qemu-char: Print strerror message on failure

The only way for chardev drivers to communicate an error was to return a NULL
pointer, which resulted in an error message that said _that_ something went
wrong, but not _why_.

This patch changes the interface to return 0/-errno and updates
qemu_chr_open_opts to use strerror to display a more helpful error message.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

console.c

@@ -1514,7 +1514,7 @@ static void text_console_do_init(CharDriverState *chr, DisplayState *ds)
         chr->init(chr);
 }
 
-CharDriverState *text_console_init(QemuOpts *opts)
+int text_console_init(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
     TextConsole *s;
@@ -1546,7 +1546,7 @@ CharDriverState *text_console_init(QemuOpts *opts)
 
     if (!s) {
         free(chr);
-        return NULL;
+        return -EBUSY;
     }
 
     s->chr = chr;
@@ -1554,7 +1554,9 @@ CharDriverState *text_console_init(QemuOpts *opts)
     s->g_height = height;
     chr->opaque = s;
     chr->chr_set_echo = text_console_set_echo;
-    return chr;
+
+    *_chr = chr;
+    return 0;
 }
 
 void text_consoles_set_display(DisplayState *ds)

console.h

@@ -354,7 +354,7 @@ void vga_hw_text_update(console_ch_t *chardata);
 
 int is_graphic_console(void);
 int is_fixedsize_console(void);
-CharDriverState *text_console_init(QemuOpts *opts);
+int text_console_init(QemuOpts *opts, CharDriverState **_chr);
 void text_consoles_set_display(DisplayState *ds);
 void console_select(unsigned int index);
 void console_color_init(DisplayState *ds);

hw/baum.c

@@ -576,7 +576,7 @@ static void baum_close(struct CharDriverState *chr)
     qemu_free(baum);
 }
 
-CharDriverState *chr_baum_init(QemuOpts *opts)
+int chr_baum_init(QemuOpts *opts, CharDriverState **_chr)
 {
     BaumDriverState *baum;
     CharDriverState *chr;
@@ -629,7 +629,8 @@ CharDriverState *chr_baum_init(QemuOpts *opts)
 
     qemu_chr_generic_open(chr);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 
 fail:
     qemu_free_timer(baum->cellCount_timer);
@@ -638,5 +639,5 @@ fail_handle:
     qemu_free(handle);
     qemu_free(chr);
     qemu_free(baum);
-    return NULL;
+    return -EIO;
 }

hw/msmouse.c

@@ -64,7 +64,7 @@ static void msmouse_chr_close (struct CharDriverState *chr)
     qemu_free (chr);
 }
 
-CharDriverState *qemu_chr_open_msmouse(QemuOpts *opts)
+int qemu_chr_open_msmouse(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
 
@@ -74,5 +74,6 @@ CharDriverState *qemu_chr_open_msmouse(QemuOpts *opts)
 
     qemu_add_mouse_event_handler(msmouse_event, chr, 0, "QEMU Microsoft Mouse");
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }

hw/msmouse.h

 /* msmouse.c */
-CharDriverState *qemu_chr_open_msmouse(QemuOpts *opts);
+int qemu_chr_open_msmouse(QemuOpts *opts, CharDriverState **_chr);

qemu-char.c

@@ -219,13 +219,15 @@ static int null_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
     return len;
 }
 
-static CharDriverState *qemu_chr_open_null(QemuOpts *opts)
+static int qemu_chr_open_null(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
 
     chr = qemu_mallocz(sizeof(CharDriverState));
     chr->chr_write = null_chr_write;
-    return chr;
+
+    *_chr= chr;
+    return 0;
 }
 
 /* MUX driver for serial I/O splitting */
@@ -634,18 +636,21 @@ static CharDriverState *qemu_chr_open_fd(int fd_in, int fd_out)
     return chr;
 }
 
-static CharDriverState *qemu_chr_open_file_out(QemuOpts *opts)
+static int qemu_chr_open_file_out(QemuOpts *opts, CharDriverState **_chr)
 {
     int fd_out;
 
