introduce report_errno_and_exit() helper (#35028)

This is a follow for https://github.com/systemd/systemd/pull/34853. In
particular, this comment
https://github.com/systemd/systemd/pull/34853#discussion_r1825837705.

9 files changed, 45 insertions, 74 deletions

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 75bc65652e..ee0edfaf94 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -35,6 +35,7 @@
 #include "fileio.h"
 #include "fs-util.h"
 #include "hostname-util.h"
+#include "io-util.h"
 #include "locale-util.h"
 #include "log.h"
 #include "macro.h"
@@ -2238,3 +2239,18 @@ static const char* const sched_policy_table[] = {
 };
 
 DEFINE_STRING_TABLE_LOOKUP_WITH_FALLBACK(sched_policy, int, INT_MAX);
+
+_noreturn_ void report_errno_and_exit(int errno_fd, int error) {
+        int r;
+
+        if (error >= 0)
+                _exit(EXIT_SUCCESS);
+
+        assert(errno_fd >= 0);
+
+        r = loop_write(errno_fd, &error, sizeof(error));
+        if (r < 0)
+                log_debug_errno(r, "Failed to write errno to errno_fd=%d: %m", errno_fd);
+
+        _exit(EXIT_FAILURE);
+}
diff --git a/src/basic/process-util.h b/src/basic/process-util.h
index cb6d47a5bb..0763b64cff 100644
--- a/src/basic/process-util.h
+++ b/src/basic/process-util.h
@@ -273,3 +273,5 @@ int posix_spawn_wrapper(
 int proc_dir_open(DIR **ret);
 int proc_dir_read(DIR *d, pid_t *ret);
 int proc_dir_read_pidref(DIR *d, PidRef *ret);
+
+_noreturn_ void report_errno_and_exit(int errno_fd, int error);
diff --git a/src/core/exec-invoke.c b/src/core/exec-invoke.c
index 120067a774..2f8924cd01 100644
--- a/src/core/exec-invoke.c
+++ b/src/core/exec-invoke.c
@@ -2165,10 +2165,8 @@ static int setup_private_users(PrivateUsers private_users, uid_t ouid, gid_t ogi
                 errno_pipe[0] = safe_close(errno_pipe[0]);
 
                 /* Wait until the parent unshared the user namespace */
-                if (read(unshare_ready_fd, &c, sizeof(c)) < 0) {
-                        r = -errno;
-                        goto child_fail;
-                }
+                if (read(unshare_ready_fd, &c, sizeof(c)) < 0)
+                        report_errno_and_exit(errno_pipe[1], -errno);
 
                 /* Disable the setgroups() system call in the child user namespace, for good. */
                 a = procfs_file_alloca(ppid, "setgroups");
@@ -2176,14 +2174,14 @@ static int setup_private_users(PrivateUsers private_users, uid_t ouid, gid_t ogi
                 if (fd < 0) {
                         if (errno != ENOENT) {
                                 r = log_debug_errno(errno, "Failed to open %s: %m", a);
-                                goto child_fail;
+                                report_errno_and_exit(errno_pipe[1], r);
                         }
 
                         /* If the file is missing the kernel is too old, let's continue anyway. */
                 } else {
                         if (write(fd, "deny\n", 5) < 0) {
                                 r = log_debug_errno(errno, "Failed to write \"deny\" to %s: %m", a);
-                                goto child_fail;
+                                report_errno_and_exit(errno_pipe[1], r);
                         }
 
                         fd = safe_close(fd);
@@ -2194,12 +2192,14 @@ static int setup_private_users(PrivateUsers private_users, uid_t ouid, gid_t ogi
                 fd = open(a, O_WRONLY|O_CLOEXEC);
                 if (fd < 0) {
                         r = log_debug_errno(errno, "Failed to open %s: %m", a);
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe[1], r);
                 }
+
                 if (write(fd, gid_map, strlen(gid_map)) < 0) {
                         r = log_debug_errno(errno, "Failed to write GID map to %s: %m", a);
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe[1], r);
                 }
+
                 fd = safe_close(fd);
 
                 /* The write the UID map */
@@ -2207,18 +2207,15 @@ static int setup_private_users(PrivateUsers private_users, uid_t ouid, gid_t ogi
                 fd = open(a, O_WRONLY|O_CLOEXEC);
                 if (fd < 0) {
                         r = log_debug_errno(errno, "Failed to open %s: %m", a);
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe[1], r);
                 }
+
                 if (write(fd, uid_map, strlen(uid_map)) < 0) {
                         r = log_debug_errno(errno, "Failed to write UID map to %s: %m", a);
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe[1], r);
                 }
 
