hostnamed: minimize caching of /etc/hostname, /etc/os-release and /etc/machine-info

Instead of reading these files at startup and never again, let's read
them when we need them. As an optimization (in particular as some of
these files contain the data for many fields at once) let's cache the
results as long as the stat data (i.e. mtime) remains stable.

Also, while we are at it, if we can't read any of these props, let's not
fail everything, but continue without the data.

1 files changed, 156 insertions, 24 deletions

diff --git a/src/hostname/hostnamed.c b/src/hostname/hostnamed.c
index 405571ca27..7f6607a527 100644
--- a/src/hostname/hostnamed.c
+++ b/src/hostname/hostnamed.c
@@ -28,6 +28,7 @@
 #include "selinux-util.h"
 #include "service-util.h"
 #include "signal-util.h"
+#include "stat-util.h"
 #include "strv.h"
 #include "user-util.h"
 #include "util.h"
@@ -36,49 +37,89 @@
 #define VALID_DEPLOYMENT_CHARS (DIGITS LETTERS "-.:")
 
 enum {
+        /* Read from /etc/hostname */
         PROP_STATIC_HOSTNAME,
+
+        /* Read from /etc/machine-info */
         PROP_PRETTY_HOSTNAME,
         PROP_ICON_NAME,
         PROP_CHASSIS,
         PROP_DEPLOYMENT,
         PROP_LOCATION,
+
+        /* Read from /etc/os-release (or /usr/lib/os-release) */
         PROP_OS_PRETTY_NAME,
         PROP_OS_CPE_NAME,
-        PROP_HOME_URL,
-        _PROP_MAX
+        PROP_OS_HOME_URL,
+        _PROP_MAX,
+        _PROP_INVALID = -1,
 };
 
 typedef struct Context {
         char *data[_PROP_MAX];
+
+        struct stat etc_hostname_stat;
+        struct stat etc_os_release_stat;
+        struct stat etc_machine_info_stat;
+
         Hashmap *polkit_registry;
 } Context;
 
-static void context_reset(Context *c) {
+static void context_reset(Context *c, uint64_t mask) {
         int p;
 
         assert(c);
 
-        for (p = 0; p < _PROP_MAX; p++)
+        for (p = 0; p < _PROP_MAX; p++) {
+                if (!FLAGS_SET(mask, UINT64_C(1) << p))
+                        continue;
+
                 c->data[p] = mfree(c->data[p]);
+        }
 }
 
 static void context_destroy(Context *c) {
         assert(c);
 
-        context_reset(c);
+        context_reset(c, UINT64_MAX);
         bus_verify_polkit_async_registry_free(c->polkit_registry);
 }
 
-static int context_read_data(Context *c) {
+static void context_read_etc_hostname(Context *c) {
+        struct stat current_stat = {};
         int r;
 
         assert(c);
 
-        context_reset(c);
+        if (stat("/etc/hostname", &current_stat) >= 0 &&
+            stat_inode_unmodified(&c->etc_hostname_stat, &current_stat))
+                return;
+
+        context_reset(c, UINT64_C(1) << PROP_STATIC_HOSTNAME);
 
         r = read_etc_hostname(NULL, &c->data[PROP_STATIC_HOSTNAME]);
         if (r < 0 && r != -ENOENT)
-                return r;
+                log_warning_errno(r, "Failed to read /etc/hostname, ignoring: %m");
+
+        c->etc_hostname_stat = current_stat;
+}
+
+static void context_read_machine_info(Context *c) {
+        struct stat current_stat = {};
+        int r;
+
+        assert(c);
+
+        if (stat("/etc/machine-info", &current_stat) >= 0 &&
+            stat_inode_unmodified(&c->etc_machine_info_stat, &current_stat))
+                return;
+
+        context_reset(c,
+                      (UINT64_C(1) << PROP_PRETTY_HOSTNAME) |
+                      (UINT64_C(1) << PROP_ICON_NAME) |
+                      (UINT64_C(1) << PROP_CHASSIS) |
+                      (UINT64_C(1) << PROP_DEPLOYMENT) |
+                      (UINT64_C(1) << PROP_LOCATION));
 