     TFR(fd_out = qemu_open(qemu_opt_get(opts, "path"),
                       O_WRONLY | O_TRUNC | O_CREAT | O_BINARY, 0666));
-    if (fd_out < 0)
-        return NULL;
-    return qemu_chr_open_fd(-1, fd_out);
+    if (fd_out < 0) {
+        return -errno;
+    }
+
+    *_chr = qemu_chr_open_fd(-1, fd_out);
+    return 0;
 }
 
-static CharDriverState *qemu_chr_open_pipe(QemuOpts *opts)
+static int qemu_chr_open_pipe(QemuOpts *opts, CharDriverState **_chr)
 {
     int fd_in, fd_out;
     char filename_in[256], filename_out[256];
@@ -653,7 +658,7 @@ static CharDriverState *qemu_chr_open_pipe(QemuOpts *opts)
 
     if (filename == NULL) {
         fprintf(stderr, "chardev: pipe: no filename given\n");
-        return NULL;
+        return -EINVAL;
     }
 
     snprintf(filename_in, 256, "%s.in", filename);
@@ -665,11 +670,14 @@ static CharDriverState *qemu_chr_open_pipe(QemuOpts *opts)
 	    close(fd_in);
 	if (fd_out >= 0)
 	    close(fd_out);
-        TFR(fd_in = fd_out = open(filename, O_RDWR | O_BINARY));
-        if (fd_in < 0)
-            return NULL;
+        TFR(fd_in = fd_out = qemu_open(filename, O_RDWR | O_BINARY));
+        if (fd_in < 0) {
+            return -errno;
+        }
     }
-    return qemu_chr_open_fd(fd_in, fd_out);
+
+    *_chr = qemu_chr_open_fd(fd_in, fd_out);
+    return 0;
 }
 
 
@@ -760,12 +768,14 @@ static void qemu_chr_close_stdio(struct CharDriverState *chr)
     fd_chr_close(chr);
 }
 
-static CharDriverState *qemu_chr_open_stdio(QemuOpts *opts)
+static int qemu_chr_open_stdio(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
 
-    if (stdio_nb_clients >= STDIO_MAX_CLIENTS)
-        return NULL;
+    if (stdio_nb_clients >= STDIO_MAX_CLIENTS) {
+        return -EBUSY;
+    }
+
     if (stdio_nb_clients == 0) {
         old_fd0_flags = fcntl(0, F_GETFL);
         tcgetattr (0, &oldtty);
@@ -782,7 +792,8 @@ static CharDriverState *qemu_chr_open_stdio(QemuOpts *opts)
                                            display_type != DT_NOGRAPHIC);
     qemu_chr_set_echo(chr, false);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }
 
 #ifdef __sun__
@@ -969,7 +980,7 @@ static void pty_chr_close(struct CharDriverState *chr)
     qemu_chr_event(chr, CHR_EVENT_CLOSED);
 }
 
-static CharDriverState *qemu_chr_open_pty(QemuOpts *opts)
+static int qemu_chr_open_pty(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
     PtyCharDriver *s;
@@ -987,7 +998,7 @@ static CharDriverState *qemu_chr_open_pty(QemuOpts *opts)
     s = qemu_mallocz(sizeof(PtyCharDriver));
 
     if (openpty(&s->fd, &slave_fd, pty_name, NULL, NULL) < 0) {
-        return NULL;
+        return -errno;
     }
 
     /* Set raw attributes on the pty. */
@@ -1009,7 +1020,8 @@ static CharDriverState *qemu_chr_open_pty(QemuOpts *opts)
 
     s->timer = qemu_new_timer_ms(rt_clock, pty_chr_timer, chr);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }
 
 static void tty_serial_init(int fd, int speed,
@@ -1210,30 +1222,28 @@ static void qemu_chr_close_tty(CharDriverState *chr)
     }
 }
 
