[Qemu-devel] [PATCH v2] vl.c: move pidfile creation up the line

[Qemu-devel] [PATCH v2] vl.c: move pidfile creation up the line

[Michael Tokarev]

With current code, pid file is open after various
sockets, chardevs, fsdevs and the like.  This causes
interesting effects, for example when monitor is a
unix-socket, and another qemu instance is already
running, new qemu first "damages" the socket and
next complain that it can't acquire the pid file and
exits, making running qemu unreachable.

Move pid file creation earlier, right after the call
to os_daemonize(), where we know our process id (pid).

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
 vl.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

v2: move the pid file creation even earlier, as per
comment by Markus Armbruster

diff --git a/vl.c b/vl.c
index 368510f..ce7e998 100644
--- a/vl.c
+++ b/vl.c
@@ -4058,6 +4058,11 @@ int main(int argc, char **argv, char **envp)
 
     os_daemonize();
 
+    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
+        error_report("could not acquire pid file: %s", strerror(errno));
+        exit(1);
+    }
+
     if (qemu_init_main_loop(&main_loop_err)) {
         error_report_err(main_loop_err);
         exit(1);
@@ -4335,11 +4340,6 @@ int main(int argc, char **argv, char **envp)
     }
 #endif
 
-    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
-        error_report("could not acquire pid file: %s", strerror(errno));
-        exit(1);
-    }
-
     if (qemu_opts_foreach(qemu_find_opts("device"),
                           device_help_func, NULL, NULL)) {
         exit(0);
-- 
2.1.4

Re: [Qemu-devel] [PATCH v2] vl.c: move pidfile creation up the line

[Daniel P. Berrange]

On Wed, Nov 02, 2016 at 05:18:50PM +0300, Michael Tokarev wrote:
> With current code, pid file is open after various
> sockets, chardevs, fsdevs and the like.  This causes
> interesting effects, for example when monitor is a
> unix-socket, and another qemu instance is already
> running, new qemu first "damages" the socket and
> next complain that it can't acquire the pid file and
> exits, making running qemu unreachable.
> 
> Move pid file creation earlier, right after the call
> to os_daemonize(), where we know our process id (pid).
> 
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
>  vl.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>


Regards,
Daniel
-- 
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Re: [Qemu-devel] [PATCH v2] vl.c: move pidfile creation up the line

[Markus Armbruster]

Michael Tokarev <mjt@tls.msk.ru> writes:

> With current code, pid file is open after various
> sockets, chardevs, fsdevs and the like.  This causes
> interesting effects, for example when monitor is a
> unix-socket, and another qemu instance is already
> running, new qemu first "damages" the socket and
> next complain that it can't acquire the pid file and
> exits, making running qemu unreachable.
>
> Move pid file creation earlier, right after the call
> to os_daemonize(), where we know our process id (pid).
>
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
>  vl.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> v2: move the pid file creation even earlier, as per
> comment by Markus Armbruster
>
> diff --git a/vl.c b/vl.c
> index 368510f..ce7e998 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4058,6 +4058,11 @@ int main(int argc, char **argv, char **envp)
>  
>      os_daemonize();
>  
> +    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
> +        error_report("could not acquire pid file: %s", strerror(errno));
> +        exit(1);
> +    }
> +
>      if (qemu_init_main_loop(&main_loop_err)) {
>          error_report_err(main_loop_err);
>          exit(1);
> @@ -4335,11 +4340,6 @@ int main(int argc, char **argv, char **envp)
>      }
>  #endif
>  
> -    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
> -        error_report("could not acquire pid file: %s", strerror(errno));
> -        exit(1);
> -    }
> -
>      if (qemu_opts_foreach(qemu_find_opts("device"),
>                            device_help_func, NULL, NULL)) {
>          exit(0);

Right after os_daemonize() is as early as possible.  There might be
stuff happening before os_daemonize() that shouldn't, but I'm not
demanding you search for it to get this patch in.

The wider problem: we spread around parsing, checking and acting upon
command line options pretty carelessly, even though checking after
daemonize and acting before it is problematic.

Regardless,
Reviewed-by: Markus Armbruster <armbru@redhat.com>

Re: [Qemu-devel] [PATCH v2] vl.c: move pidfile creation up the line

[Paolo Bonzini]

On 02/11/2016 15:18, Michael Tokarev wrote:
> With current code, pid file is open after various
> sockets, chardevs, fsdevs and the like.  This causes
> interesting effects, for example when monitor is a
> unix-socket, and another qemu instance is already
> running, new qemu first "damages" the socket and
> next complain that it can't acquire the pid file and
> exits, making running qemu unreachable.
> 
> Move pid file creation earlier, right after the call
> to os_daemonize(), where we know our process id (pid).
> 
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
>  vl.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> v2: move the pid file creation even earlier, as per
> comment by Markus Armbruster
> 
> diff --git a/vl.c b/vl.c
> index 368510f..ce7e998 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4058,6 +4058,11 @@ int main(int argc, char **argv, char **envp)
>  
>      os_daemonize();
>  
> +    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
> +        error_report("could not acquire pid file: %s", strerror(errno));
> +        exit(1);
> +    }
> +
>      if (qemu_init_main_loop(&main_loop_err)) {
>          error_report_err(main_loop_err);
>          exit(1);
> @@ -4335,11 +4340,6 @@ int main(int argc, char **argv, char **envp)
>      }
>  #endif
>  
> -    if (pid_file && qemu_create_pidfile(pid_file) != 0) {
> -        error_report("could not acquire pid file: %s", strerror(errno));
> -        exit(1);
> -    }
> -
>      if (qemu_opts_foreach(qemu_find_opts("device"),
>                            device_help_func, NULL, NULL)) {
>          exit(0);
> 

Queued, thanks.

Paolo