Re: [Qemu-devel] [PATCH v2] ui/vnc.c: polish vnc_init_func

[Markus Armbruster]

Fei Li <address@hidden> writes:

> Add a new Error parameter for vnc_display_init() to handle errors
> in its caller: vnc_init_func(), just like vnc_display_open() does.
> And let its callees propagate the Error, like init_keyboard_layout().
>
> Signed-off-by: Fei Li <address@hidden>
> ---
>  include/ui/console.h |  2 +-
>  ui/curses.c          |  4 +++-
>  ui/keymaps.c         | 11 ++++++-----
>  ui/keymaps.h         |  2 +-
>  ui/sdl.c             |  4 +++-
>  ui/vnc.c             | 16 +++++++++++-----
>  6 files changed, 25 insertions(+), 14 deletions(-)
>
> diff --git a/include/ui/console.h b/include/ui/console.h
> index fb969caf70..c17803c530 100644
> --- a/include/ui/console.h
> +++ b/include/ui/console.h
> @@ -453,7 +453,7 @@ void qemu_display_early_init(DisplayOptions *opts);
>  void qemu_display_init(DisplayState *ds, DisplayOptions *opts);
>  
>  /* vnc.c */
> -void vnc_display_init(const char *id);
> +void vnc_display_init(const char *id, Error **errp);
>  void vnc_display_open(const char *id, Error **errp);
>  void vnc_display_add_client(const char *id, int csock, bool skipauth);
>  int vnc_display_password(const char *id, const char *password);
> diff --git a/ui/curses.c b/ui/curses.c
> index 59d819fd4d..60c0962334 100644
> --- a/ui/curses.c
> +++ b/ui/curses.c
> @@ -28,6 +28,7 @@
>  #include <termios.h>
>  #endif
>  
> +#include "qapi/error.h"
>  #include "qemu-common.h"
>  #include "ui/console.h"
>  #include "ui/input.h"
> @@ -421,7 +422,8 @@ static void curses_keyboard_setup(void)
>          keyboard_layout = "en-us";
>  #endif
>      if(keyboard_layout) {
> -        kbd_layout = init_keyboard_layout(name2keysym, keyboard_layout);
> +        kbd_layout = init_keyboard_layout(name2keysym, keyboard_layout,
> +                                          &error_fatal);
>          if (!kbd_layout)
>              exit(1);

As Philippe pointed out, this exit() is now unreachable.

>      }
> diff --git a/ui/keymaps.c b/ui/keymaps.c
> index 43fe604724..52d432e856 100644
> --- a/ui/keymaps.c
> +++ b/ui/keymaps.c
> @@ -27,6 +27,7 @@
>  #include "sysemu/sysemu.h"
>  #include "trace.h"
>  #include "qemu/error-report.h"
> +#include "qapi/error.h"
>  
>  struct keysym2code {
>      uint32_t count;
> @@ -81,7 +82,7 @@ static void add_keysym(char *line, int keysym, int keycode, 
> kbd_layout_t *k)
>  
>  static kbd_layout_t *parse_keyboard_layout(const name2keysym_t *table,
>                                             const char *language,
`> -                                           kbd_layout_t *k)
> +                                           kbd_layout_t *k, Error **errp)
>  {
>      FILE *f;
>      char * filename;
> @@ -94,7 +95,7 @@ static kbd_layout_t *parse_keyboard_layout(const 
> name2keysym_t *table,
>      f = filename ? fopen(filename, "r") : NULL;
>      g_free(filename);
>      if (!f) {
> -        fprintf(stderr, "Could not read keymap file: '%s'\n", language);
> +        error_setg(errp, "could not read keymap file: '%s'", language);
>          return NULL;
>      }
>  
> @@ -118,7 +119,7 @@ static kbd_layout_t *parse_keyboard_layout(const 
> name2keysym_t *table,
>              continue;
>          }
>          if (!strncmp(line, "include ", 8)) {
> -            parse_keyboard_layout(table, line + 8, k);
> +            parse_keyboard_layout(table, line + 8, k, errp);

Lacks error checking.

Before this patch, an error in an included file is reported to stderr,
but is otherwise ignored:

    $ cat kbd-layout
    include bad
    include worse
    $ qemu-system-x86_64 -nodefaults -S -monitor stdio -display vnc=:0 -k 
kbd-layout
    QEMU 3.0.50 monitor - type 'help' for more information
    (qemu) Could not read keymap file: 'bad'
    Could not read keymap file: 'worse'

Afterwards, the error gets stored in errp.  If a second include fails,
we attempt to store another one, which fails the error_setv()'s
assertion:

    $ qemu-system-x86_64 -nodefaults -S -display vnc=:0 -k kbd-layout
    qemu-system-x86_64: /work/armbru/qemu/util/error.c:57: error_setv: 
Assertion `*errp == NULL' failed.
    Aborted (core dumped)

If it's the only failed include, parse_keyboard_layout() sets an error
and returns succes, which is a no-no.  Callers using the return value to
determine success are prone to leak the error, or run into
error_setv()'s assertion.  Callers using the error are prone to leak the
returned kbd_layout_t.