-static CharDriverState *qemu_chr_open_tty(QemuOpts *opts)
+static int qemu_chr_open_tty(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *filename = qemu_opt_get(opts, "path");
     CharDriverState *chr;
     int fd;
 
-    TFR(fd = open(filename, O_RDWR | O_NONBLOCK));
+    TFR(fd = qemu_open(filename, O_RDWR | O_NONBLOCK));
     if (fd < 0) {
-        return NULL;
+        return -errno;
     }
     tty_serial_init(fd, 115200, 'N', 8, 1);
     chr = qemu_chr_open_fd(fd, fd);
-    if (!chr) {
-        close(fd);
-        return NULL;
-    }
     chr->chr_ioctl = tty_serial_ioctl;
     chr->chr_close = qemu_chr_close_tty;
-    return chr;
+
+    *_chr = chr;
+    return 0;
 }
 #else  /* ! __linux__ && ! __sun__ */
-static CharDriverState *qemu_chr_open_pty(QemuOpts *opts)
+static int qemu_chr_open_pty(QemuOpts *opts, CharDriverState **_chr)
 {
-    return NULL;
+    return -ENOTSUP;
 }
 #endif /* __linux__ || __sun__ */
 
@@ -1347,7 +1357,7 @@ static void pp_close(CharDriverState *chr)
     qemu_chr_event(chr, CHR_EVENT_CLOSED);
 }
 
-static CharDriverState *qemu_chr_open_pp(QemuOpts *opts)
+static int qemu_chr_open_pp(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *filename = qemu_opt_get(opts, "path");
     CharDriverState *chr;
@@ -1355,12 +1365,13 @@ static CharDriverState *qemu_chr_open_pp(QemuOpts *opts)
     int fd;
 
     TFR(fd = open(filename, O_RDWR));
-    if (fd < 0)
-        return NULL;
+    if (fd < 0) {
+        return -errno;
+    }
 
     if (ioctl(fd, PPCLAIM) < 0) {
         close(fd);
-        return NULL;
+        return -errno;
     }
 
     drv = qemu_mallocz(sizeof(ParallelCharDriver));
@@ -1375,7 +1386,8 @@ static CharDriverState *qemu_chr_open_pp(QemuOpts *opts)
 
     qemu_chr_generic_open(chr);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }
 #endif /* __linux__ */
 
@@ -1417,21 +1429,24 @@ static int pp_ioctl(CharDriverState *chr, int cmd, void *arg)
     return 0;
 }
 
-static CharDriverState *qemu_chr_open_pp(QemuOpts *opts)
+static int qemu_chr_open_pp(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *filename = qemu_opt_get(opts, "path");
     CharDriverState *chr;
     int fd;
 
-    fd = open(filename, O_RDWR);
-    if (fd < 0)
-        return NULL;
+    fd = qemu_open(filename, O_RDWR);
+    if (fd < 0) {
+        return -errno;
+    }
 
     chr = qemu_mallocz(sizeof(CharDriverState));
     chr->opaque = (void *)(intptr_t)fd;
     chr->chr_write = null_chr_write;
     chr->chr_ioctl = pp_ioctl;
-    return chr;
+
+    *_chr = chr;
+    return 0;
 }
 #endif
 
@@ -1637,7 +1652,7 @@ static int win_chr_poll(void *opaque)
     return 0;
 }
 
-static CharDriverState *qemu_chr_open_win(QemuOpts *opts)
+static int qemu_chr_open_win(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *filename = qemu_opt_get(opts, "path");
     CharDriverState *chr;
@@ -1652,10 +1667,12 @@ static CharDriverState *qemu_chr_open_win(QemuOpts *opts)
     if (win_chr_init(chr, filename) < 0) {
         free(s);
         free(chr);
-        return NULL;
+        return -EIO;
     }
     qemu_chr_generic_open(chr);
-    return chr;
+
+    *_chr = chr;
+    return 0;
 }
 
 static int win_chr_pipe_poll(void *opaque)
@@ -1737,7 +1754,7 @@ static int win_chr_pipe_init(CharDriverState *chr, const char *filename)
 }
 
