module: implement module loading

This patch adds loading, stamp checking and initialization of modules.

The init function of dynamic module is no longer directly called as
__attribute__((constructor)) in static linked version, it is called
only after passed the checking of presense of stamp symbol:

    qemu_stamp_$RELEASEHASH

where $RELEASEHASH is generated by hashing version strings and content
of configure script.

With this, modules built from a different tree/version/configure will
not be loaded.

The module loading code requires gmodule-2.0.

Modules are searched under
 - CONFIG_MODDIR
 - executable folder (to allow running qemu-{img,io} in the build
   directory)
 - ../ of executable folder (to allow running system emulator in the
   build directory)

Modules are linked under their subdir respectively, then copied to top
level of build directory for above convinience, e.g.:
    $(BUILD_DIR)/block/curl.so -> $(BUILD_DIR)/block-curl.so

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -201,6 +201,9 @@ Makefile: $(version-obj-y) $(version-lobj-y)
 libqemustub.a: $(stub-obj-y)
 libqemuutil.a: $(util-obj-y) qapi-types.o qapi-visit.o
 
+block-modules = $(foreach o,$(block-obj-m),"$(basename $(subst /,-,$o))",) NULL
+util/module.o-cflags = -D'CONFIG_BLOCK_MODULES=$(block-modules)'
+
 ######################################################################
 
 qemu-img.o: qemu-img-cmds.h

configure

@@ -1137,7 +1137,7 @@ Advanced options (experts only):
   --libdir=PATH            install libraries in PATH
   --sysconfdir=PATH        install config in PATH$confsuffix
   --localstatedir=PATH     install local state in PATH (set at runtime on win32)
-  --with-confsuffix=SUFFIX suffix for QEMU data inside datadir and sysconfdir [$confsuffix]
+  --with-confsuffix=SUFFIX suffix for QEMU data inside datadir/libdir/sysconfdir [$confsuffix]
   --enable-modules         enable modules support
   --enable-debug-tcg       enable TCG debugging
   --disable-debug-tcg      disable TCG debugging (default)
@@ -2362,14 +2362,32 @@ if test "$mingw32" = yes; then
 else
     glib_req_ver=2.12
 fi
-if $pkg_config --atleast-version=$glib_req_ver gthread-2.0; then
-    glib_cflags=`$pkg_config --cflags gthread-2.0`
-    glib_libs=`$pkg_config --libs gthread-2.0`
-    CFLAGS="$glib_cflags $CFLAGS"
-    LIBS="$glib_libs $LIBS"
-    libs_qga="$glib_libs $libs_qga"
-else
-    error_exit "glib-$glib_req_ver required to compile QEMU"
+
+for i in gthread-2.0 gmodule-2.0; do
+    if $pkg_config --atleast-version=$glib_req_ver $i; then
+        glib_cflags=`$pkg_config --cflags $i`
+        glib_libs=`$pkg_config --libs $i`
+        CFLAGS="$glib_cflags $CFLAGS"
+        LIBS="$glib_libs $LIBS"
+        libs_qga="$glib_libs $libs_qga"
+    else
+        error_exit "glib-$glib_req_ver $i is required to compile QEMU"
+    fi
+done
+
+##########################################
+# SHA command probe for modules
+if test "$modules" = yes; then
+    shacmd_probe="sha1sum sha1 shasum"
+    for c in $shacmd_probe; do
+        if which $c &>/dev/null; then
+            shacmd="$c"
+            break
+        fi
+    done
+    if test "$shacmd" = ""; then
+        error_exit "one of the checksum commands is required to enable modules: $shacmd_probe"
+    fi
 fi
 
 ##########################################
@@ -3661,6 +3679,7 @@ if test "$mingw32" = "yes" ; then
 fi
 
 qemu_confdir=$sysconfdir$confsuffix
+qemu_moddir=$libdir$confsuffix
 qemu_datadir=$datadir$confsuffix
 qemu_localedir="$datadir/locale"
 
@@ -3751,6 +3770,7 @@ echo "Install prefix    $prefix"
 echo "BIOS directory    `eval echo $qemu_datadir`"
 echo "binary directory  `eval echo $bindir`"
 echo "library directory `eval echo $libdir`"
+echo "module directory  `eval echo $qemu_moddir`"
 echo "libexec directory `eval echo $libexecdir`"
 echo "include directory `eval echo $includedir`"
 echo "config directory  `eval echo $sysconfdir`"
@@ -3890,6 +3910,7 @@ echo "sysconfdir=$sysconfdir" >> $config_host_mak
 echo "qemu_confdir=$qemu_confdir" >> $config_host_mak
 echo "qemu_datadir=$qemu_datadir" >> $config_host_mak
 echo "qemu_docdir=$qemu_docdir" >> $config_host_mak
+echo "qemu_moddir=$qemu_moddir" >> $config_host_mak
 if test "$mingw32" = "no" ; then
   echo "qemu_localstatedir=$local_statedir" >> $config_host_mak
 fi
@@ -4023,6 +4044,9 @@ if [ "$docs" = "yes" ] ; then
   echo "BUILD_DOCS=yes" >> $config_host_mak
 fi
 if test "$modules" = "yes"; then
+  # $shacmd can generate a hash started with digit, which the compiler doesn't
+  # like as an symbol. So prefix it with an underscore
+  echo "CONFIG_STAMP=_`(echo $qemu_version; echo $pkgversion; cat $0) | $shacmd - | cut -f1 -d\ `" >> $config_host_mak
   echo "CONFIG_MODULES=y" >> $config_host_mak
 fi
 if test "$sdl" = "yes" ; then

