core/exec: add a named-descriptor option ("fd") for streams (#4179)

This commit adds a `fd` option to `StandardInput=`,
`StandardOutput=` and `StandardError=` properties in order to
connect standard streams to externally named descriptors provided
by some socket units.

This option looks for a file descriptor named as the corresponding
stream. Custom names can be specified, separated by a colon.
If multiple name-matches exist, the first matching fd will be used.

1 files changed, 85 insertions, 1 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index b8720d7d3d..1a7f770db1 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -627,6 +627,53 @@ static int property_get_syslog_facility(
         return sd_bus_message_append(reply, "i", LOG_FAC(c->syslog_priority));
 }
 
+static int property_get_input_fdname(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        ExecContext *c = userdata;
+        const char *name;
+
+        assert(bus);
+        assert(c);
+        assert(property);
+        assert(reply);
+
+        name = exec_context_fdname(c, STDIN_FILENO);
+
+        return sd_bus_message_append(reply, "s", name);
+}
+
+static int property_get_output_fdname(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        ExecContext *c = userdata;
+        const char *name = NULL;
+
+        assert(bus);
+        assert(c);
+        assert(property);
+        assert(reply);
+
+        if (c->std_output == EXEC_OUTPUT_NAMED_FD && streq(property, "StandardOutputFileDescriptorName"))
+                name = exec_context_fdname(c, STDOUT_FILENO);
+        else if (c->std_error == EXEC_OUTPUT_NAMED_FD && streq(property, "StandardErrorFileDescriptorName"))
+                name = exec_context_fdname(c, STDERR_FILENO);
+
+        return sd_bus_message_append(reply, "s", name);
+}
+
 const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Environment", "as", NULL, offsetof(ExecContext, environment), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -677,8 +724,11 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("CPUSchedulingResetOnFork", "b", bus_property_get_bool, offsetof(ExecContext, cpu_sched_reset_on_fork), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("NonBlocking", "b", bus_property_get_bool, offsetof(ExecContext, non_blocking), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StandardInput", "s", property_get_exec_input, offsetof(ExecContext, std_input), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("StandardInputFileDescriptorName", "s", property_get_input_fdname, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StandardOutput", "s", bus_property_get_exec_output, offsetof(ExecContext, std_output), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("StandardOutputFileDescriptorName", "s", property_get_output_fdname, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StandardError", "s", bus_property_get_exec_output, offsetof(ExecContext, std_error), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("StandardErrorFileDescriptorName", "s", property_get_output_fdname, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TTYPath", "s", NULL, offsetof(ExecContext, tty_path), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TTYReset", "b", bus_property_get_bool, offsetof(ExecContext, tty_reset), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TTYVHangup", "b", bus_property_get_bool, offsetof(ExecContext, tty_vhangup), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -1030,7 +1080,6 @@ int bus_exec_context_set_transient_property(
 
                 return 1;
 
-
         } else if (streq(name, "StandardOutput")) {
                 const char *s;
                 ExecOutput p;
@@ -1072,6 +1121,41 @@ int bus_exec_context_set_transient_property(
                 return 1;
 
         } else if (STR_IN_SET(name,
+                              "StandardInputFileDescriptorName", "StandardOutputFileDescriptorName", "StandardErrorFileDescriptorName")) {
+                const char *s;
+
+                r = sd_bus_message_read(message, "s", &s);
+                if (r < 0)
+                        return r;
+
+                if (!fdname_is_valid(s))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid file descriptor name");
+
+                if (mode != UNIT_CHECK) {
+                        if (streq(name, "StandardInputFileDescriptorName")) {
+                                c->std_input = EXEC_INPUT_NAMED_FD;
+                                r = free_and_strdup(&c->stdio_fdname[STDIN_FILENO], s);
+                                if (r < 0)
+                                        return r;
+                                unit_write_drop_in_private_format(u, mode, name, "StandardInput=fd:%s", s);
+                        } else if (streq(name, "StandardOutputFileDescriptorName")) {
+                                c->std_output = EXEC_OUTPUT_NAMED_FD;
+                                r = free_and_strdup(&c->stdio_fdname[STDOUT_FILENO], s);
+                                if (r < 0)
+                                        return r;
+                                unit_write_drop_in_private_format(u, mode, name, "StandardOutput=fd:%s", s);
+                        } else if (streq(name, "StandardErrorFileDescriptorName")) {
+                                c->std_error = EXEC_OUTPUT_NAMED_FD;
+                                r = free_and_strdup(&c->stdio_fdname[STDERR_FILENO], s);
+                                if (r < 0)
+                                        return r;
+                                unit_write_drop_in_private_format(u, mode, name, "StandardError=fd:%s", s);
+                        }
+                }
+
+                return 1;
+
+        } else if (STR_IN_SET(name,
                               "IgnoreSIGPIPE", "TTYVHangup", "TTYReset",
                               "PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers",
                               "NoNewPrivileges", "SyslogLevelPrefix", "MemoryDenyWriteExecute",