 
-static CharDriverState *qemu_chr_open_win_pipe(QemuOpts *opts)
+static int qemu_chr_open_win_pipe(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *filename = qemu_opt_get(opts, "path");
     CharDriverState *chr;
@@ -1752,10 +1769,12 @@ static CharDriverState *qemu_chr_open_win_pipe(QemuOpts *opts)
     if (win_chr_pipe_init(chr, filename) < 0) {
         free(s);
         free(chr);
-        return NULL;
+        return -EIO;
     }
     qemu_chr_generic_open(chr);
-    return chr;
+
+    *_chr = chr;
+    return 0;
 }
 
 static CharDriverState *qemu_chr_open_win_file(HANDLE fd_out)
@@ -1772,22 +1791,23 @@ static CharDriverState *qemu_chr_open_win_file(HANDLE fd_out)
     return chr;
 }
 
-static CharDriverState *qemu_chr_open_win_con(QemuOpts *opts)
+static int qemu_chr_open_win_con(QemuOpts *opts, CharDriverState **_chr)
 {
-    return qemu_chr_open_win_file(GetStdHandle(STD_OUTPUT_HANDLE));
+    return qemu_chr_open_win_file(GetStdHandle(STD_OUTPUT_HANDLE), chr);
 }
 
-static CharDriverState *qemu_chr_open_win_file_out(QemuOpts *opts)
+static int qemu_chr_open_win_file_out(QemuOpts *opts, CharDriverState **_chr)
 {
     const char *file_out = qemu_opt_get(opts, "path");
     HANDLE fd_out;
 
     fd_out = CreateFile(file_out, GENERIC_WRITE, FILE_SHARE_READ, NULL,
                         OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
-    if (fd_out == INVALID_HANDLE_VALUE)
-        return NULL;
+    if (fd_out == INVALID_HANDLE_VALUE) {
+        return -EIO;
+    }
 
-    return qemu_chr_open_win_file(fd_out);
+    return qemu_chr_open_win_file(fd_out, _chr);
 }
 #endif /* !_WIN32 */
 
@@ -1868,11 +1888,12 @@ static void udp_chr_close(CharDriverState *chr)
     qemu_chr_event(chr, CHR_EVENT_CLOSED);
 }
 
-static CharDriverState *qemu_chr_open_udp(QemuOpts *opts)
+static int qemu_chr_open_udp(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr = NULL;
     NetCharDriver *s = NULL;
     int fd = -1;
+    int ret;
 
     chr = qemu_mallocz(sizeof(CharDriverState));
     s = qemu_mallocz(sizeof(NetCharDriver));
@@ -1880,6 +1901,7 @@ static CharDriverState *qemu_chr_open_udp(QemuOpts *opts)
     fd = inet_dgram_opts(opts);
     if (fd < 0) {
         fprintf(stderr, "inet_dgram_opts failed\n");
+        ret = -errno;
         goto return_err;
     }
 
@@ -1890,16 +1912,17 @@ static CharDriverState *qemu_chr_open_udp(QemuOpts *opts)
     chr->chr_write = udp_chr_write;
     chr->chr_update_read_handler = udp_chr_update_read_handler;
     chr->chr_close = udp_chr_close;
-    return chr;
+
+    *_chr = chr;
+    return 0;
 
 return_err:
-    if (chr)
-        free(chr);
-    if (s)
-        free(s);
-    if (fd >= 0)
+    qemu_free(chr);
+    qemu_free(s);
+    if (fd >= 0) {
         closesocket(fd);
-    return NULL;
+    }
+    return ret;
 }
 
 /***********************************************************/
@@ -2178,7 +2201,7 @@ static void tcp_chr_close(CharDriverState *chr)
     qemu_chr_event(chr, CHR_EVENT_CLOSED);
 }
 
