Re: [Qemu-devel] [PATCH 2/3] qtest: make QEMU our direct child process
On Mon, Feb 17, 2014 at 05:44:55PM +0100, Markus Armbruster wrote: Stefan Hajnoczi stefa...@redhat.com writes: qtest_init() cannot use exec*p() to launch QEMU since the exec*p() functions take an argument array while qtest_init() takes char *extra_args. Therefore we execute /bin/sh -c command-line and let the shell parse the argument string. This left /bin/sh as our child process and our child's child was QEMU. We still want QEMU's pid so the -pidfile option was used to let QEMU report its pid. The pidfile needs to be unlinked when the test case exits or fails. In other words, the pidfile creates a new problem for us! Simplify all this using the shell 'exec' command. It allows us to replace the /bin/sh process with QEMU. Then we no longer need to use -pidfile because we already know our fork child's pid. Note: Yes, it seems silly to exec /bin/sh when we could just exec QEMU directly. But remember qtest_init() takes a single char *extra_args command-line fragment instead of a real argv[] array, so we need /bin/sh's argument parsing behavior. Sounds like a design mistake to me. I wouldn't call char *extra_args a mistake because strings are still simpler to manipulate in C than char *argv[] arrays. So we write less code in test cases and libqtest.c at the expense of a roundabout way to spawn the process. Stefan
Re: [Qemu-devel] [PATCH 2/3] qtest: make QEMU our direct child process
Stefan Hajnoczi stefa...@gmail.com writes: On Mon, Feb 17, 2014 at 05:44:55PM +0100, Markus Armbruster wrote: Stefan Hajnoczi stefa...@redhat.com writes: qtest_init() cannot use exec*p() to launch QEMU since the exec*p() functions take an argument array while qtest_init() takes char *extra_args. Therefore we execute /bin/sh -c command-line and let the shell parse the argument string. This left /bin/sh as our child process and our child's child was QEMU. We still want QEMU's pid so the -pidfile option was used to let QEMU report its pid. The pidfile needs to be unlinked when the test case exits or fails. In other words, the pidfile creates a new problem for us! Simplify all this using the shell 'exec' command. It allows us to replace the /bin/sh process with QEMU. Then we no longer need to use -pidfile because we already know our fork child's pid. Note: Yes, it seems silly to exec /bin/sh when we could just exec QEMU directly. But remember qtest_init() takes a single char *extra_args command-line fragment instead of a real argv[] array, so we need /bin/sh's argument parsing behavior. Sounds like a design mistake to me. I wouldn't call char *extra_args a mistake because strings are still simpler to manipulate in C than char *argv[] arrays. So we write less code in test cases and libqtest.c at the expense of a roundabout way to spawn the process. Building command arguments in a string is deceptively simple. The deception collapses once you add funny characters that make the shell do funny and unexpected things. Our extra_args string manipulations are typically of the form format a bunch of options and option arguments into a string. I suspect using a function to collect a bunch of options and option arguments into an array would be about the same amount of code in most cases. Just sayin'; I'm not objecting to your patch.
[Qemu-devel] [PATCH 2/3] qtest: make QEMU our direct child process
qtest_init() cannot use exec*p() to launch QEMU since the exec*p()
functions take an argument array while qtest_init() takes char
*extra_args. Therefore we execute /bin/sh -c command-line and let the
shell parse the argument string.
This left /bin/sh as our child process and our child's child was QEMU.
We still want QEMU's pid so the -pidfile option was used to let QEMU
report its pid.
The pidfile needs to be unlinked when the test case exits or fails. In
other words, the pidfile creates a new problem for us!
Simplify all this using the shell 'exec' command. It allows us to
replace the /bin/sh process with QEMU. Then we no longer need to use
-pidfile because we already know our fork child's pid.
Note: Yes, it seems silly to exec /bin/sh when we could just exec QEMU
directly. But remember qtest_init() takes a single char *extra_args
command-line fragment instead of a real argv[] array, so we need
/bin/sh's argument parsing behavior.
