Re: [RFC v4 PATCH 14/49] mutli-process: build remote command line args

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, Oct 24, 2019 at 05:08:55AM -0400, Jagannathan Raman wrote:
> From: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> ---
>  New patch in v3
> 
>  hw/proxy/qemu-proxy.c         | 80 +++++++++++++++++++++++++++++++++----------
>  include/hw/proxy/qemu-proxy.h |  2 +-
>  2 files changed, 62 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/proxy/qemu-proxy.c b/hw/proxy/qemu-proxy.c
> index baba4da..ca7dd1a 100644
> --- a/hw/proxy/qemu-proxy.c
> +++ b/hw/proxy/qemu-proxy.c
> @@ -45,47 +45,89 @@
>  
>  static void pci_proxy_dev_realize(PCIDevice *dev, Error **errp);
>  
> +static int add_argv(char *command_str, char **argv, int argc)
> +{
> +    int max_args = 64;
> +
> +    if (argc < max_args - 1) {
> +        argv[argc++] = command_str;
> +        argv[argc] = 0;
> +    } else {
> +        return 0;
> +    }
> +
> +    return argc;
> +}
> +
> +static int make_argv(char *command_str, char **argv, int argc)
> +{
> +    int max_args = 64;
> +
> +    char *p2 = strtok(command_str, " ");
> +    while (p2 && argc < max_args - 1) {
> +        argv[argc++] = p2;
> +        p2 = strtok(0, " ");
> +    }
> +    argv[argc] = 0;
> +
> +    return argc;
> +}

So "command" isn't really the command-line, it's a string of options to
append to the hardcoded qemu-scsi-dev command?

This needs to command-line string construction needs to be cleaned up
and the hardcoded qemu-scsi-dev needs to be replaced with an argument.

> +
>  int remote_spawn(PCIProxyDev *pdev, const char *command, Error **errp)

Error handling code is currently inconsistent because there is an int
-errno return value and an errp argument.  For example, errp isn't set
when pdev->managed == true.

The int -errno return value isn't needed.  It can be just be bool and
errp should be set in every single error code path.

>  {
> -    char *args[3];
>      pid_t rpid;
>      int fd[2] = {-1, -1};
>      Error *local_error = NULL;
> +    char *argv[64];
> +    int argc = 0, _argc;
> +    char *sfd;
> +    char *exec_dir;
> +    int rc = -EINVAL;
>  
>      if (pdev->managed) {
>          /* Child is forked by external program (such as libvirt). */
> -        return -1;
> +        return rc;
>      }
>  
>      if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd)) {
>          error_setg(errp, "Unable to create unix socket.");
> -        return -1;
> +        return rc;
>      }
> +    exec_dir = g_strdup_printf("%s/%s", qemu_get_exec_dir(), "qemu-scsi-dev");
> +    argc = add_argv(exec_dir, argv, argc);
> +    sfd = g_strdup_printf("%d", fd[1]);
> +    argc = add_argv(sfd, argv, argc);
> +    _argc = argc;
> +    argc = make_argv((char *)command, argv, argc);
> +
>      /* TODO: Restrict the forked process' permissions and capabilities. */
>      rpid = qemu_fork(&local_error);
>  
>      if (rpid == -1) {
>          error_setg(errp, "Unable to spawn emulation program.");
>          close(fd[0]);
> -        close(fd[1]);
> -        return -1;
> +        goto fail;
>      }
>  
>      if (rpid == 0) {
>          close(fd[0]);
> -
> -        args[0] = g_strdup(command);
> -        args[1] = g_strdup_printf("%d", fd[1]);
> -        args[2] = NULL;
> -        execvp(args[0], (char *const *)args);
> +        execvp(argv[0], (char *const *)argv);
>          exit(1);
>      }
>      pdev->remote_pid = rpid;
> -    pdev->rsocket = fd[0];
> +    pdev->rsocket = fd[1];
> +    pdev->socket = fd[0];

Please choose meaningful names for these fields.  I'm not sure why both
need to be kept around though...

>  
> +    rc = 0;
> +
> +fail:
>      close(fd[1]);
>  
> -    return 0;
> +    for (int i = 0; i < _argc; i++) {
> +        g_free(argv[i]);
> +    }
> +
> +    return rc;
>  }
>  
>  static int get_proxy_sock(PCIDevice *dev)
> @@ -94,7 +136,7 @@ static int get_proxy_sock(PCIDevice *dev)
>  
>      pdev = PCI_PROXY_DEV(dev);
>  
> -    return pdev->rsocket;
> +    return pdev->socket;
>  }
>  
>  static void set_proxy_sock(PCIDevice *dev, int socket)
> @@ -103,7 +145,7 @@ static void set_proxy_sock(PCIDevice *dev, int socket)
>  
>      pdev = PCI_PROXY_DEV(dev);
>  
> -    pdev->rsocket = socket;
> +    pdev->socket = socket;
>      pdev->managed = true;
>  
>  }
> @@ -198,16 +240,16 @@ static void pci_proxy_dev_register_types(void)
>  
>  type_init(pci_proxy_dev_register_types)
>  
> -static void init_proxy(PCIDevice *dev, char *command, Error **errp)
> +static void init_proxy(PCIDevice *dev, char *command, bool need_spawn, Error **errp)
>  {
>      PCIProxyDev *pdev = PCI_PROXY_DEV(dev);
>      Error *local_error = NULL;
>  
>      if (!pdev->managed) {
> -        if (command) {
> -            remote_spawn(pdev, command, &local_error);
> -        } else {
> -            return;
> +        if (need_spawn) {

pdev->managed, command == NULL, need_spawn are all ways of checking
whether the remote process needs to be spawned.  Why are all of them
necessary and can they be simplified?

> +            if (!remote_spawn(pdev, command, &local_error)) {
> +                return;

local_error needs to be propagated.

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