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sd-booted: update sd_booted() check a bit

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Previously we were testing whether /sys/fs/cgroup/systemd/ was a mount
point. This might be problematic however, when the cgroup trees are bind
mounted into a container from the host (which should be absolutely
valid), which might create the impression that the container was running
systemd, but only the host actually is.

Replace this by a check for the existance of the directory
/run/systemd/system/, which should work unconditionally, since /run can
never be a bind mount but *must* be a tmpfs on systemd systems, which is
flushed at boots. This means that data in /run always reflects
information about the current boot, and only of the local container,
which makes it the perfect choice for a check like this.

(As side effect this is nice to Ubuntu people who now use logind with
the systemd cgroup hierarchy, where the old sd_booted() check misdetects
systemd, even though they still run legacy Upstart.)
This commit is contained in:
Lennart Poettering 2013-03-15 16:41:40 +01:00
parent 961e452692
commit 66e411811b
3 changed files with 15 additions and 15 deletions
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9
man/sd_booted.xml
View file

@ -85,11 +85,10 @@
implementation.</para>
<para>Internally, this function checks whether the
<filename>/sys/fs/cgroup/systemd</filename> virtual file
system is mounted, by comparing the st_dev value of
the <function>stat()</function> data of
<filename>/sys/fs/cgroup</filename> and
<filename>/sys/fs/cgroup/systemd</filename>.</para>
directory <filename>/run/systemd/system/</filename>
exists. A simple check like this can also be
implemented trivially in shell or any other
language.</para>
<para>For details about the algorithm check the
liberally licensed reference implementation sources:

6
src/core/mount-setup.c
View file

@ -440,7 +440,11 @@ int mount_setup(bool loaded_policy) {
if (mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL) < 0)
log_warning("Failed to set up the root directory for shared mount propagation: %m");
/* Create a few directories we always want around */
/* Create a few directories we always want around, Note that
* sd_booted() checks for /run/systemd/system, so this mkdir
* really needs to stay for good, otherwise software that
* copied sd-daemon.c into their sources will misdetect
* systemd. */
mkdir_label("/run/systemd", 0755);
mkdir_label("/run/systemd/system", 0755);

15
src/libsystemd-daemon/sd-daemon.c
View file

@ -519,18 +519,15 @@ _sd_export_ int sd_booted(void) {
#if defined(DISABLE_SYSTEMD) || !defined(__linux__)
return 0;
#else
struct stat st;
struct stat a, b;
/* We test whether the runtime unit file directory has been
* created. This takes place in mount-setup.c, so is
* guaranteed to happen very early during boot. */
/* We simply test whether the systemd cgroup hierarchy is
* mounted */
if (lstat("/sys/fs/cgroup", &a) < 0)
if (lstat("/run/systemd/system/", &st) < 0)
return 0;
if (lstat("/sys/fs/cgroup/systemd", &b) < 0)
return 0;
return a.st_dev != b.st_dev;
return !!S_ISDIR(st.st_mode);
#endif
}