                 _exit(EXIT_SUCCESS);
-
-        child_fail:
-                (void) write(errno_pipe[1], &r, sizeof(r));
-                _exit(EXIT_FAILURE);
         }
 
         errno_pipe[1] = safe_close(errno_pipe[1]);
diff --git a/src/machine/operation.c b/src/machine/operation.c
index 0b2139acf0..7d7bfa5062 100644
--- a/src/machine/operation.c
+++ b/src/machine/operation.c
@@ -154,18 +154,3 @@ Operation *operation_free(Operation *o) {
 
         return mfree(o);
 }
-
-_noreturn_ void report_errno_and_exit(int errno_fd, int r) {
-        if (r >= 0)
-                _exit(EXIT_SUCCESS);
-
-        assert(errno_fd >= 0);
-
-        ssize_t n = write(errno_fd, &r, sizeof(r));
-        if (n < 0)
-                log_debug_errno(errno, "Failed to write operation's errno: %m");
-        if (n != sizeof(r))
-                log_debug_errno(SYNTHETIC_ERRNO(EIO), "Sent unexpectedly short message");
-
-        _exit(EXIT_FAILURE);
-}
diff --git a/src/machine/operation.h b/src/machine/operation.h
index ee9149854a..75bf918c2b 100644
--- a/src/machine/operation.h
+++ b/src/machine/operation.h
@@ -39,5 +39,3 @@ static inline int operation_new_with_bus_reply(Manager *manager, Machine *machin
 static inline int operation_new_with_varlink_reply(Manager *manager, Machine *machine, pid_t child, sd_varlink *link, int errno_fd, Operation **ret) {
         return operation_new(manager, machine, child, /* message = */ NULL, link, errno_fd, ret);
 }
-
-void report_errno_and_exit(int errno_fd, int r);
diff --git a/src/shared/dissect-image.c b/src/shared/dissect-image.c
index f12a93d0dc..f9418754a8 100644
--- a/src/shared/dissect-image.c
+++ b/src/shared/dissect-image.c
@@ -3522,7 +3522,7 @@ int dissected_image_acquire_metadata(
                         r = detach_mount_namespace_userns(userns_fd);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to detach mount namespace: %m");
-                        goto inner_fail;
+                        report_errno_and_exit(error_pipe[1], r);
                 }
 
                 r = dissected_image_mount(
@@ -3537,7 +3537,7 @@ int dissected_image_acquire_metadata(
                                 DISSECT_IMAGE_USR_NO_ROOT);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to mount dissected image: %m");
-                        goto inner_fail;
+                        report_errno_and_exit(error_pipe[1], r);
                 }
 
                 for (unsigned k = 0; k < _META_MAX; k++) {
@@ -3609,7 +3609,7 @@ int dissected_image_acquire_metadata(
 
                                 r = loop_write(fds[2*k+1], &found, sizeof(found));
                                 if (r < 0)
-                                        goto inner_fail;
+                                        report_errno_and_exit(error_pipe[1], r);
 
                                 goto next;
                         }
@@ -3629,18 +3629,13 @@ int dissected_image_acquire_metadata(
 
                         r = copy_bytes(fd, fds[2*k+1], UINT64_MAX, 0);
                         if (r < 0)
-                                goto inner_fail;
+                                report_errno_and_exit(error_pipe[1], r);
 
                 next:
                         fds[2*k+1] = safe_close(fds[2*k+1]);
                 }
 
                 _exit(EXIT_SUCCESS);
-
-        inner_fail:
-                /* Let parent know the error */
-                (void) write(error_pipe[1], &r, sizeof(r));
-                _exit(EXIT_FAILURE);
         }
 
         error_pipe[1] = safe_close(error_pipe[1]);
diff --git a/src/shared/elf-util.c b/src/shared/elf-util.c
index 69439b61ef..a3ff1fd3fb 100644
--- a/src/shared/elf-util.c
+++ b/src/shared/elf-util.c
@@ -827,12 +827,12 @@ int parse_elf_object(int fd, const char *executable, const char *root, bool fork
                 if (fork_disable_dump) {
                         r = RET_NERRNO(prctl(PR_SET_DUMPABLE, 0));
                         if (r < 0)
-                                goto child_fail;
+                                report_errno_and_exit(error_pipe[1], r);
                 }
 
                 r = parse_elf(fd, executable, root, ret ? &buf : NULL, ret_package_metadata ? &package_metadata : NULL);
                 if (r < 0)
-                        goto child_fail;
+                        report_errno_and_exit(error_pipe[1], r);
 
                 if (buf) {
                         size_t len = strlen(buf);
@@ -853,7 +853,7 @@ int parse_elf_object(int fd, const char *executable, const char *root, bool fork
                         if (r == -EAGAIN)
                                 log_warning("Write failed, backtrace will be truncated.");
                         else if (r < 0)
-                                goto child_fail;
+                                report_errno_and_exit(error_pipe[1], r);
 
