Re: [Qemu-devel] [PATCH] log: Redirect stderr to logfile if deamonized

[Paolo Bonzini]

On 18/02/2016 12:38, Dimitris Aragiorgis wrote:
> In case of daemonize, use the logfile passed with the -D option in
> order to redirect stderr to it instead of /dev/null.
> 
> Also remove some unused code in log.h.
> 
> Signed-off-by: Dimitris Aragiorgis <address@hidden>
> ---
>  include/qemu/log.h |    6 ------
>  os-posix.c         |    6 +++++-
>  util/log.c         |   11 +++++++++--
>  3 files changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/include/qemu/log.h b/include/qemu/log.h
> index 30817f7..dda65fd 100644
> --- a/include/qemu/log.h
> +++ b/include/qemu/log.h
> @@ -94,12 +94,6 @@ static inline void qemu_log_close(void)
>      }
>  }
>  
> -/* Set up a new log file */
> -static inline void qemu_log_set_file(FILE *f)
> -{
> -    qemu_logfile = f;
> -}
> -
>  /* define log items */
>  typedef struct QEMULogItem {
>      int mask;
> diff --git a/os-posix.c b/os-posix.c
> index cce62ed..92fa3ba 100644
> --- a/os-posix.c
> +++ b/os-posix.c
> @@ -37,6 +37,7 @@
>  #include "qemu-options.h"
>  #include "qemu/rcu.h"
>  #include "qemu/error-report.h"
> +#include "qemu/log.h"
>  
>  #ifdef CONFIG_LINUX
>  #include <sys/prctl.h>
> @@ -275,7 +276,10 @@ void os_setup_post(void)
>  
>          dup2(fd, 0);
>          dup2(fd, 1);
> -        dup2(fd, 2);
> +        /* In case -D is given do not redirect stderr to /dev/null */
> +        if (!qemu_logfile) {
> +            dup2(fd, 2);
> +        }
>  
>          close(fd);
>  
> diff --git a/util/log.c b/util/log.c
> index 2709e98..a7ddc7e 100644
> --- a/util/log.c
> +++ b/util/log.c
> @@ -56,13 +56,20 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
>  #ifdef CONFIG_TRACE_LOG
>      qemu_loglevel |= LOG_TRACE;
>  #endif
> -    if (qemu_loglevel && !qemu_logfile) {
> +    if ((qemu_loglevel || is_daemonized()) && !qemu_logfile) {
>          if (logfilename) {
>              qemu_logfile = fopen(logfilename, log_append ? "a" : "w");
>              if (!qemu_logfile) {
>                  perror(logfilename);
>                  _exit(1);
>              }
> +            /* In case we are a daemon redirect stderr to logfile */
> +            if (is_daemonized()) {
> +                dup2(fileno(qemu_logfile), STDERR_FILENO);
> +                fclose(qemu_logfile);
> +                /* This will skip closing logfile in qemu_log_close() */
> +                qemu_logfile = stderr;
> +            }
>          } else {
>              /* Default to stderr if no log file specified */
>              qemu_logfile = stderr;
> @@ -82,7 +89,7 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
>              log_append = 1;
>          }
>      }
> -    if (!qemu_loglevel && qemu_logfile) {
> +    if (!qemu_loglevel && !is_daemonized() && qemu_logfile) {
>          qemu_log_close();
>      }

Why is this necessary?  Perhaps qemu_log_close should dup(1,2) if QEMU
is daemonized.  The rest looks great.

Paolo