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authorLennart Poettering <lennart@poettering.net>2016-08-30 23:18:46 +0200
committerLennart Poettering <lennart@poettering.net>2016-10-07 20:14:38 +0200
commit4b58153dd22172d817055d2a09a0cdf3f4bd9db3 (patch)
tree1050683cb79031b8054c99dd1494ddfff0b09b2c /man/sd_id128_get_machine.xml
parente5d855d364a2a474cb42da618d2e4372619ac61d (diff)
core: add "invocation ID" concept to service manager
This adds a new invocation ID concept to the service manager. The invocation ID identifies each runtime cycle of a unit uniquely. A new randomized 128bit ID is generated each time a unit moves from and inactive to an activating or active state. The primary usecase for this concept is to connect the runtime data PID 1 maintains about a service with the offline data the journal stores about it. Previously we'd use the unit name plus start/stop times, which however is highly racy since the journal will generally process log data after the service already ended. The "invocation ID" kinda matches the "boot ID" concept of the Linux kernel, except that it applies to an individual unit instead of the whole system. The invocation ID is passed to the activated processes as environment variable. It is additionally stored as extended attribute on the cgroup of the unit. The latter is used by journald to automatically retrieve it for each log logged message and attach it to the log entry. The environment variable is very easily accessible, even for unprivileged services. OTOH the extended attribute is only accessible to privileged processes (this is because cgroupfs only supports the "trusted." xattr namespace, not "user."). The environment variable may be altered by services, the extended attribute may not be, hence is the better choice for the journal. Note that reading the invocation ID off the extended attribute from journald is racy, similar to the way reading the unit name for a logging process is. This patch adds APIs to read the invocation ID to sd-id128: sd_id128_get_invocation() may be used in a similar fashion to sd_id128_get_boot(). PID1's own logging is updated to always include the invocation ID when it logs information about a unit. A new bus call GetUnitByInvocationID() is added that allows retrieving a bus path to a unit by its invocation ID. The bus path is built using the invocation ID, thus providing a path for referring to a unit that is valid only for the current runtime cycleof it. Outlook for the future: should the kernel eventually allow passing of cgroup information along AF_UNIX/SOCK_DGRAM messages via a unique cgroup id, then we can alter the invocation ID to be generated as hash from that rather than entirely randomly. This way we can derive the invocation race-freely from the messages.
Diffstat (limited to 'man/sd_id128_get_machine.xml')
-rw-r--r--man/sd_id128_get_machine.xml34
1 files changed, 22 insertions, 12 deletions
diff --git a/man/sd_id128_get_machine.xml b/man/sd_id128_get_machine.xml
index 2ad1f8f728..9a86c24aed 100644
--- a/man/sd_id128_get_machine.xml
+++ b/man/sd_id128_get_machine.xml
@@ -45,6 +45,7 @@
<refnamediv>
<refname>sd_id128_get_machine</refname>
<refname>sd_id128_get_boot</refname>
+ <refname>sd_id128_get_invocation</refname>
<refpurpose>Retrieve 128-bit IDs</refpurpose>
</refnamediv>
@@ -62,6 +63,11 @@
<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
</funcprototype>
+ <funcprototype>
+ <funcdef>int <function>sd_id128_get_invocation</function></funcdef>
+ <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
+ </funcprototype>
+
</funcsynopsis>
</refsynopsisdiv>
@@ -83,11 +89,15 @@
for more information. This function also internally caches the
returned ID to make this call a cheap operation.</para>
- <para>Note that <function>sd_id128_get_boot()</function> always
- returns a UUID v4 compatible ID.
- <function>sd_id128_get_machine()</function> will also return a
- UUID v4-compatible ID on new installations but might not on older.
- It is possible to convert the machine ID into a UUID v4-compatible
+ <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed
+ service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment
+ variable that the service manager sets when activating a service, see
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The
+ ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para>
+
+ <para>Note that <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> always
+ return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible
+ ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible
one. For more information, see
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
@@ -107,11 +117,10 @@
<refsect1>
<title>Notes</title>
- <para>The <function>sd_id128_get_machine()</function> and
- <function>sd_id128_get_boot()</function> interfaces are available
- as a shared library, which can be compiled and linked to with the
- <literal>libsystemd</literal> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- file.</para>
+ <para>The <function>sd_id128_get_machine()</function>, <function>sd_id128_get_boot()</function> and
+ <function>sd_id128_get_invocation()</function> interfaces are available as a shared library, which can be compiled
+ and linked to with the <literal>libsystemd</literal> <citerefentry
+ project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
</refsect1>
<refsect1>
@@ -121,8 +130,9 @@
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
</para>
</refsect1>