[Qemu-devel] [PATCH 2/2] blockdev: Add dynamic module loading for block drivers

[Colin Lord <clord@redhat.com>]

From: Marc Mari <address@hidden>

Extend the current module interface to allow for block drivers to be loaded
dynamically on request.

The only block drivers that can be converted into modules are the drivers
that don't perform any init operation except for registering themselves. This
is why libiscsi has been disabled as a module.

All the necessary module information is located in a new structure found in
include/qemu/module_block.h

Signed-off-by: Marc Marí <address@hidden>
Signed-off-by: Colin Lord <clord@redhat.com>
---
 Makefile              |  3 --
 block.c               | 86 +++++++++++++++++++++++++++++++++++++++++++++------
 include/qemu/module.h |  3 ++
 util/module.c         | 37 ++++++----------------
 4 files changed, 90 insertions(+), 39 deletions(-)

diff --git a/Makefile b/Makefile
index 8f8b6a2..461187c 100644
--- a/Makefile
+++ b/Makefile
@@ -247,9 +247,6 @@ Makefile: $(version-obj-y) $(version-lobj-y)
 libqemustub.a: $(stub-obj-y)
 libqemuutil.a: $(util-obj-y)
 
-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
diff --git a/block.c b/block.c
index f54bc25..7a91434 100644
--- a/block.c
+++ b/block.c
@@ -26,6 +26,7 @@
 #include "block/block_int.h"
 #include "block/blockjob.h"
 #include "qemu/error-report.h"
+#include "qemu/module_block.h"
 #include "qemu/module.h"
 #include "qapi/qmp/qerror.h"
 #include "qapi/qmp/qbool.h"
@@ -242,11 +243,29 @@ BlockDriverState *bdrv_new(void)
 BlockDriver *bdrv_find_format(const char *format_name)
 {
     BlockDriver *drv1;
+    size_t i;
+
     QLIST_FOREACH(drv1, &bdrv_drivers, list) {
         if (!strcmp(drv1->format_name, format_name)) {
             return drv1;
         }
     }
+
+    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
+        if (!strcmp(block_driver_modules[i].format_name, format_name)) {
+            block_module_load_one(block_driver_modules[i].library_name);
+            /* Copying code is not nice, but this way the current discovery is
+             * not modified. Calling recursively could fail if the library
+             * has been deleted.
+             */
+            QLIST_FOREACH(drv1, &bdrv_drivers, list) {
+                if (!strcmp(drv1->format_name, format_name)) {
+                    return drv1;
+                }
+            }
+        }
+    }
+
     return NULL;
 }
 
@@ -447,8 +466,15 @@ int get_tmp_filename(char *filename, int size)
 static BlockDriver *find_hdev_driver(const char *filename)
 {
     int score_max = 0, score;
+    size_t i;
     BlockDriver *drv = NULL, *d;
 
+    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
+        if (block_driver_modules[i].has_probe_device) {
+            block_module_load_one(block_driver_modules[i].library_name);
+        }
+    }
+
     QLIST_FOREACH(d, &bdrv_drivers, list) {
         if (d->bdrv_probe_device) {
             score = d->bdrv_probe_device(filename);
@@ -470,6 +496,7 @@ BlockDriver *bdrv_find_protocol(const char *filename,
     char protocol[128];
     int len;
     const char *p;
+    size_t i;
 
     /* TODO Drivers without bdrv_file_open must be specified explicitly */
 
@@ -496,6 +523,7 @@ BlockDriver *bdrv_find_protocol(const char *filename,
         len = sizeof(protocol) - 1;
     memcpy(protocol, filename, len);
     protocol[len] = '\0';
+
     QLIST_FOREACH(drv1, &bdrv_drivers, list) {
         if (drv1->protocol_name &&
             !strcmp(drv1->protocol_name, protocol)) {
@@ -503,6 +531,23 @@ BlockDriver *bdrv_find_protocol(const char *filename,
         }
     }
 