Let's address this in a separate patch before this one.

               if (!parse_keyboard_layout(table, line + 8, k, errp))

>          } else {
>              int offset = 0;
>              while (line[offset] != 0 &&
> @@ -170,9 +171,9 @@ static kbd_layout_t *parse_keyboard_layout(const 
> name2keysym_t *table,
>  
>  
>  kbd_layout_t *init_keyboard_layout(const name2keysym_t *table,
> -                                   const char *language)
> +                                   const char *language, Error **errp)
>  {
> -    return parse_keyboard_layout(table, language, NULL);
> +    return parse_keyboard_layout(table, language, NULL, errp);
>  }
>  
>  
> diff --git a/ui/keymaps.h b/ui/keymaps.h
> index 0693588225..98213a4191 100644
> --- a/ui/keymaps.h
> +++ b/ui/keymaps.h
> @@ -53,7 +53,7 @@ typedef struct {
>  typedef struct kbd_layout_t kbd_layout_t;
>  
>  kbd_layout_t *init_keyboard_layout(const name2keysym_t *table,
> -                                   const char *language);
> +                                   const char *language, Error **errp);
>  int keysym2scancode(kbd_layout_t *k, int keysym,
>                      bool shift, bool altgr, bool ctrl);
>  int keycode_is_keypad(kbd_layout_t *k, int keycode);
> diff --git a/ui/sdl.c b/ui/sdl.c
> index a5fd503c25..b33df70f4d 100644
> --- a/ui/sdl.c
> +++ b/ui/sdl.c
> @@ -29,6 +29,7 @@
>  #include <SDL.h>
>  #include <SDL_syswm.h>
>  
> +#include "qapi/error.h"
>  #include "qemu-common.h"
>  #include "qemu/cutils.h"
>  #include "ui/console.h"
> @@ -917,7 +918,8 @@ static void sdl1_display_init(DisplayState *ds, 
> DisplayOptions *o)
>          keyboard_layout = "en-us";
>  #endif
>      if(keyboard_layout) {
> -        kbd_layout = init_keyboard_layout(name2keysym, keyboard_layout);
> +        kbd_layout = init_keyboard_layout(name2keysym, keyboard_layout,
> +                                          &error_fatal);
>          if (!kbd_layout)
>              exit(1);

Again, exit() is now unreachable.

>      }
> diff --git a/ui/vnc.c b/ui/vnc.c
> index cf221c83cc..03c70b16f6 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -3205,7 +3205,7 @@ static const DisplayChangeListenerOps dcl_ops = {
>      .dpy_cursor_define    = vnc_dpy_cursor_define,
>  };
>  
> -void vnc_display_init(const char *id)
> +void vnc_display_init(const char *id, Error **errp)
>  {
>      VncDisplay *vd;
>  
> @@ -3222,13 +3222,14 @@ void vnc_display_init(const char *id)
>  
>      if (keyboard_layout) {
>          trace_vnc_key_map_init(keyboard_layout);
> -        vd->kbd_layout = init_keyboard_layout(name2keysym, keyboard_layout);
> +        vd->kbd_layout = init_keyboard_layout(name2keysym,
> +                                              keyboard_layout, errp);
>      } else {
> -        vd->kbd_layout = init_keyboard_layout(name2keysym, "en-us");
> +        vd->kbd_layout = init_keyboard_layout(name2keysym, "en-us", errp);
>      }
>  
>      if (!vd->kbd_layout) {
> -        exit(1);
> +        return;
>      }
>  
>      vd->share_policy = VNC_SHARE_POLICY_ALLOW_EXCLUSIVE;
> @@ -4079,7 +4080,12 @@ int vnc_init_func(void *opaque, QemuOpts *opts, Error 
> **errp)
>      char *id = (char *)qemu_opts_id(opts);
>  
>      assert(id);
> -    vnc_display_init(id);
> +    vnc_display_init(id, &local_err);
> +    if (local_err) {
> +        error_prepend(&local_err, "Failed to init VNC server: ");
> +        error_propagate(errp, local_err);
> +        return -1;
> +    }

Works, but is inconsistent with the handling of vnc_display_open()
errors, visible below.  Let's match that, and convert both to
error_propagate() in a followup patch.

>      vnc_display_open(id, &local_err);
>      if (local_err != NULL) {
>          error_reportf_err(local_err, "Failed to start VNC server: ");

I think the easiest way forward is for me to pick a touched up version
of this patch into a v2 of my "Replace some unwise uses of
error_report() & friends" series.  You'll receive a copy, of course.

Thanks!