Re: [PATCH v2 6/7] qga/commands-posix: use ga_run_command helper when suspending via sysfs

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Mar 01, 2024 at 07:28:57PM +0200, Andrey Drobyshev wrote:
> We replace the direct call to open() with a "sh -c 'echo ...'" call, so
> that it becomes an executable command.

Introduced an indirection via the shell is a significant step
backwards IMHO.

> 
> Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
> ---
>  qga/commands-posix.c | 36 ++++--------------------------------
>  1 file changed, 4 insertions(+), 32 deletions(-)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index dd2a7ad2e6..f3f4a05e2d 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -1921,49 +1921,21 @@ static void linux_sys_state_suspend(SuspendMode mode, Error **errp)
>      Error *local_err = NULL;
>      const char *sysfile_strs[3] = {"disk", "mem", NULL};
>      const char *sysfile_str = sysfile_strs[mode];
> -    pid_t pid;
> -    int status;
>  
>      if (!sysfile_str) {
>          error_setg(errp, "unknown guest suspend mode");
>          return;
>      }
>  
> -    pid = fork();
> -    if (!pid) {
> -        /* child */
> -        int fd;
> -
> -        setsid();
> -        reopen_fd_to_null(0);
> -        reopen_fd_to_null(1);
> -        reopen_fd_to_null(2);
> -
> -        fd = open(LINUX_SYS_STATE_FILE, O_WRONLY);
> -        if (fd < 0) {
> -            _exit(EXIT_FAILURE);
> -        }
> -
> -        if (write(fd, sysfile_str, strlen(sysfile_str)) < 0) {
> -            _exit(EXIT_FAILURE);
> -        }
> -
> -        _exit(EXIT_SUCCESS);


This pre-existing code is strange to me.  Why do we need to fork a
new process in order to write to /sys/power/state ?

Looking at the original commit

  commit 11d0f1255bd5651f628280dc96c4ce9d63ae9236
  Author: Luiz Capitulino <lcapitulino@redhat.com>
  Date:   Tue Feb 28 11:03:03 2012 -0300

    qemu-ga: add guest-suspend-disk
    

The code made a little more sense, as after fork() it first
tried to execve  'pm-utils', and then had the sysfs codepath
as a fallback. IOW having the sysfs code after fork() was a
much easier code structure.

This was all changed in

  commit 246d76eba1944d7e59affb288ec27d7fcfb5d256
  Author: Daniel Henrique Barboza <danielhb413@gmail.com>
  Date:   Thu Jun 21 07:21:50 2018 -0300

    qga: guest_suspend: decoupling pm-utils and sys logic


so the pm-utils logic runs in a separate forked child
from the sysfs logic.

AFAICT, that should have made it completely redundant to
fork a process to access /sys/power/state.

Does anyone know of a reason to keep the fork() here ? Of
not we should just be calling 'g_file_set_contents' without
fork

> -    } else if (pid < 0) {
> -        error_setg_errno(errp, errno, "failed to create child process");
> -        return;
> -    }
> +    g_autofree char *echo_cmd = g_strdup_printf(
> +        "echo %s > " LINUX_SYS_STATE_FILE, sysfile_str);
> +    const char *argv[] = {"sh", "-c", echo_cmd, NULL};
>  
> -    ga_wait_child(pid, &status, &local_err);
> +    ga_run_command(argv, NULL, "suspend", &local_err);
>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
>      }
> -
> -    if (WEXITSTATUS(status)) {
> -        error_setg(errp, "child process has failed to suspend");
> -    }
> -
>  }
>  
>  static void guest_suspend(SuspendMode mode, Error **errp)
> -- 
> 2.39.3
> 
> 

With regards,
Daniel
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