         r = parse_env_file(NULL, "/etc/machine-info",
                            "PRETTY_HOSTNAME", &c->data[PROP_PRETTY_HOSTNAME],
@@ -87,17 +128,36 @@ static int context_read_data(Context *c) {
                            "DEPLOYMENT", &c->data[PROP_DEPLOYMENT],
                            "LOCATION", &c->data[PROP_LOCATION]);
         if (r < 0 && r != -ENOENT)
-                return r;
+                log_warning_errno(r, "Failed to read /etc/machine-info, ignoring: %m");
+
+        c->etc_machine_info_stat = current_stat;
+}
+
+static void context_read_os_release(Context *c) {
+        struct stat current_stat = {};
+        int r;
+
+        assert(c);
+
+        if ((stat("/etc/os-release", &current_stat) >= 0 ||
+             stat("/usr/lib/os-release", &current_stat) >= 0) &&
+            stat_inode_unmodified(&c->etc_os_release_stat, &current_stat))
+                return;
+
+        context_reset(c,
+                      (UINT64_C(1) << PROP_OS_PRETTY_NAME) |
+                      (UINT64_C(1) << PROP_OS_CPE_NAME) |
+                      (UINT64_C(1) << PROP_OS_HOME_URL));
 
         r = parse_os_release(NULL,
                              "PRETTY_NAME", &c->data[PROP_OS_PRETTY_NAME],
                              "CPE_NAME", &c->data[PROP_OS_CPE_NAME],
-                             "HOME_URL", &c->data[PROP_HOME_URL],
+                             "HOME_URL", &c->data[PROP_OS_HOME_URL],
                              NULL);
         if (r < 0 && r != -ENOENT)
-                return r;
+                log_warning_errno(r, "Failed to read os-release file, ignoring: %m");
 
-        return 0;
+        c->etc_os_release_stat = current_stat;
 }
 
 static bool valid_chassis(const char *chassis) {
@@ -283,7 +343,6 @@ static int context_update_kernel_hostname(
 }
 
 static int context_write_data_static_hostname(Context *c) {
-
         assert(c);
 
         if (isempty(c->data[PROP_STATIC_HOSTNAME])) {
@@ -368,6 +427,73 @@ static int property_get_hostname(
         return sd_bus_message_append(reply, "s", current);
 }
 
+static int property_get_static_hostname(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Context *c = userdata;
+        assert(c);
+
+        context_read_etc_hostname(c);
+
+        return sd_bus_message_append(reply, "s", c->data[PROP_STATIC_HOSTNAME]);
+}
+
+static int property_get_machine_info_field(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        sd_bus_slot *slot;
+        Context *c;
+
+        /* Acquire the context object without this property's userdata offset added. Explanation: we want
+         * access to two pointers here: a) the main context object we cache all properties in, and b) the
+         * pointer to the property field inside the context object that we are supposed to update and
+         * use. The latter (b) we get in the 'userdata' function parameter, and sd-bus calculates that for us
+         * from the 'userdata' pointer we supplied when the vtable was registered, with the offset we
+         * specified in the vtable added on top. To get the former (a) we need the 'userdata' pointer from
+         * the vtable registration directly, without the offset added. Hence we ask sd-bus what the slot
+         * object is (which encapsulates the vtable registration), and then query the 'userdata' field
+         * directly off it. */
+        assert_se(slot = sd_bus_get_current_slot(bus));
+        assert_se(c = sd_bus_slot_get_userdata(slot));
+
+        context_read_machine_info(c);
+
+        return sd_bus_message_append(reply, "s", *(char**) userdata);
+}
+
+static int property_get_os_release_field(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        sd_bus_slot *slot;
+        Context *c;
+
+        /* As above, acquire the current context without this property's userdata offset added. */
+        assert_se(slot = sd_bus_get_current_slot(bus));
+        assert_se(c = sd_bus_slot_get_userdata(slot));
+
+        context_read_os_release(c);
+
+        return sd_bus_message_append(reply, "s", *(char**) userdata);
+}
+
 static int property_get_icon_name(
                 sd_bus *bus,
                 const char *path,
@@ -381,6 +507,8 @@ static int property_get_icon_name(
         Context *c = userdata;
         const char *name;
 
