/004_run_deep_release

@@ -94,4 +94,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/005_run_strace

@@ -88,4 +88,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/006_env

@@ -78,4 +78,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/007_multi_release_paths

@@ -96,4 +96,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/008_cmdline_verbose2

@@ -74,4 +74,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/009_mount

@@ -79,4 +79,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/010_uniqueid

@@ -93,4 +93,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/011_etc_hostname

@@ -79,4 +79,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/012_bad_option

@@ -76,4 +76,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/013_bad_option2

@@ -76,4 +76,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/014_tty_warning

@@ -90,4 +90,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/015_multi_mount

@@ -83,4 +83,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/016_erlexec_boot_arg

@@ -79,4 +79,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/017_erlexec_boot_arg_file

@@ -76,4 +76,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/018_run_on_exit

@@ -104,4 +104,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/019_uid_and_gid

@@ -83,4 +83,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/020_pre_run_exec

@@ -104,4 +104,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/021_multi_boot_script

@@ -97,4 +97,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/022_pick_boot_script

@@ -100,4 +100,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/023_pick_boot_script2

@@ -100,4 +100,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/024_pick_missing_boot_script

@@ -101,4 +101,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/025_start_erl_data

@@ -105,4 +105,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/026_bad_start_erl_data

@@ -108,4 +108,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/027_bad_start_erl_data2

@@ -107,4 +107,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/028_boot_script_preference

@@ -97,4 +97,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF

tests/029_funny_named_boot_script

@@ -98,4 +98,5 @@ erlinit: unmounting proc at /proc...
 fixture: umount("/proc")
 erlinit: unmounting sysfs at /sys...
 fixture: umount("/sys")
+fixture: reboot(0x01234567)
 EOF