tst: Extend cross-test-ssh.sh to specify if target date can be altered

This code adds new flag - '--allow-time-setting' to cross-test-ssh.sh
script to indicate if it is allowed to alter the date on the system
on which tests are executed. This change is supposed to be used with
test systems, which use virtual machines for testing.

The GLIBC_TEST_ALLOW_TIME_SETTING env variable is exported to the
remote environment on which the eligible test is run and brings no
functional change when it is not.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

INSTALL

@@ -347,6 +347,21 @@ is the absolute directory name for the main source directory and
 HOSTNAME is the host name of a system that can run the newly built
 binaries of the GNU C Library.  The source and build directories must be
 visible at the same locations on both the build system and HOSTNAME.
+The 'cross-test-ssh.sh' script requires 'flock' from 'util-linux' to
+work when GLIBC_TEST_ALLOW_TIME_SETTING environment variable is set.
+
+   It is also possible to execute tests, which require setting the date
+on the target machine.  Following use cases are supported:
+   * 'GLIBC_TEST_ALLOW_TIME_SETTING' is set in the environment in which
+     eligible tests are executed and have the privilege to run
+     'clock_settime'.  In this case, nothing prevents those tests from
+     running in parallel, so the caller shall assure that those tests
+     are serialized or provide a proper wrapper script for them.
+
+   * The 'cross-test-ssh.sh' script is used and one passes the
+     '--allow-time-setting' flag.  In this case, both sets
+     'GLIBC_TEST_ALLOW_TIME_SETTING' and serialization of test execution
+     are assured automatically.
 
    In general, when testing the GNU C Library, 'test-wrapper' may be set
 to the name and arguments of any program to run newly built binaries.

manual/install.texi

@@ -379,6 +379,26 @@ directory and @var{hostname} is the host name of a system that can run
 the newly built binaries of @theglibc{}.  The source and build
 directories must be visible at the same locations on both the build
 system and @var{hostname}.
+The @samp{cross-test-ssh.sh} script requires @samp{flock} from
+@samp{util-linux} to work when @var{glibc_test_allow_time_setting}
+environment variable is set.
+
+It is also possible to execute tests, which require setting the date on
+the target machine.  Following use cases are supported:
+@itemize @bullet
+@item
+@code{GLIBC_TEST_ALLOW_TIME_SETTING} is set in the environment in
+which eligible tests are executed and have the privilege to run
+@code{clock_settime}.  In this case, nothing prevents those tests from
+running in parallel, so the caller shall assure that those tests
+are serialized or provide a proper wrapper script for them.
+
+@item
+The @code{cross-test-ssh.sh} script is used and one passes the
+@option{--allow-time-setting} flag.  In this case, both sets
+@code{GLIBC_TEST_ALLOW_TIME_SETTING} and serialization of test
+execution are assured automatically.
+@end itemize
 
 In general, when testing @theglibc{}, @samp{test-wrapper} may be set
 to the name and arguments of any program to run newly built binaries.

scripts/cross-test-ssh.sh

@@ -22,7 +22,7 @@
 
 progname="$(basename $0)"
 
-usage="usage: ${progname} [--ssh SSH] HOST COMMAND ..."
+usage="usage: ${progname} [--ssh SSH] [--allow-time-setting] HOST COMMAND ..."
 help="Run a glibc test COMMAND on the remote machine HOST, via ssh,
 preserving the current working directory, and respecting quoting.
 
@@ -32,6 +32,10 @@ instead of ordinary 'ssh'.
 If the '--timeoutfactor FACTOR' flag is present, set TIMEOUTFACTOR on
 the remote machine to the specified FACTOR.
 
+If the '--allow-time-setting' flag is present, set
+GLIBC_TEST_ALLOW_TIME_SETTING on the remote machine to indicate that
+time can be safely adjusted (e.g. on a virtual machine).
+
 To use this to run glibc tests, invoke the tests as follows:
 
   $ make test-wrapper='ABSPATH/cross-test-ssh.sh HOST' tests
@@ -81,6 +85,10 @@ while [ $# -gt 0 ]; do
       timeoutfactor="$1"
       ;;
 
+    "--allow-time-setting")
+      settimeallowed="1"
+      ;;
+
     "--help")
       echo "$usage"
       echo "$help"
@@ -127,6 +135,21 @@ if [ "$timeoutfactor" ]; then
 ${command}"
 fi
 
+# Add command to set the info that time on target can be adjusted,
+# if required.
+# Serialize execution of this script on target to prevent from unintended
+# change of target time.
+FLOCK_PATH="${FLOCK_PATH:-/var/lock/clock_settime}"
+FLOCK_TIMEOUT="${FLOCK_TIMEOUT:-20}"
+FLOCK_FD="${FLOCK_FD:-99}"
+if [ "$settimeallowed" ]; then
+  command="exec ${FLOCK_FD}<>${FLOCK_PATH}
+flock -w ${FLOCK_TIMEOUT} ${FLOCK_FD}
+if [ $? -ne 0 ]; then exit 1; fi
+export GLIBC_TEST_ALLOW_TIME_SETTING=1
+${command}"
+fi
+
 # HOST's sshd simply concatenates its arguments with spaces and
 # passes them to some shell.  We want to force the use of /bin/sh,
 # so we need to re-quote the whole command to ensure it appears as