include/qemu/module.h

@@ -14,11 +14,31 @@
 #ifndef QEMU_MODULE_H
 #define QEMU_MODULE_H
 
+#include "qemu/osdep.h"
+
+#define DSO_STAMP_FUN         glue(qemu_stamp, CONFIG_STAMP)
+#define DSO_STAMP_FUN_STR     stringify(DSO_STAMP_FUN)
+
+#ifdef BUILD_DSO
+void DSO_STAMP_FUN(void);
+/* This is a dummy symbol to identify a loaded DSO as a QEMU module, so we can
+ * distinguish "version mismatch" from "not a QEMU module", when the stamp
+ * check fails during module loading */
+void qemu_module_dummy(void);
+
+#define module_init(function, type)                                         \
+static void __attribute__((constructor)) do_qemu_init_ ## function(void)    \
+{                                                                           \
+    register_dso_module_init(function, type);                               \
+}
+#else
 /* This should not be used directly.  Use block_init etc. instead.  */
 #define module_init(function, type)                                         \
-static void __attribute__((constructor)) do_qemu_init_ ## function(void) {  \
+static void __attribute__((constructor)) do_qemu_init_ ## function(void)    \
+{                                                                           \
     register_module_init(function, type);                                   \
 }
+#endif
 
 typedef enum {
     MODULE_INIT_BLOCK,
@@ -34,6 +54,7 @@ typedef enum {
 #define type_init(function) module_init(function, MODULE_INIT_QOM)
 
 void register_module_init(void (*fn)(void), module_init_type type);
+void register_dso_module_init(void (*fn)(void), module_init_type type);
 
 void module_call_init(module_init_type type);
 

module-common.c

+#include "config-host.h"
+#include "qemu/module.h"
+
+void qemu_module_dummy(void)
+{
+}
+
+void DSO_STAMP_FUN(void)
+{
+}

rules.mak

@@ -82,6 +82,8 @@ DSO_CFLAGS := -fPIC -DBUILD_DSO
 %$(DSOSUF): LDFLAGS += $(LDFLAGS_SHARED)
 %$(DSOSUF): %.mo libqemustub.a
 	$(call LINK,$^)
+	@# Copy to build root so modules can be loaded when program started without install
+	$(if $(findstring /,$@),$(call quiet-command,cp $@ $(subst /,-,$@), "  CP    $(subst /,-,$@)"))
 
 .PHONY: modules
 modules:
@@ -211,6 +213,7 @@ $(foreach o,$(filter %.o,$($1)),
 	$(eval $(patsubst %.o,%.mo,$o): $o) \
 	$(eval $(patsubst %.o,%.mo,$o)-objs := $o))
 $(foreach o,$(filter-out $(modules-m), $(patsubst %.o,%.mo,$($1))), \
+    $(eval $o-objs += module-common.o)
     $(eval $o: $($o-objs))
     $(eval modules-objs-m += $($o-objs))
     $(eval modules-m += $o)

scripts/create_config

@@ -108,6 +108,9 @@ case $line in
     value=${line#*=}
     echo "#define $name $value"
     ;;
+ DSOSUF=*)
+    echo "#define HOST_DSOSUF \"${line#*=}\""
+    ;;
 esac
 
 done # read

util/module.c

@@ -13,6 +13,8 @@
  * GNU GPL, version 2 or (at your option) any later version.
  */
 
+#include <stdlib.h>
+#include <gmodule.h>
 #include "qemu-common.h"
 #include "qemu/queue.h"
 #include "qemu/module.h"
@@ -21,13 +23,16 @@ typedef struct ModuleEntry
 {
     void (*init)(void);
     QTAILQ_ENTRY(ModuleEntry) node;
+    module_init_type type;
 } ModuleEntry;
 
 typedef QTAILQ_HEAD(, ModuleEntry) ModuleTypeList;
 
 static ModuleTypeList init_type_list[MODULE_INIT_MAX];
 
-static void init_types(void)
+static ModuleTypeList dso_init_list;
+
+static void init_lists(void)
 {
     static int inited;
     int i;
@@ -40,6 +45,8 @@ static void init_types(void)
         QTAILQ_INIT(&init_type_list[i]);
     }
 
+    QTAILQ_INIT(&dso_init_list);
+
     inited = 1;
 }
 
@@ -48,7 +55,7 @@ static ModuleTypeList *find_type(module_init_type type)
 {
     ModuleTypeList *l;
 