                         return_pipe[1] = safe_close(return_pipe[1]);
                 }
@@ -866,10 +866,8 @@ int parse_elf_object(int fd, const char *executable, const char *root, bool fork
                         (void) fcntl(json_pipe[1], F_SETPIPE_SZ, COREDUMP_PIPE_MAX);
 
                         json_out = take_fdopen(&json_pipe[1], "w");
-                        if (!json_out) {
-                                r = -errno;
-                                goto child_fail;
-                        }
+                        if (!json_out)
+                                report_errno_and_exit(error_pipe[1], -errno);
 
                         r = sd_json_variant_dump(package_metadata, SD_JSON_FORMAT_FLUSH, json_out, NULL);
                         if (r < 0)
@@ -877,10 +875,6 @@ int parse_elf_object(int fd, const char *executable, const char *root, bool fork
                 }
 
                 _exit(EXIT_SUCCESS);
-
-        child_fail:
-                (void) write(error_pipe[1], &r, sizeof(r));
-                _exit(EXIT_FAILURE);
         }
 
         error_pipe[1] = safe_close(error_pipe[1]);
diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c
index 8ef952a035..f04235001d 100644
--- a/src/shared/mount-util.c
+++ b/src/shared/mount-util.c
@@ -1011,26 +1011,18 @@ static int mount_in_namespace_legacy(
                 r = path_extract_filename(mount_outside, &mount_outside_fn);
                 if (r < 0) {
                         log_debug_errno(r, "Failed to extract filename from propagation file or directory '%s': %m", mount_outside);
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe_fd[1], r);
                 }
 
                 mount_inside = path_join(incoming_path, mount_outside_fn);
-                if (!mount_inside) {
-                        r = log_oom_debug();
-                        goto child_fail;
-                }
+                if (!mount_inside)
+                        report_errno_and_exit(errno_pipe_fd[1], log_oom_debug());
 
                 r = mount_nofollow_verbose(LOG_DEBUG, mount_inside, dest, NULL, MS_MOVE, NULL);
                 if (r < 0)
-                        goto child_fail;
+                        report_errno_and_exit(errno_pipe_fd[1], r);
 
                 _exit(EXIT_SUCCESS);
-
-        child_fail:
-                (void) write(errno_pipe_fd[1], &r, sizeof(r));
-                errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
-
-                _exit(EXIT_FAILURE);
         }
 
         errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
@@ -1224,14 +1216,8 @@ static int mount_in_namespace(
 
                         r = mount_exchange_graceful(new_mount_fd, dest, /* mount_beneath= */ true);
                 }
-                if (r < 0) {
-                        (void) write(errno_pipe_fd[1], &r, sizeof(r));
-                        errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
 
-                        _exit(EXIT_FAILURE);
-                }
-
-                _exit(EXIT_SUCCESS);
+                report_errno_and_exit(errno_pipe_fd[1], r);
         }
 
         errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
diff --git a/src/shutdown/umount.c b/src/shutdown/umount.c
index ca6d36e054..4bc01c75e0 100644
--- a/src/shutdown/umount.c
+++ b/src/shutdown/umount.c
@@ -274,8 +274,7 @@ static int remount_with_timeout(MountPoint *m, bool last_try) {
                                        "Failed to remount '%s' read-only: %m",
                                        m->path);
 
-                (void) write(pfd[1], &r, sizeof(r)); /* try to send errno up */
-                _exit(r < 0 ? EXIT_FAILURE : EXIT_SUCCESS);
+                report_errno_and_exit(pfd[1], r);
         }
 
         pfd[1] = safe_close(pfd[1]);
@@ -337,8 +336,7 @@ static int umount_with_timeout(MountPoint *m, bool last_try) {
                                 log_umount_blockers(m->path);
                 }
 
-                (void) write(pfd[1], &r, sizeof(r)); /* try to send errno up */
-                _exit(r < 0 ? EXIT_FAILURE : EXIT_SUCCESS);
+                report_errno_and_exit(pfd[1], r);
         }
 
         pfd[1] = safe_close(pfd[1]);