hw/smbios: support loading OEM strings values from a file

Some applications want to pass quite large values for the OEM strings
entries. Rather than having huge strings on the command line, it would
be better to load them from a file, as supported with -fw_cfg.

This introduces the "path" parameter allowing for:

  $ echo -n "thisthing" > mydata.txt
  $ qemu-system-x86_64 \
    -smbios type=11,value=something \
    -smbios type=11,path=mydata.txt \
    -smbios type=11,value=somemore \
    ...other args...

Now in the guest

$ dmidecode -t 11
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.

Handle 0x0E00, DMI type 11, 5 bytes
OEM Strings
	String 1: something
	String 2: thisthing
	String 3: somemore

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200923133804.2089190-2-berrange@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/smbios/smbios.c

@@ -110,7 +110,7 @@ static struct {
 
 static struct {
     size_t nvalues;
-    const char **values;
+    char **values;
 } type11;
 
 static struct {
@@ -314,6 +314,11 @@ static const QemuOptDesc qemu_smbios_type11_opts[] = {
         .type = QEMU_OPT_STRING,
         .help = "OEM string data",
     },
+    {
+        .name = "path",
+        .type = QEMU_OPT_STRING,
+        .help = "OEM string data from file",
+    },
 };
 
 static const QemuOptDesc qemu_smbios_type17_opts[] = {
@@ -641,6 +646,8 @@ static void smbios_build_type_11_table(void)
 
     for (i = 0; i < type11.nvalues; i++) {
         SMBIOS_TABLE_SET_STR_LIST(11, type11.values[i]);
+        g_free(type11.values[i]);
+        type11.values[i] = NULL;
     }
 
     SMBIOS_BUILD_TABLE_POST;
@@ -940,9 +947,8 @@ static void save_opt(const char **dest, QemuOpts *opts, const char *name)
 
 
 struct opt_list {
-    const char *name;
     size_t *ndest;
-    const char ***dest;
+    char ***dest;
 };
 
 static int save_opt_one(void *opaque,
@@ -951,23 +957,60 @@ static int save_opt_one(void *opaque,
 {
     struct opt_list *opt = opaque;
 
-    if (!g_str_equal(name, opt->name)) {
-        return 0;
+    if (g_str_equal(name, "path")) {
+        g_autoptr(GByteArray) data = g_byte_array_new();
+        g_autofree char *buf = g_new(char, 4096);
+        ssize_t ret;
+        int fd = qemu_open(value, O_RDONLY, errp);
+        if (fd < 0) {
+            return -1;
+        }
+
+        while (1) {
+            ret = read(fd, buf, 4096);
+            if (ret == 0) {
+                break;
+            }
+            if (ret < 0) {
+                error_setg(errp, "Unable to read from %s: %s",
+                           value, strerror(errno));
+                return -1;
+            }
+            if (memchr(buf, '\0', ret)) {
+                error_setg(errp, "NUL in OEM strings value in %s", value);
+                return -1;
+            }
+            g_byte_array_append(data, (guint8 *)buf, ret);
+        }
+
+        close(fd);
+
+        *opt->dest = g_renew(char *, *opt->dest, (*opt->ndest) + 1);
+        (*opt->dest)[*opt->ndest] = (char *)g_byte_array_free(data,  FALSE);
+        (*opt->ndest)++;
+        data = NULL;
+   } else if (g_str_equal(name, "value")) {
+        *opt->dest = g_renew(char *, *opt->dest, (*opt->ndest) + 1);
+        (*opt->dest)[*opt->ndest] = g_strdup(value);
+        (*opt->ndest)++;
+    } else if (!g_str_equal(name, "type")) {
+        error_setg(errp, "Unexpected option %s", name);
+        return -1;
     }
 
-    *opt->dest = g_renew(const char *, *opt->dest, (*opt->ndest) + 1);
-    (*opt->dest)[*opt->ndest] = value;
-    (*opt->ndest)++;
     return 0;
 }
 
-static void save_opt_list(size_t *ndest, const char ***dest,
-                          QemuOpts *opts, const char *name)
+static bool save_opt_list(size_t *ndest, char ***dest, QemuOpts *opts,
+                          Error **errp)
 {
     struct opt_list opt = {
-        name, ndest, dest,
+        ndest, dest,
     };
-    qemu_opt_foreach(opts, save_opt_one, &opt, NULL);
+    if (!qemu_opt_foreach(opts, save_opt_one, &opt, errp)) {
+        return false;
+    }
+    return true;
 }
 
 void smbios_entry_add(QemuOpts *opts, Error **errp)
@@ -1149,7 +1192,9 @@ void smbios_entry_add(QemuOpts *opts, Error **errp)
             if (!qemu_opts_validate(opts, qemu_smbios_type11_opts, errp)) {
                 return;
             }
-            save_opt_list(&type11.nvalues, &type11.values, opts, "value");
+            if (!save_opt_list(&type11.nvalues, &type11.values, opts, errp)) {
+                return;
+            }
             return;
         case 17:
             if (!qemu_opts_validate(opts, qemu_smbios_type17_opts, errp)) {