Re: [Libguestfs] [PATCH nbdkit 2/2] reflection: Add mode for reflecting server time.

Either wallclock time, uptime or time since client connection can be reflected back to the client in a big endian binary structure. $ nbdkit reflection time --run 'nbdsh --connect $uri -c "sys.stdout.buffer.write(h.pread(12,0))" | hexdump -C' 00000000 00 00 00 00 5d 8f 24 c7 00 04 24 01 \ | / / $ date --date="@$(( 0x5d8f24c7 ))" Sat 28 Sep 10:15:51 BST 2019 $ nbdkit reflection uptime --run 'nbdsh --connect $uri -c "sys.stdout.buffer.write(h.pread(12,0))" | hexdump -C' 00000000 00 00 00 00 00 00 00 00 00 00 60 4b | | 0x604b is about 25ms $ nbdkit reflection conntime --run 'nbdsh --connect $uri -c "sys.stdout.buffer.write(h.pread(12,0))" | hexdump -C' 00000000 00 00 00 00 00 00 00 00 00 00 00 e0 | 0xe0 is about 200μs

Suggested by Eric Blake. --- plugins/reflection/Makefile.am | 1 + .../reflection/nbdkit-reflection-plugin.pod | 41 ++++++++- plugins/reflection/reflection.c | 90 ++++++++++++++++++- 3 files changed, 128 insertions(+), 4 deletions(-) diff --git a/plugins/reflection/Makefile.am b/plugins/reflection/Makefile.am index 40aa786..9544d98 100644 --- a/plugins/reflection/Makefile.am +++ b/plugins/reflection/Makefile.am @@ -42,6 +42,7 @@ nbdkit_reflection_plugin_la_SOURCES = \ nbdkit_reflection_plugin_la_CPPFLAGS = \ -I$(top_srcdir)/include \ + -I$(top_srcdir)/common/include \ $(NULL) nbdkit_reflection_plugin_la_CFLAGS = $(WARNINGS_CFLAGS) nbdkit_reflection_plugin_la_LDFLAGS = \ diff --git a/plugins/reflection/nbdkit-reflection-plugin.pod b/plugins/reflection/nbdkit-reflection-plugin.pod index f971cef..09deb26 100644 --- a/plugins/reflection/nbdkit-reflection-plugin.pod +++ b/plugins/reflection/nbdkit-reflection-plugin.pod @@ -4,7 +4,8 @@ nbdkit-reflection-plugin - reflect client info back to the client =head1 SYNOPSIS - nbdkit reflection [mode=]exportname|base64exportname|address + nbdkit reflection [mode=]exportname|base64exportname|address| + time|uptime|conntime =head1 DESCRIPTION @@ -22,6 +23,10 @@ than this. C<mode=address> creates a disk which contains the client's IP address and port number as a string. +C<mode=time>, C<mode=uptime> and C<mode=conntime> report server +wallclock time, nbdkit uptime, or time since the connection was opened +respectively and may be used to measure latency. + The plugin only supports read-only access. To make the disk writable, add L<nbdkit-cow-filter(1)> on top. @@ -103,6 +108,40 @@ name cannot contain ASCII NUL characters. This is the default mode. +=item [B<mode=>]B<time> + +Reflect server wallclock time as seconds and microseconds since the +Epoch (see L<gettimeofday(2)>): + + ┌────────┬────────┬────────────┬──────────────────────┐ + │ offset │ length │ format │ field │ + ╞════════╪════════╪════════════╪══════════════════════╡ + │ 0 │ 8 │ 64 bit int │ seconds │ + │ │ │ big endian │ │ + ├────────┼────────┼────────────┼──────────────────────┤ + │ 8 │ 4 │ 32 bit int │ microseconds │ + │ │ │ big endian │ │ + └────────┴────────┴────────────┴──────────────────────┘ + +To be able to read this atomically you must read the whole 12 bytes in +a single request. + +Note that exposing server time may be insecure. It is safer to use +C<mode=uptime> or C<mode=conntime> instead. + +=item [B<mode=>]B<uptime> + +Reflect nbdkit uptime in seconds and microseconds (ie. both fields are +C<0> immediately after nbdkit starts, although a client would never be +able to observe this). The format is exactly the same as for +C<mode=time> above. + +=item [B<mode=>]B<conntime> + +Reflect time since the NBD client connection was opened in seconds and +milliseconds. The format is exactly the same as for C<mode=time> +above. + C<mode=> is a magic config key and may be omitted in most cases. See L<nbdkit(1)/Magic parameters>. diff --git a/plugins/reflection/reflection.c b/plugins/reflection/reflection.c index 6fd1962..1459503 100644 --- a/plugins/reflection/reflection.c +++ b/plugins/reflection/reflection.c @@ -35,6 +35,7 @@ #include <stdio.h> #include <stdlib.h> #include <string.h> +#include <sys/time.