Signed-off-by: Stefan Hajnoczi stefa...@redhat.com
---
tests/libqtest.c | 34 +-
1 file changed, 5 insertions(+), 29 deletions(-)
diff --git a/tests/libqtest.c b/tests/libqtest.c
index 2876ce4..8b2b2d7 100644
--- a/tests/libqtest.c
+++ b/tests/libqtest.c
@@ -43,7 +43,7 @@ struct QTestState
int qmp_fd;
bool irq_level[MAX_IRQ];
GString *rx;
-pid_t qemu_pid; /* QEMU process spawned by our child */
+pid_t qemu_pid; /* our child QEMU process */
};
#define g_assert_no_errno(ret) do { \
@@ -88,32 +88,14 @@ static int socket_accept(int sock)
return ret;
}
-static pid_t read_pid_file(const char *pid_file)
-{
-FILE *f;
-char buffer[1024];
-pid_t pid = -1;
-
-f = fopen(pid_file, r);
-if (f) {
-if (fgets(buffer, sizeof(buffer), f)) {
-pid = atoi(buffer);
-}
-fclose(f);
-}
-return pid;
-}
-
QTestState *qtest_init(const char *extra_args)
{
QTestState *s;
int sock, qmpsock, i;
gchar *socket_path;
gchar *qmp_socket_path;
-gchar *pid_file;
gchar *command;
const char *qemu_binary;
-pid_t pid;
qemu_binary = getenv(QTEST_QEMU_BINARY);
g_assert(qemu_binary != NULL);
@@ -122,22 +104,20 @@ QTestState *qtest_init(const char *extra_args)
socket_path = g_strdup_printf(/tmp/qtest-%d.sock, getpid());
qmp_socket_path = g_strdup_printf(/tmp/qtest-%d.qmp, getpid());
-pid_file = g_strdup_printf(/tmp/qtest-%d.pid, getpid());
sock = init_socket(socket_path);
qmpsock = init_socket(qmp_socket_path);
-pid = fork();
-if (pid == 0) {
-command = g_strdup_printf(%s
+s-qemu_pid = fork();
+if (s-qemu_pid == 0) {
+command = g_strdup_printf(exec %s
-qtest unix:%s,nowait
-qtest-log /dev/null
-qmp unix:%s,nowait
- -pidfile %s
-machine accel=qtest
-display none
%s, qemu_binary, socket_path,
- qmp_socket_path, pid_file,
+ qmp_socket_path,
extra_args ?: );
execlp(/bin/sh, sh, -c, command, NULL);
exit(1);
@@ -159,10 +139,6 @@ QTestState *qtest_init(const char *extra_args)
qtest_qmp_discard_response(s, );
qtest_qmp_discard_response(s, { 'execute': 'qmp_capabilities' });
-s-qemu_pid = read_pid_file(pid_file);
-unlink(pid_file);
-g_free(pid_file);
-
if (getenv(QTEST_STOP)) {
kill(s-qemu_pid, SIGSTOP);
}
--
1.8.5.3
Re: [Qemu-devel] [PATCH 2/3] qtest: make QEMU our direct child process
Stefan Hajnoczi stefa...@redhat.com writes: qtest_init() cannot use exec*p() to launch QEMU since the exec*p() functions take an argument array while qtest_init() takes char *extra_args. Therefore we execute /bin/sh -c command-line and let the shell parse the argument string. This left /bin/sh as our child process and our child's child was QEMU. We still want QEMU's pid so the -pidfile option was used to let QEMU report its pid. The pidfile needs to be unlinked when the test case exits or fails. In other words, the pidfile creates a new problem for us! Simplify all this using the shell 'exec' command. It allows us to replace the /bin/sh process with QEMU. Then we no longer need to use -pidfile because we already know our fork child's pid. Note: Yes, it seems silly to exec /bin/sh when we could just exec QEMU directly. But remember qtest_init() takes a single char *extra_args command-line fragment instead of a real argv[] array, so we need /bin/sh's argument parsing behavior. Sounds like a design mistake to me. Signed-off-by: Stefan Hajnoczi stefa...@redhat.com Patch looks good.