-static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
+static int qemu_chr_open_socket(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr = NULL;
     TCPCharDriver *s = NULL;
@@ -2188,6 +2211,7 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
     int do_nodelay;
     int is_unix;
     int is_telnet;
+    int ret;
 
     is_listen      = qemu_opt_get_bool(opts, "server", 0);
     is_waitconnect = qemu_opt_get_bool(opts, "wait", 1);
@@ -2213,8 +2237,10 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
             fd = inet_connect_opts(opts);
         }
     }
-    if (fd < 0)
+    if (fd < 0) {
+        ret = -errno;
         goto fail;
+    }
 
     if (!is_waitconnect)
         socket_set_nonblock(fd);
@@ -2266,14 +2292,16 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
         tcp_chr_accept(chr);
         socket_set_nonblock(s->listen_fd);
     }
-    return chr;
+
+    *_chr = chr;
+    return 0;
 
  fail:
     if (fd >= 0)
         closesocket(fd);
     qemu_free(s);
     qemu_free(chr);
-    return NULL;
+    return ret;
 }
 
 /***********************************************************/
@@ -2466,7 +2494,7 @@ fail:
 
 static const struct {
     const char *name;
-    CharDriverState *(*open)(QemuOpts *opts);
+    int (*open)(QemuOpts *opts, CharDriverState **chr);
 } backend_table[] = {
     { .name = "null",      .open = qemu_chr_open_null },
     { .name = "socket",    .open = qemu_chr_open_socket },
@@ -2506,6 +2534,7 @@ CharDriverState *qemu_chr_open_opts(QemuOpts *opts,
 {
     CharDriverState *chr;
     int i;
+    int ret;
 
     if (qemu_opts_id(opts) == NULL) {
         fprintf(stderr, "chardev: no id specified\n");
@@ -2527,10 +2556,10 @@ CharDriverState *qemu_chr_open_opts(QemuOpts *opts,
         return NULL;
     }
 
-    chr = backend_table[i].open(opts);
-    if (!chr) {
-        fprintf(stderr, "chardev: opening backend \"%s\" failed\n",
-                qemu_opt_get(opts, "backend"));
+    ret = backend_table[i].open(opts, &chr);
+    if (ret < 0) {
+        fprintf(stderr, "chardev: opening backend \"%s\" failed: %s\n",
+                qemu_opt_get(opts, "backend"), strerror(-ret));
         return NULL;
     }
 

spice-qemu-char.c

@@ -159,7 +159,7 @@ static void print_allowed_subtypes(void)
     fprintf(stderr, "\n");
 }
 
-CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
+int qemu_chr_open_spice(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
     SpiceCharDriver *s;
@@ -171,7 +171,7 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
     if (name == NULL) {
         fprintf(stderr, "spice-qemu-char: missing name parameter\n");
         print_allowed_subtypes();
-        return NULL;
+        return -EINVAL;
     }
     for(;*psubtype != NULL; ++psubtype) {
         if (strcmp(name, *psubtype) == 0) {
@@ -182,7 +182,7 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
     if (subtype == NULL) {
         fprintf(stderr, "spice-qemu-char: unsupported name\n");
         print_allowed_subtypes();
-        return NULL;
+        return -EINVAL;
     }
 
     chr = qemu_mallocz(sizeof(CharDriverState));
@@ -199,5 +199,6 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
 
     qemu_chr_generic_open(chr);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }

ui/qemu-spice.h

@@ -42,7 +42,7 @@ int qemu_spice_migrate_info(const char *hostname, int port, int tls_port,
 void do_info_spice_print(Monitor *mon, const QObject *data);
 void do_info_spice(Monitor *mon, QObject **ret_data);
 
-CharDriverState *qemu_chr_open_spice(QemuOpts *opts);
+int qemu_chr_open_spice(QemuOpts *opts, CharDriverState **_chr);
 
 #else  /* CONFIG_SPICE */