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> @@ -48,14 +49,29 @@ #include <nbdkit-plugin.h> +#include "byte-swapping.h" +#include "tvdiff.h" + /* The mode. */ enum mode { MODE_EXPORTNAME, MODE_BASE64EXPORTNAME, MODE_ADDRESS, + MODE_TIME, + MODE_UPTIME, + MODE_CONNTIME, }; static enum mode mode = MODE_EXPORTNAME; +/* Plugin load time. */ +static struct timeval load_t; + +static void +reflection_load (void) +{ + gettimeofday (&load_t, NULL); +} + static int reflection_config (const char *key, const char *value) { @@ -73,9 +89,14 @@ reflection_config (const char *key, const char *value) return -1; #endif } - else if (strcasecmp (value, "address") == 0) { + else if (strcasecmp (value, "address") == 0) mode = MODE_ADDRESS; - } + else if (strcasecmp (value, "time") == 0) + mode = MODE_TIME; + else if (strcasecmp (value, "uptime") == 0) + mode = MODE_UPTIME; + else if (strcasecmp (value, "conntime") == 0) + mode = MODE_CONNTIME; else { nbdkit_error ("unknown mode: '%s'", value); return -1; @@ -90,7 +111,8 @@ reflection_config (const char *key, const char *value) } #define reflection_config_help \ - "mode=exportname|base64exportname|address Plugin mode (default exportname)." + "mode=exportname|base64exportname|address|time|uptime\n" \ + " Plugin mode (default exportname)." /* Provide a way to detect if the base64 feature is supported. */ static void @@ -105,6 +127,7 @@ reflection_dump_plugin (void) struct handle { void *data; /* Block device data. */ size_t len; /* Length of data in bytes. */ + struct timeval conn_t; /* Time since connection was opened. */ }; static int @@ -279,6 +302,19 @@ reflection_open (int readonly) } return h; + case MODE_TIME: + case MODE_UPTIME: + case MODE_CONNTIME: + gettimeofday (&h->conn_t, NULL); + h->len = 12; + h->data = malloc (h->len); + if (h->data == NULL) { + nbdkit_error ("malloc: %m"); + free (h); + return NULL; + } + return h; + default: abort (); } @@ -320,6 +356,13 @@ reflection_can_multi_conn (void *handle) */ case MODE_ADDRESS: return 0; + /* All time modes will read different values at different times, + * so all of them are unsafe for multi-conn. + */ + case MODE_TIME: + case MODE_UPTIME: + case MODE_CONNTIME: + return 0; /* Keep GCC happy. */ default: @@ -337,6 +380,42 @@ reflection_can_cache (void *handle) return NBDKIT_CACHE_NATIVE; } +static void +update_time (struct handle *h) +{ + struct timeval tv; + int64_t secs; + int32_t usecs; + char *p; + + gettimeofday (&tv, NULL); + + switch (mode) { + case MODE_TIME: + break; + + case MODE_UPTIME: + subtract_timeval (&load_t, &tv, &tv); + break; + + case MODE_CONNTIME: + subtract_timeval (&h->conn_t, &tv, &tv); + break; + + default: + abort (); + } + + /* Pack the result into the output buffer. */ + secs = tv.tv_sec; + usecs = tv.tv_usec; + secs = htobe64 (secs); + usecs = htobe32 (usecs); + p = h->data; + memcpy (&p[0], &secs, 8); + memcpy (&p[8], &usecs, 4); +} + /* Read data. */ static int reflection_pread (void *handle, void *buf, uint32_t count, uint64_t offset, @@ -344,6 +423,10 @@ reflection_pread (void *handle, void *buf, uint32_t count, uint64_t offset, { struct handle *h = handle; + /* For the time modes we update the data on every read. */ + if (mode == MODE_TIME || mode == MODE_UPTIME || mode == MODE_CONNTIME) + update_time (h); + memcpy (buf, h->data + offset, count); return 0; } @@ -351,6 +434,7 @@ reflection_pread (void *handle, void *buf, uint32_t count, uint64_t offset, static struct nbdkit_plugin plugin = { .name = "reflection", .version = PACKAGE_VERSION, + .load = reflection_load, .config = reflection_config, .config_help = reflection_config_help, .dump_plugin = reflection_dump_plugin, -- 2.23.0 _______________________________________________ Libguestfs mailing list Libguestfs(a)redhat.com https://www.redhat.com/mailman/listinfo/libguestfs