-    init_types();
+    init_lists();
 
     l = &init_type_list[type];
 
@@ -62,20 +69,154 @@ void register_module_init(void (*fn)(void), module_init_type type)
 
     e = g_malloc0(sizeof(*e));
     e->init = fn;
+    e->type = type;
 
     l = find_type(type);
 
     QTAILQ_INSERT_TAIL(l, e, node);
 }
 
+void register_dso_module_init(void (*fn)(void), module_init_type type)
+{
+    ModuleEntry *e;
+
+    init_lists();
+
+    e = g_malloc0(sizeof(*e));
+    e->init = fn;
+    e->type = type;
+
+    QTAILQ_INSERT_TAIL(&dso_init_list, e, node);
+}
+
+static void module_load(module_init_type type);
+
 void module_call_init(module_init_type type)
 {
     ModuleTypeList *l;
     ModuleEntry *e;
 
+    module_load(type);
     l = find_type(type);
 
     QTAILQ_FOREACH(e, l, node) {
         e->init();
     }
 }
+
+#ifdef CONFIG_MODULES
+static int module_load_file(const char *fname)
+{
+    GModule *g_module;
+    void (*sym)(void);
+    const char *dsosuf = HOST_DSOSUF;
+    int len = strlen(fname);
+    int suf_len = strlen(dsosuf);
+    ModuleEntry *e, *next;
+    int ret;
+
+    if (len <= suf_len || strcmp(&fname[len - suf_len], dsosuf)) {
+        /* wrong suffix */
+        ret = -EINVAL;
+        goto out;
+    }
+    if (access(fname, F_OK)) {
+        ret = -ENOENT;
+        goto out;
+    }
+
+    assert(QTAILQ_EMPTY(&dso_init_list));
+
+    g_module = g_module_open(fname, G_MODULE_BIND_LAZY | G_MODULE_BIND_LOCAL);
+    if (!g_module) {
+        fprintf(stderr, "Failed to open module: %s\n",
+                g_module_error());
+        ret = -EINVAL;
+        goto out;
+    }
+    if (!g_module_symbol(g_module, DSO_STAMP_FUN_STR, (gpointer *)&sym)) {
+        fprintf(stderr, "Failed to initialize module: %s\n",
+                fname);
+        /* Print some info if this is a QEMU module (but from different build),
+         * this will make debugging user problems easier. */
+        if (g_module_symbol(g_module, "qemu_module_dummy", (gpointer *)&sym)) {
+            fprintf(stderr,
+                    "Note: only modules from the same build can be loaded.\n");
+        }
+        g_module_close(g_module);
+        ret = -EINVAL;
+    } else {
+        QTAILQ_FOREACH(e, &dso_init_list, node) {
+            register_module_init(e->init, e->type);
+        }
+        ret = 0;
+    }
+
+    QTAILQ_FOREACH_SAFE(e, &dso_init_list, node, next) {
+        QTAILQ_REMOVE(&dso_init_list, e, node);
+        g_free(e);
+    }
+out:
+    return ret;
+}
+#endif
+
+void module_load(module_init_type type)
+{
+#ifdef CONFIG_MODULES
+    char *fname = NULL;
+    const char **mp;
+    static const char *block_modules[] = {
+        CONFIG_BLOCK_MODULES
+    };
+    char *exec_dir;
+    char *dirs[3];
+    int i = 0;
+    int ret;
+
+    if (!g_module_supported()) {
+        fprintf(stderr, "Module is not supported by system.\n");
+        return;
+    }
+
+    switch (type) {
+    case MODULE_INIT_BLOCK:
+        mp = block_modules;
+        break;
+    default:
+        /* no other types have dynamic modules for now*/
+        return;
+    }
+
+    exec_dir = qemu_get_exec_dir();
+    dirs[i++] = g_strdup_printf("%s", CONFIG_QEMU_MODDIR);
+    dirs[i++] = g_strdup_printf("%s/..", exec_dir ? : "");
+    dirs[i++] = g_strdup_printf("%s", exec_dir ? : "");
+    assert(i == ARRAY_SIZE(dirs));
+    g_free(exec_dir);
+    exec_dir = NULL;
+
+    for ( ; *mp; mp++) {
+        for (i = 0; i < ARRAY_SIZE(dirs); i++) {
+            fname = g_strdup_printf("%s/%s%s", dirs[i], *mp, HOST_DSOSUF);
+            ret = module_load_file(fname);
+            /* Try loading until loaded a module file */
+            if (!ret) {
+                break;
+            }
+            g_free(fname);
+            fname = NULL;
+        }
+        if (ret == -ENOENT) {
+            fprintf(stderr, "Can't find module: %s\n", *mp);
+        }
+
+        g_free(fname);
+    }
+
+    for (i = 0; i < ARRAY_SIZE(dirs); i++) {
+        g_free(dirs[i]);
+    }
+
+#endif
+}