+        context_read_machine_info(c);
+
         if (isempty(c->data[PROP_ICON_NAME]))
                 name = n = context_fallback_icon_name(c);
         else
@@ -404,6 +532,8 @@ static int property_get_chassis(
         Context *c = userdata;
         const char *name;
 
+        context_read_machine_info(c);
+
         if (isempty(c->data[PROP_CHASSIS]))
                 name = fallback_chassis();
         else
@@ -441,6 +571,8 @@ static int method_set_hostname(sd_bus_message *m, void *userdata, sd_bus_error *
         if (r < 0)
                 return r;
 
+        context_read_etc_hostname(c);
+
         if (isempty(name))
                 name = c->data[PROP_STATIC_HOSTNAME];
 
@@ -496,6 +628,8 @@ static int method_set_static_hostname(sd_bus_message *m, void *userdata, sd_bus_
 
         name = empty_to_null(name);
 
+        context_read_etc_hostname(c);
+
         if (streq_ptr(name, c->data[PROP_STATIC_HOSTNAME]))
                 return sd_bus_reply_method_return(m, NULL);
 
@@ -553,6 +687,8 @@ static int set_machine_info(Context *c, sd_bus_message *m, int prop, sd_bus_mess
 
         name = empty_to_null(name);
 
+        context_read_machine_info(c);
+
         if (streq_ptr(name, c->data[prop]))
                 return sd_bus_reply_method_return(m, NULL);
 
@@ -695,18 +831,18 @@ static int method_get_product_uuid(sd_bus_message *m, void *userdata, sd_bus_err
 static const sd_bus_vtable hostname_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Hostname", "s", property_get_hostname, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("StaticHostname", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_STATIC_HOSTNAME, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("PrettyHostname", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_PRETTY_HOSTNAME, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("StaticHostname", "s", property_get_static_hostname, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("PrettyHostname", "s", property_get_machine_info_field, offsetof(Context, data) + sizeof(char*) * PROP_PRETTY_HOSTNAME, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("IconName", "s", property_get_icon_name, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("Chassis", "s", property_get_chassis, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("Deployment", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_DEPLOYMENT, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
-        SD_BUS_PROPERTY("Location", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_LOCATION, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("Deployment", "s", property_get_machine_info_field, offsetof(Context, data) + sizeof(char*) * PROP_DEPLOYMENT, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("Location", "s", property_get_machine_info_field, offsetof(Context, data) + sizeof(char*) * PROP_LOCATION, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("KernelName", "s", property_get_uname_field, offsetof(struct utsname, sysname), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("KernelRelease", "s", property_get_uname_field, offsetof(struct utsname, release), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("KernelVersion", "s", property_get_uname_field, offsetof(struct utsname, version), SD_BUS_VTABLE_ABSOLUTE_OFFSET|SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("OperatingSystemPrettyName", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_OS_PRETTY_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("OperatingSystemCPEName", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_OS_CPE_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("HomeURL", "s", NULL, offsetof(Context, data) + sizeof(char*) * PROP_HOME_URL, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("OperatingSystemPrettyName", "s", property_get_os_release_field, offsetof(Context, data) + sizeof(char*) * PROP_OS_PRETTY_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("OperatingSystemCPEName", "s", property_get_os_release_field, offsetof(Context, data) + sizeof(char*) * PROP_OS_CPE_NAME, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("HomeURL", "s", property_get_os_release_field, offsetof(Context, data) + sizeof(char*) * PROP_OS_HOME_URL, SD_BUS_VTABLE_PROPERTY_CONST),
 
         SD_BUS_METHOD_WITH_NAMES("SetHostname",
                                  "sb",
@@ -849,10 +985,6 @@ static int run(int argc, char *argv[]) {
         if (r < 0)
                 return r;
 
-        r = context_read_data(&context);
-        if (r < 0)
-                return log_error_errno(r, "Failed to read hostname and machine information: %m");
-
         r = bus_event_loop_with_idle(event, bus, "org.freedesktop.hostname1", DEFAULT_EXIT_USEC, NULL, NULL);
         if (r < 0)
                 return log_error_errno(r, "Failed to run event loop: %m");