+    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
+        if (block_driver_modules[i].protocol_name &&
+            !strcmp(block_driver_modules[i].protocol_name, protocol)) {
+            block_module_load_one(block_driver_modules[i].library_name);
+            /* Copying code is not nice, but this way the current discovery is
+             * not modified. Calling recursively could fail if the library
+             * has been deleted.
+             */
+            QLIST_FOREACH(drv1, &bdrv_drivers, list) {
+                if (drv1->protocol_name &&
+                    !strcmp(drv1->protocol_name, protocol)) {
+                    return drv1;
+                }
+            }
+        }
+    }
+
     error_setg(errp, "Unknown protocol '%s'", protocol);
     return NULL;
 }
@@ -525,8 +570,15 @@ BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
                             const char *filename)
 {
     int score_max = 0, score;
+    size_t i;
     BlockDriver *drv = NULL, *d;
 
+    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
+        if (block_driver_modules[i].has_probe) {
+            block_module_load_one(block_driver_modules[i].library_name);
+        }
+    }
+
     QLIST_FOREACH(d, &bdrv_drivers, list) {
         if (d->bdrv_probe) {
             score = d->bdrv_probe(buf, buf_size, filename);
@@ -2738,26 +2790,42 @@ static int qsort_strcmp(const void *a, const void *b)
     return strcmp(a, b);
 }
 
+static const char **add_format(const char **formats, int *count,
+                               const char *format_name)
+{
+    int i;
+
+    for (i = 0; i < *count; i++) {
+        if (!strcmp(formats[i], format_name)) {
+            return formats;
+        }
+    }
+
+    *count += 1;
+    formats = g_renew(const char *, formats, *count);
+    formats[*count] = format_name;
+    return formats;
+}
+
 void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
                          void *opaque)
 {
     BlockDriver *drv;
     int count = 0;
     int i;
+    size_t n;
     const char **formats = NULL;
 
     QLIST_FOREACH(drv, &bdrv_drivers, list) {
         if (drv->format_name) {
-            bool found = false;
-            int i = count;
-            while (formats && i && !found) {
-                found = !strcmp(formats[--i], drv->format_name);
-            }
+            formats = add_format(formats, &count, drv->format_name);
+        }
+    }
 
-            if (!found) {
-                formats = g_renew(const char *, formats, count + 1);
-                formats[count++] = drv->format_name;
-            }
+    for (n = 0; n < ARRAY_SIZE(block_driver_modules); ++n) {
+        if (block_driver_modules[n].format_name) {
+            formats = add_format(formats, &count,
+                                 block_driver_modules[n].format_name);
         }
     }
 
diff --git a/include/qemu/module.h b/include/qemu/module.h
index 2370708..4729858 100644
--- a/include/qemu/module.h
+++ b/include/qemu/module.h
@@ -52,9 +52,12 @@ typedef enum {
 #define qapi_init(function) module_init(function, MODULE_INIT_QAPI)
 #define type_init(function) module_init(function, MODULE_INIT_QOM)
 
+#define block_module_load_one(lib) module_load_one("block-", lib);
+
 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);
+void module_load_one(const char *prefix, const char *lib_name);
 
 #endif
diff --git a/util/module.c b/util/module.c
index ce058ae..dbc6e52 100644
--- a/util/module.c
+++ b/util/module.c
@@ -91,14 +91,11 @@ void register_dso_module_init(void (*fn)(void), module_init_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) {
@@ -163,14 +160,10 @@ out:
 }
 #endif
 
-static void module_load(module_init_type type)
+void module_load_one(const char *prefix, const char *lib_name)
 {
 #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;
@@ -181,15 +174,6 @@ static void module_load(module_init_type type)
         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 ? : "");
@@ -198,16 +182,15 @@ static void module_load(module_init_type type)
     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);
-            g_free(fname);
-            fname = NULL;
-            /* Try loading until loaded a module file */
-            if (!ret) {
-                break;
-            }
+    for (i = 0; i < ARRAY_SIZE(dirs); i++) {
+        fname = g_strdup_printf("%s/%s%s%s",
+                dirs[i], prefix, lib_name, HOST_DSOSUF);
+        ret = module_load_file(fname);
+        g_free(fname);
+        fname = NULL;
+        /* Try loading until loaded a module file */
+        if (!ret) {
+            break;
         }
     }
 
-- 
2.5.5